WyoInnovation

Moved to wyolum.com

2011-04-19T19:10:00.002-04:00

Hey, thanks for reading the wyoinnovation blog! If you want to now what we are up to know, go to http://wyolum.com.

Hope to see you there!

Wise Clock 3 Arrives!!

2011-03-19T10:58:00.000-04:00

Can't wait to see what pithy quotes come out of my new clock!

http://timewitharduino.blogspot.com/2011/01/introducing-wise-clock-3.html

Look for assembly notes and pictures soon.

Open Source Hardware Logo V3

2011-02-15T19:23:00.000-05:00

OSHW Logo V2

2011-02-15T07:53:00.000-05:00

Simplified the circuit board. Font is Liberation Sans Bold. Designed in Inkscape on Ubuntu.

Open Source Hardware Logo

2011-02-14T21:58:00.000-05:00

This is a concept logo for Open Source Hardware. Let me know what you think.

ClockTHREE Matrix Complete!

2010-12-11T09:21:00.000-05:00

ClockTHREE is Kickstarter "Project of the Day!"

2010-11-22T21:58:00.002-05:00

Suck on that, cool ipod watch thingy!

Mini Word Clock Available Online!

2010-11-19T08:13:00.000-05:00

Remember Alden's tiny word clock? Well he and Riley have taken that project to the next level by offering 100 of these clocks online for $59! The production version looks great with a clear back panel. Besides its handsome appearance, this is the most affordable word clock available. Congrats to Alden and Riley!

Alden is a contributor author to Make Magazine and a founding member of HacDC.

Kickstarter projected launched!

2010-11-16T09:19:00.003-05:00

Alright all you silent readers, now I need your help.
Anool has fixed the design files and we are ready to do another board run. Want one? Sign up at Kickstarter.com. Don't want one,but want to see us succeed anyway? Then please tell a friend.

http://www.kickstarter.com/projects/252714519/clockthree

Thanks!
Justin

Don't miss this super cool ipod watch thingy either!

Square Pegs

2010-11-06T18:04:00.000-04:00

NNNnnoooooooooo!

How do you fit a square peg into a round hole?

The set of holes on the right has been drilled out to accommodate the square leads of the LED. Compare those to the set of holes on the left which are the original size.

Anool is drilling out one board (over 700 holes) and we are getting the rest drilled at the factory (thousands of holes). The only problem is that we loose the connect through the board and will need to solder on both sides. Hope Anool can get a board built up this week and test the rest of the circuitry!

Rev two anyone?

ClockZWEI

2010-11-05T17:48:00.002-04:00

I wanted to see how difficult it would be to add another language. German! Now for some cool graphical effects. Not too difficult, but we need a real German to tweak it for us, volunteers? Code available here.

And now something new from the Overkill Department ...

2010-10-31T18:41:00.004-04:00

This clock reads the NMEA message from the GPS and sends it over to the 7-segment serial display.

This is just a simple application to experiment with GPS and serial display. The stack-up consists of a GPS module, a GPS shield, a double-tall ExtenderShield, and 7-segment serial display. In the photo, the flash washed out the LEDs, but this display is really bright (with digital dimmer options, too). The setup worked better than I expected. The GPS even got a location fix from my basement. This was one of the few projects where everything worked pretty much the first time, and only took about an hour.

... I'm thinking this would probably not be a good project to ship over seas right about now.

ClockTWO Simulator

2010-10-28T21:19:00.006-04:00

The ClockTWO boards should be completed in Mumbai today. Then it will take another couple of weeks to get a few sent here. In the meantime I've started working on the code.

This Python simulation with py2exe executable (to use: unzip, double-click dist/ClockTWO.exe) implements the same data structure that ClockTWO uses, so I can see if I am getting all the bits manipulated as I expect.

Controls to set the time:
s -- forward one second
S -- backward one second
m -- forward one minute
M -- backward one minute

f -- forward five minutes

F -- backward five minutes

h -- forward one hour

H -- backward one hour

The I, M, and D buttons emulate the hardware buttons. I moves forward one minute, D move back one minute, and M changes the color.

Please download, test, and provide feedback.

First Road Test

2010-10-22T09:59:00.003-04:00

The pitch tracking worked well. It was obvious that some yaw and roll tracking will be necessary. The lights come on when the rider looks around. Also sensitivity could be improved.

To that effect, Nat Dyck (college roommate) and I built up a Lego swing for the SharkFin. The swing allows the SharkFin to rotate while keeping the accelerometer at the center of rotation. Thus, the pitch measurement from the Accel. should be uncorrupted by the motion.

The second picture is a long exposure to show the center of rotation. It is not spinning nearly as fast as it looks.

Gyro Calibration: Done.

2010-10-17T12:48:00.010-04:00

Ok, so it has taken me eight months, but I finally have the SharkFin gyro calibration figured out. This should have been a simple task, but several technical issues combined with summer fun held up this project.

Recall that the SharkFin is a wireless helmet mounted inertial brake light for bicyclist. MEMS (read tiny) instruments measure accelerations and rotations to determine if the brakes are being applied and light the rear facing LEDs. Since the Bar End Brake Light and Amy's Brake Light were mounted directly to the bike, tracking the forward direction (against which braking is measured) was fairly simple. But sensors mounted on the helmet make it much more difficult, since the rider is constantly looking around. We (Anool and I) added a gyro, which measures rotational rate, to help keep track of the forward direction as the rider moves his head. We had some issues with our first analog board, but were able to substitute the SparkFun Razor 9DOF sensor board for the troubled sensors.

The trouble is that the gyro measurements are affected by temperature (and other things) that are not being measured, which impacts the knowledge of the forward direction enough to either shine the brake lights when no brakes are applied or to not apply the brakes under hard braking: two bad situations.

On a bike, light braking is about 1/20 G (where 1G is the amount of acceleration on the surface of the Earth due to gravity). In order for the SharkFin to work, the calibration needs to be accurate down to about 1/100G or about 10 cm / sec^2. This is a sensitive measurement for a dynamic platform. This magnitude of error would be caused by only 1/2 degree error in the pitch estimate.

Luckily, the onboard accelerometer can be used as an external rate measurement reference. It is not very accurate for a single measurement, but can be very accurate if averaged over a long period of time. This averaging allows us to continually track and update the gyro parameters and, hopefully, to keep the pitch measurement within that 1/2 degree tolerance mentioned above.

And there are other forces that need to be reckoned to meet this requirement. Namely, the centrifugal and tangential forces experienced by the sensors as the head rotates. In an extreme scenario, such as at a Metallica concert, these forces can be as large as a full G. Even in normal cases, they are too large to be ignored. The calibrated gyro measurements can be used to estimate and remove these not-braking accelerations.

Initially, I was optimistic that I could find some existing code that could be adapted to this situation, but no dice.

Details
Initial Gyro Cal
Here, we estimate the gain and bias parameters of the gyro offline. In this case, we assume the gyro parameters are static and estimate them using the accelerometer measurements (which is already well calibrated). The model for the gyro is linear. That means that the conversion of the integer counts c from the analog to digital converter (ADC) into an actual pitch rate is given by

omega = a c + b,

where a and b are the unknown parameters we seek. You may be more familiar with the related model:
omega = (c - d) f,
which is the same when f = a and -df = b. But this form has issues with linear estimation because the df term is quatratic. The actual pitch angle is the integral of the pitch rate. Subscripts are used to denote the measurement number: c0 is the first count, pitch0 is the first pitch and so on.

For a small amount of time dt, where small means that omega is not changing significantly over this time period, we can approximate the change in pitch as

pitch1 - pitch0 = (ac0 + b) dt, or

pitch1 = pitch0 + (ac0 + b) dt.

Continuing on,
pitch2 = pitch1 + (ac1 + b) dt or,
pitch2 = pitch0 + (ac0 + b) dt + (ac1 + b) dt or,
pitch2 = pitch0 + a dt(c0 + c1) + b 2 dt.

You get the idea:
pitchk = pitch0 + a dt (sum(ci) + b dt k.

If N measurements are taken, we have a system of N equations but only three unknowns (a, b, and theta0), in other words a very over determined system of equations. (We treat theta0 as an unknown, since the actual first measurement is corrupted and we don't want these errors to impact our estimate of a and b.) A little linear algebra makes this situation more manageable.

Let:
Pitch be the column vector of all of the pitch measurements taken from the accelerometer,
A be the N x 3 matrix with columns cumsum(C * DT), cumsum(DT), ones,
and x be the 3-vector [a, b, theta0],
C is the vector of gyro ADC counts,
DT is the vector of time deltas (dt s) in practice these may not be all equal,
ones is the vector of all ones.
The product C * DT is taken element wise.
Here cumsum is the cumulative sum of a vector. An example makes this clear:
cumsum([1, 2, 3, 3, 5]) = [1, 3, 6, 9, 14].

With this notation we have the much improved
Pitch = Ax.

This is easily solved using least sqares

x = (A^t A)^(-1) A^t Pitch,

where ^t is the matrix transpose of the preceding matrix.

That is it! I collected about 30 seconds worth of data pivoting the unit back and forth in my hand and got a really nice fit. The upper plot shows the pitch measurement for both the accelerometer and the gyro. The lower plot shows the difference between the two measurements. The astute reader might take issue with the large differences up to 10 degrees. This is because the accelerometer also as errors and I can't actually pivot about the gyro as I rotate the unit back and forth with my hands. I will set up a better calibration setup if this turns out to be too bad.

UPDATE 2010-10-22. Nat Dyck, my roommate from college, made me a fancy lego structure to calibrate the gyro. The device allows the SharkFin to spin with the accelerometer at the center of rotation. See road testing.

Doomsday Gyro Cal
... in which the continual gyro calibration is discussed.
So the gyro parameters a, and b need to be updated on a regular basis. We do this by updating our prior estimate with new information about the gyro parameters. In this case, since we cannot control the rider's head motion, we must accept the measurements that are provided. The rider my look down a lot to check the chain which would provide a great gain measurement a. Or the rider could hold perfectly still and provide a great bias measurement. One thing we to not want to do is to mess up a perfectly good prior gain estimate with new data.

We only get insight into the gain measurement when the rider is moving his head. If the rider is holding still we get a crappy gain measurement. Either way we get a gain measurement. It could be a good one, a bad one, or anything in between.

We want to update the prior gain estimate with this new information. Suppose we did something dumb and just averaged our prior gain estimate with the update.
gain_new = (gain_prior + gain_est) / 2.
If gain_est is bad, we just messed up our prior estimate with junk. If gain_est is really really good, we are messing up our gain_est with gain_prior. We really want a weighted average that balances how good we believe gain_est and gain_prior are.
Weighting by the inverse covariance does exactly that.

In other words we need to weight the new estimates by our confidence we have in them for each parameter. A great general purpose weighting scheme is to weight each term in the weighted average by its inverse covariance. When in doubt, this is the goto weighting scheme, optimal in several respects.

Our initial estimate of x comes with a covariance of that estimate. Provided we know the covariance of the input data (of Pitch in this case). Since the Pitch vector comes from independent accelerometer measurements, take

cov[Pitch] = sigma^2 I,

I being the NxN identity matrix, and sigma the standard deviation of the individual pitch measurements. Then the covariance of our estimate is

cov(x) = sigma^2 (A^t A)^-1.

This covariance tells us exactly how much we can trust our estimate. If we held very still during the collection period, the gain variance will be very large. The variance comes down the more rate diversity there is over the collection period.

So if we have two estimates for x , x1 and x2, along with the associated covariances cov1 and cov2, we can combine them into a single improved esitmate optimally as

x_new = (cov1^-1 + cov2^-1)^1 (cov1^-1(x1) + cov2^-1(x2)).
So we can keep a running estimate in this way by updated our prior estimate with the new data.

The covariance of x_new is already computed:
cov(x_new) = (cov1^-1 + cov2^-1)^1.

On thing the covariance above does not account for is the amount x changes between estimates. To account for this change we add a covariance term to represent it. This is sometimes referred to as plant noise, so I use the symbol cov_plant for it.

In the algorithm that follows, a shortcut has been made for simplicity. Since the Omega measurements are derived from the difference of two pitch measurements, they are not independent. The covariance matrix for Omega is actually tri-diagonal. The increased accuracy however does not justify the increased computational complexity, especially for an algorithm that is intended to run on a micro-controller.

Algorithm Doomsday Cal.
Inputs:
x_init -- the initial estimate for x.
cov_init -- covariance of x_init
K -- number of measurement to take between each cal update
sigma -- standard deviation of raw pitch measurement from accelometer
cov_plant -- un-modeled covariance

Outputs:
x -- A running estimate of the gyro parameters a and b.

#initialize

last_theta, last_time = measure theta, time

x = x_init

cov = cov_init

while 1: # loop forever (or until doomsday)

Omega = []

Count = [] 

for k in [0..K-1]:

measure theta, c, time

Omega.append((theta - last_theta) / (time - last_time))

Count.append(c)

last_theta = theta

last_time = time

A = column(Count, ones(K))

x_new = (A^t A)^(-1) A^t Omega

cov_new = sigma^2 (A^t A)^-1

x = (cov^-1 + cov_new^-1)^-1 (cov^-1(x) + cov_new^-1(x_new))

cov = (cov^-1 + cov_new^-1)^-1 + cov_plant

The gyro gain parameter seems to be very stable. We neither want nor expect this measurement to change much if at all. So in practice, cov_plant and cov_init can be made to prevent large updates to a by making the upper left element of these matrices to be very small implying very accurate prior knowledge of a.

Radial and Tangential Accelerations
These sensors are really good. The idea here is to use the gyro measurements to predict the non-braking accelerations and subtract them from the accerometer measurements before the braking estimate is made. It is really exciting to see this Math in Action, literally. We pose a simple circular model for the head movements and take two derivatives to get the acceleration. Comparing the expected results with actual measurements shows both that the model is right and how accurate these sensors are.
The circular model for head movements is:

p = r[sin(pitch), cos(pitch)],

where r is the radius of rotation, and p is the sensor position in the [Forward, Up] frame or f-u frame for short (no slight intended). One of the difficulties is keeping track of the sensor x-y frame relative to the f-u frame. That is, I guess, the entire problem.

The velocity vector is the time derivitive of the position vector. Using the chain rule from Calculus I (since pitch is also a function of time with dpitch / dt = omega) the velocity from head motion alone is computed as.

v = r[cos(pitch), -sin(pitch)] omega.

Recall that chain rule states that f(u(x))' - f'(u(x)) u'(x). The product rule is

[f(x) g(x)]' = f(x) g'(x) + f'(x) g(x)

Using the chain rule once again with the product rule and letting omegadot be the time rate of change of omega, the acceleration measurement is

a = -p omega^2 + v omegadot / omega.
or
a = R + T

where the radial R and tangential T components of the rotation acceleration are given by

R = -p omega^2 and
T = v omegadot / omega
= r[cos(pitch), -sin(pitch)] omegadot
The SharkFin was mounted to a bicycle wheel (see title picture) to confirm no major errors were made in the circular model calculations. A rubber band prevented the wheel from spinning more than 90 degrees. Over the 30 second run, the wheel was spun vigorously back and forth through its range of motion. In the pitcure below, the actual x-y acceleration measurements are transformed into f-u coordinates and compared to these R + T.

The blue line shows the f-u accelerations in Gs predicted from the gyro measurements. The green line shows the accelerometer measurements rotated into the f-u frame. The acceleration due to gravity, [0, 1] in the f-u frame, has been subtracted out as well. This is not a bad fit considering that the two measurements are completely independent.

The next plot shows the accelerations measured in the forward direction. This is the direction we are most concerned with for braking measurements.

The top plot shows the predicted and measured forward accelerations, the middle plot shows the difference between the two (the raw braking measurement). The lower shows the smoothed braking measurement. Ideally, since the motion is strictly circular with no braking involved, we would hope to see zero braking. Because of the large radius and vigorous motion, the errors creep up to .1 Gs. This should be much smaller for an actual helmet mount during non-head-banging activities. The upward trend is due to the gyro measurement drifting away from the true pitch measurement. This is dealt with by using the accelerometer measurements as an absolute, if noisy, reference.

That's it on gyro calibration. If you made it this far, congratulations. I've spared you the details of all of the mistakes and dead ends I have traversed. I'll save the full braking algorithm for another post.

Its about time: ClockTWO!

2010-10-12T22:05:00.003-04:00

I know you've been asking yourself, why is there no large open-source-hardware RGB LED array available? Anool and I wondered the same thing. You may have seen our earlier clock, the Worduino, based on Doug Jackson's ever popular Word Clock. This time, we decided to design a general-purpose Arduino based RGB array. The hefty 12 x 9 inch board supports up to 160 individually addressable RGB LEDs and an additional 32 mono LEDs which will easily accommodate a word clock. Our improved faceplate allows you to program reminders to hydrate with your favorite beverage. Looks like its "beer thirty" again. But, if you put a map transparency in front of it, you got the makings of a sunclock. Or maybe you just need some colorful scrolling text.

Those familiar with Evil Mad Science Peggy2 board will recognize the array architecture right away. It was a huge relief to start with a functional design and our hats are off to the the Evil Scientists! In addition to the array we have added a real time clock, light sensor, buzzer, and I2C interfaces for chaining boards horizontally end-to-end. The small squares on the right are pin compatible breakout boards, dubbed rtcBOB, that are pin compatible with the Chronodot.

Anool did a beautiful job with the layout and routing, painstakingly adding the myriad traces by hand. We ordered 10 boards for our initial run and plan to populate two test boards: one in India and one in the States. If it works like we hope, we will be making it available. If you want to get your hands on one early or have other questions or comments, drop us a line. We'd love to hear from you.

This is an open source hardware project (whatever that means). We will make all of the design files available when we decide on a (commercial friendly) licence.

EMSL Larson Scanner Review

2010-10-03T17:00:00.004-04:00

UPDATE October 2010. Safety by Prada!

My 14-year-old daughter put together the Larson Scanner Kit offered by the Evil Mad Science Laboratories (EMSL). We have put together quite a few soldering kits around here and this one is, simply put, the best "learn-to-solder" kit I've ever come across. There are several reasons for this. First off, the instructions are great. Not only are they clear, they leave no uncertainty as to what you need to do at each step, but they are in the form of a comic book, the perfect medium for this kit. This keeps the project light and fun.

Next, the kit is exactly the right depth. The circuit is simple enough to understood by a novice. It's just a controller, 9 LEDs, 9 current limiting resistors to prevent the LEDs from burning out, and a button. It took her about an hour to complete the kit from start to finish.

Which brings me to my next point: it's pretty freaking cool. When she turned it on for the first time, the LEDs began their smooth back and forth scanning. It is smooth because of the dimmer logic in the pre-programmed controller. It was actually a much cooler effect than I had anticipated. The mode button controls the speed of the scan as well as the brightness.

Because the project is open source, if she decides to, she can crack open the code and modify the functionality. What about a school logo POV? EMSL has provided the breakout for in circuit programming, serial communication, and two ports for customization.

The last salient feature I'd like to mention is the cost. At $13 flat, you can't go wrong.

Maybe it's me, but do I detect a hint of Evil Madness?

Liquidware Sensors Review

2010-07-27T21:10:00.004-04:00

Liquidware, the same folks who brought us the Open Source Hardware Bank have come out with a new line of sensor breakout boards that are worth taking a look at, especially if you are into Arduinos. Several factors distinguish the Liquidware boards from the others that are available.

They are targeted for Arduino. You can, of course, use them with any suitable micro controller out there, but they make it really quick and easy to get the sensors up and running on Arduino. Each sensor has a cheat sheet divided into three sections: "Learn," that describes the basic principles of the sensor; "Connect," that tells you how to connect the sensor to an Arduino, and "Code," that shows a minimal example of how to read data off the sensor. With these cheats, I was able to get the 3-axis accel and the ambiant light sensor up and running within 5 minutes (and to think that I had been putting this off for a month for lack of time).

I think these guys are on the right track here with these sensors. One improvement I might suggest, is to go beyond the basics on the cheat sheet. I think this could be accomplished by shrinking the font a bit and adding a column named "More" or something like that. This column would explain the full funtionality of the device. On the accel for instance, it'd definitely be a plus up to have a table for the G1 and G2 pins that affect the sensitivity of the unit. If done correctly, the new sheet will not frighten beginners, but will be more useful to the pros.

I've used a similar breakout board for the accelerometer (MMA7260QT) from Pololu, which cost about five bucks less. If you go this route, you might need a little more time getting up to speed.

Bottom Line:
If you are a seasoned pro, of course you will not NEED these hints, but even so, they will probably end up saving you some time getting things going.

If your new to electronics, these sensors can increase your chances of success using sophisticated sensors.

The days of the week (or how to pretend like you are a savant)

2010-06-13T10:25:00.007-04:00

Being able to tell what day of the week a date like October 28, 2012, will fall on seems like an impressive feet of computation. It is actually quite simple if you can memorize a few numbers.

My younger daughter Elizabeth and I have made a system whose only mental calculation is the addition of three numbers, all of which are less than seven. The sum of the three numbers indicates the day of the week. Sunday = 0, Monday = 1, and so on up to Saturday = 6. To complete the "savant" effect, say things like "Oh, that one is kinda bumpy so it is a Wednesday," or "Friday, it's blue and cold, definitely a Friday." If you decide to give it a go, be sure to try out my days of the week quiz program in the previous post to test yourself.

All of this math, takes place in the group of integers modulo 7, which simply means that we only care about the remainder of the number after dividing by 7. In this group, 8 and 1 are "equivalent" since 1 / 7 = 0 remainder 1, and 8 / 7 = 1 remainder 1. They both have the same remainder of one, after dividing by 7 so they are "equivalent" for our purposes. This boils down to the fact the we care ONLY about the day of the week, not how many weeks have passed or will pass between now and then. So we throw out the quotient and keep the remainder. To indicate that the computations are specific to integers modulo 7, "mod 7" is appended to each line. Here are some example calculations in this arithmetic:

0 + 0 = 0 mod 7
1 + 1 = 2 mod 7
4 + 3 = 0 mod 7
6 + 6 = 5 mod 7.

Try a few on your own:
3 + 3 = ? mod 7
5 + 2 = ? mod 7

Sometimes it is convenient to represent 6 as -1 mod 7. Since they share the same remainder after dividing by 7. With this in mind 6 + 6 = -1 + -1 mod 7 = -2 mod 7. Likewise -2 = 5 mod 7 and so on.

Each day, month, and year gets assigned an integer modulo 7. For instance in the carefully chosen example above:

October = > 0

28 = > 0

2012 = > 0,

so October 28, 2012 falls on a Sunday (0 + 0 + 0 = 0 mod 7).

So the arithmetic is simple. The tricky part is memorizing the number assignments for the months and years. Let's make it simple by only considering dates in the current year (2010) and focus on the months and day assignments. The year 2010 gets assigned a 4 (we will talk about why later).

The day assignments are the easiest: just take the day number modulo 7. The 15th of the month gets a 1 for instance since 15 = 1 mod 7.

The month assignments, in row order are:

Jan:0 Feb:3 Mar:3
Apr:6 May:1 Jun:4
Jul:6 Aug:2 Sep:5
Oct:0 Nov:3 Dec:5

or leaving off the month names for compactness:
0 3 3
6 1 4
6 2 4
0 3 5

In this system, this block of 12 numbers must be memorized backwards and forwards, by rows and by columns, inside, outside and upside-down. Some months are easier for me to remember than others:
January is a 0 (it starts everything off)
March is a 3 (third month of the year)
May is a 1 (May Day falls on May 1)
October is a 0 (The big O in October looks like a zero).

The others just need to be memorized. It's not actually that bad, but if you think of a good mnemonic, let me know.

A brief note on how the month assignments are made. January gets assigned a 0 to start things off. This is somewhat an arbitrary choice, but if you change it, you will also have to change the year assignments. Since January has 31 days and 31 = 3 mod 7, the first of Feb is three days of the week offset from the first of January, thus February gets assigned a 3. February has 28 days (exactly 4 weeks) most years so March 1st will fall on the same day as February 1st most years. Thus, we assign a 3 to March. March has 31 days which makes April 3 days offset from March (which was already 3 days offset from January 1st) , so April gets assigned a 6 (3 + 3 = 6 mod 7). Carry this process forward to compute the assignments for the other months.

With this in hand, you can compute any day of the week for the year 2010:
Oct 14, 2010 = > 0 + 0 + 4 = 4 mod 7, a Thursday
Mar 10, 2010 = > 3 + 3 + 4 = 3 mod 7, a Wednesday
July 4, 2010 = > 6 + 4 + 4 = 0 mod 7, a Sunday
...

Now to tackle the year assignments. Be sure to get really fast for the current year before you go any further.

For reasons that might become clear later, the year assignment is the day of the week that March 4th falls on. March 4, 2010, happens to be a Thursday, so 2010 is a 4. Using a calendar we get the following assignments for some nearby years:

2007 = > 0
2008 = > 2
2009 = > 3
2010 = > 4
2011 = > 5
2012 = > 0
2013 = > 1
2014 = > 2

Observe that the years go up by one whenever the year is NOT a leap year. For a leap year the assignments are 2 larger than the previous year. This makes since since 365 = 1 mod 7 for a normal year, and 366 = 2 mod 7 for a leap year. Zero years are thus convenient milestones to anchor the assignments for neighboring years. Elizabeth and I have dubbed a zero assigned year, like 2007, as a zear.

Every 28 years a zear falls on a leap year like 2012. These special years get a special name in this system. When a zear is also a leap year, it is refferred to as a le-zear pronounced "le" as in French with great flourish and accent on the second syllable: le-Zear!

Leap years require additional caution (Elizabeth always gets me on this!). If the date of interest is is in January or February of a leap year, subtract 1 from the count. Example:
January 25, 2012 = > 0 + 4 + 0 = 4 mod 7 - 1 = 3 Mod 7, a Wednesday.

Additional hints:
Within 100 years of 2000, the year assignments repeat every 28 years so 1970 gets the same assignment as 1998. This pattern is broken by the following fact.
1900 is NOT a leap year. Every one hundred years we skip a leap year, unless the year is divisible by 400.

Days of the week.

2010-05-28T19:32:00.002-04:00

I while back I wrote a day-of-the-week quiz program. Now for the life of me I can't find it. I re-wrote it. Here it is. Get good at it and amaze your friends.

ADXL345 Arduino Driver II

2010-05-24T06:47:00.001-04:00

I found a much more complete driver for this accelerometer thanks to Kevin Stevenard. I updated the code and renamed a few things. The changes were, unfortunately, not backward compatible. I've reposted the modified code here.

Thanks Kevin!

Arduino: undefined reference to `loop'

2010-05-23T15:03:00.003-04:00

Ok, since this is the second time this has baffled me, I am making a note to myself. It turns out you cannot have a library with the same name as the pde file.

This is the example that got me. The Arduino project .pde file is a test of an accelerometer library (Adxl345.cpp, .h). Here is what the directory listing looks like.
.../sketchbook/Adxl345/Adxl345.pde
.../sketchbook/Adxl345/Adxl345.cpp
.../sketchbook/Adxl345/Adxl345.h

This yeilds the cryptic error
undefined reference to `loop'

or sometimes
undefined reference to `setup'

or both. The fix is to rename the Arduino project as anything other than "Adxl345". Using "Save As" in arduino should do the trick. This is what the listing looks like that works:

.../sketchbook/Adxl345_test/Adxl345_test.pde

.../sketchbook/Adxl345_test/Adxl345.cpp

.../sketchbook/Adxl345_test/Adxl345.h.

ADXL345 Arduino Driver

2010-05-14T13:28:00.001-04:00

I wrote a simple driver for the ADXL345 accelerometer on the Razor board. The code provides read/write access to the registers on the device and allows you to change the bandwidth of the internal low pass filter. This little chip has an in-depth interface with stream buffering, fall detection, bump detection, double click detection besides autonomous low pass filtering. I have only scratched the surface here.

A simple test script is located in the examples directory.

WORDUINO Instructions

2010-05-12T21:34:00.004-04:00

Anool has prepared a beautiful set of instructions for our WordClock. Unfortunately, there are only 6 copies of the boards so consider yourself lucky if you got a set. If anyone expresses an interest, we may make more of the next edition of WORDUINO. Please let us know if you are interested.

The flexible faceplate lettering has been laser etched.

This picture shows the laser cut baffles to isolate the light to individual words.

SharkFin Sensor Swap -- SFSS

2010-05-08T09:36:00.006-04:00

I take it back. On the original SharkFin, the analog circuitry was causing a small error in both the gyro and accel measurements. We've since corrected the design, but we didn't want to lay money down on a new set of boards until the concept was proven.

Along comes the 9 degree of freedom Razor IMU from SparkFun. This $125 bad boy has 3 axes of accel, 3 of gyro and 3 magnetometer, overkill for sure. I got this for experimentation and found out that it fit beautifully on Fin. The holes even lined up. This amazing foresight by Anool, enabled the sensor swap.

The 9 dof razor has a ATMEGA328 on board already. I reprogrammed the MEGA on the SharkFin base to be a digital slave dummy. It just listens on the serial port for 3 byte messages which it assigns to the digital ports: PORTB, PORTC, and PORTD. This simple interface could be expanded to also read digital inputs from the slave.

The accel datasheet indicates a selectable bandwidth. It is unclear on exactly how this is being accomplished, but if it is effective, this will relieve the huge burden on the processor of low-pass filtering the accel data.

The magnetometer offers the possibility of complete head orientation tracking. It is still unclear exactly how to take advantage of this given that there is no true velocity measurement. Ideas are welcome!

Anool receives Alden's minature WordClock.

2010-05-08T07:53:00.002-04:00

After over a month, Anool finally received the package containing Alden's miniature WordClock. Here are some photos of his careful vivisection.

WordClock Delivered

2010-05-01T19:09:00.002-04:00

I dropped off a word clock to Alden (creator of the miniature word clock). I had mistakenly come to the conclusion that Alden had a laser cutter. I will forward the super cool golden face plates when they arrive from Anool. You can see the word clock on the left of the work bench.

While I was there he showed me around his beautiful shop. This is a dream shop, well lit and spacious, with enough components on hand to invent the future (which is what he is doing!).

Below, Alden is checking the performance of a stepper driver he has been working on. The steppers must have gotten out of hand in the second photo as the whole room seems to be spinning.

Yet Another WordClock

2010-04-18T22:50:00.002-04:00

First pass I tried to save room by soldering the power cord directly into the board. It turned out there was plenty of space on the back side of the board as seen below.

The boards are held in place with surplus proto-board. A slit has been cut in the corner of the the enclosure from the outside of the box to accept the holder. This keeps the board stable in both forward and backward directions.

Still missing the baffels, but the result is easily readable.

Laser Cut Face and Baffels

2010-04-16T00:01:00.001-04:00

Unhappy with how the clock face turned out, Anool, redesigned them to be laser cut and the results speak for themselves!

He is testing a diffuser over "O'CLOCK", that is how the final product will look.

WordClock boards have arrived

2010-04-12T23:35:00.006-04:00

The WordClock board from Anool arrived!
The clock consists of three boards: Main board which houses the ICs, the LED board and the face (pictures to come)

Everything seems to be working except the reset from the FTDI interface. hmmm.

Yet another blinking light, and it is a miracle every time!

SharkFin-- The first wireless helmet mounted brake light!

2010-03-28T00:34:00.002-04:00

I've been consumed for the past month with the SharkFin. The gyro drift and analog glitches nearly did me in. I am reporting in the wee hours of the morning today, that the first version is functional! May still need to play with the thresholds after road testing but, (famous last words) I feel confident that there are no more major hurdles! More pics and vids to come.

Hurray!

HACDC Lightning Talk

2010-02-24T20:12:00.003-05:00

I made it through a few of the charts of my Lightning Talk before my 5 minutes was up at HAC DC last night. It was a great evening of amazing presentations and after all the presentations were done, Alden Hart gave me a beautiful and tiny word clock. I'll put the link to the video here when it's available.

IT WORKS!!!!

2010-02-20T01:02:00.001-05:00

The boards arrived FedEx this morning from Mumbai. I got right to work on the first prototype when I got home. It friggin worked the first try! The boards exceeded all of my expectations! Lights work. Sensors work. Serial port works. Unbelievable.
Three cheers for Anool! Three cheers for SharkFin!

Strap-On Shark Fin Boards!

2010-02-12T10:41:00.000-05:00

Anool has completed the machining of the Strap-On Shark Fin boards and they came out beautifully. Half of them will be arriving from India soon!

1^2 + 2^2 + 3^2 + 4^2 + 5^2 + ... + n^2

2010-02-11T09:36:00.013-05:00

It is well know that the sum of the squares of integers S is n(n+1)(2n+1)/6. And proofs abound. Although this relationship is not difficult to prove by mathematical induction, it is not intuitively satisfying. This visual proof is very clear and easy to understand.

Elizabeth, my 10-year-old daughter, wanted to figure out the volume of a sphere. Making approximations using 16 equal thickness coin shaped cylinders as seen below.

We ended up with an expression that contained in part, the sum 1 + 4 + 9 + 16 + 25 + 36 + 49 + 64. It was clear that if we had used instead n coins each of width 1/n, to approximate the volumn, part of that expression would intail the sum Sn = 1 + 4 + 9 + 25 + ... + n^2. To no avail, I looked around for a simple way to demonstrate the well known relationship:

Sn = n(n+1)(2n+1)/6.

Imagine the sum Sn as the volume of the pyramid of 1 x 1 x 1 cubes with one cube on the top layer, 4 on the next, 9 on the next and so on up to n x n cubes on the bottom layer as seen in the figure above.

From the expression Sn =n(n+1)(2n+1)/6, we see that Sn is one sixth the volume of a box with dimensions n x (n + 1) x (2n + 1). So it is at least conceivable that six of these pyramids could be packed into that rectangular volume. Elizabeth and I glued 30 wooden cubes into 6 two-layer pyramids (1 x 1 + 2 x 2) as shown

and without too much effort arranged them into a 2 x 3 x 5 rectangular volume.

The configuration is general, in that it can be scaled up to any positive integer n. Here are some screen shots of a Python simulation using n=4 demonstrating the configureation.

Now fast forward a few days. Snowmaggeddon has snowed me OUT of Reston, VA, and I'm stuck in LA on a rainy Saturday. Amy (lovely wife) scouts out a meeting of the LA Microcontrollers Club from the Make Blog. The once-a-month meeting was scheduled to start in only three hours. A quick peak at the map revealed Topanga, CA, to be just up the mountain North of Santa Montica, about a forty-five minute drive from my hotel. Sweet.

Luckily, I got an early start because the direct route was closed because of the Niagra of mudslides. Rerouting was tricky with my gps-phone rebooting every two minutes. I finally arrived at this beautiful location at the end of a mile-long jeep trail. The Ford Focus I was driving had trouble negotiating the rutted climb, but the view was worth it.

It was fun getting to know Jack, the founder of the LA Mircrocontroller Club and freelance maker (see see buffingtonfx.com) and Nick, a freelance Hollywood tech.

Nick brought his Arduino-based movie prop clock that stays on whatever time you set it and won't flicker when filmed. Jacked showed off his awesome shop, with a DIY CNC router, and shared his recent experience with the Propeller development board.

Getting to the point, Jack kindly offered to route out the pyramid shapes with his CNC router. Literally, an hour later, Jack had produced three perfect five-layer pyramids. He would have made all six, but I was already late for another appointment. Had I known that Jack was planning to give the pyramids to me, I definitely would have waited for the top half of the retangular volume!

Thanks Jack!

SharkBoot (Arbitrary clock speed)

2010-02-10T16:12:00.002-05:00

To save batteries, Anool are considering running the SharkFin at 3.3V with a 12 MHz resonator. That means that the bootloader needs to be recompiled with the new CPU speed.

Steps:
1. Download Makefile from ladyada.net here.
2. Add new target by modifying adaboot328 to Makefile (I called it sharkfin328)

sharkfin328: TARGET = sharkfin328
sharkfin328: CFLAGS += '-DMAX_TIME_COUNT=F_CPU>>2' '-DNUM_LED_FLASHES=3'  '-DWATCHDOG_MODS'
sharkfin328: $(PROGRAM)_sharkfin328.hex
sharkfin328: AVR_FREQ = 12000000L 
sharkfin328: MCU_TARGET = atmega328p
sharkfin328: LDSECTION  = --section-start=.text=0x7800

3. >make sharkfin328
4. Upload see here for details.

The new board will look like a "Arduino Duemilanove or Nano w/ ATmega328" inside of Arduino.

BEBL Board Has Arrived!

2010-01-30T18:43:00.006-05:00

The boards Anool sent before Christmas have finally arrived. Looks like the envelope got hung up in the sorter as you can see the torn corner. No worries, the boards arrived unharmed and they are even smaller than I had imaged, 2x5cm.

Now to find a case...

UPDATE

Emily found this tiny Altoids tin that is just right!

Bootloader woes!

2010-01-30T17:28:00.017-05:00

I have some AVR 328s that I'd like to upgrade to LadyAda's bootloader. Which has a couple of features for homemade arduino boards:

1. Three flashes on reset. Her bootloader flashes pin 13 when reset occurs.

2. Upload flicker on pin 13.

Although not absolutely necessary, it sure is nice to get the positive feedback that things are working when any number of things can go wrong with a home build duino.

The MegaISP seemed to work ok, but requires 2 arduinos to program a new Mega chip: one to run MegaISP, and one to house the chip to be programmed. I thought I could simplify things by buying this programmer, but it has been difficult to get this working.

Here is how I got it working on my Linux box.

1. Power the chip. The programmer does not supply the power to the chip as I discovered. So I was beating a dead horse for a day not knowing this simple fact.

2. Disconnect anything from the board. When I powered the board, I still got the same error. avrdude stk_500v2 not responding. I had an LED connected to pin 13 that I guess was sapping the signal from the micro back to the computer.

3. Plug programmer into usb port. You should see a device /dev/ttyACM0 or similar. That is the programmer. Green light on programmer should be on. If you are an avrdude guru, you probably already know to use the -P /dev/ttyACM0 option. I had trouble getting avrdude to write the efuse, so I tried using Arduino IDE to write the bootloader.

4. Unplug arduino from usb, power it with a 9v or otherwise through VIN. We are going to program the chip through /dev/ttyUSB0 and we don't want to figure out if USB0 is the programmer or the duino. Just unplug it from the usb all together and use external power.

5. Arduino IDE expects to see the programming sitting at /dev/ttyUSBX and it is actually at /dev/ttyACM0. The solution here is so simple I never thought it would work. Use a soft link. I don't remember where I found this solution, but it works.
> sudo ln -s /dev/ttyACM0 /dev/ttyUSB0

6. Select Tools->Burn Bootloader->w/AVRISP mkii. After a couple of minutes the bootloader is loaded.

7. Upload blink.pde. If this loaded congratulations. This worked for me with the standard bootloader: ATmegaBOOT_168_atmega328.hex.

8. Move standard bootloader for safekeeping, cd to Arduino/hardware/bootloaders/atmega/
> mv ... /bootloaders/atmega/ATmegaBOOT_168_atmega328.hex /bootloaders/atmega/ATmegaBOOT_168_atmega328.hex-orig

9. Copy AdaBoot to expected bootloader location
>mv ATmegaBOOT_xx8_adaboot328.hex /bootloaders/atmega/ATmegaBOOT_168_atmega328.hex

10. Tools->Burn Bootloader->w/AVRISP mkii (again)

11. Upload blink.pde. This is where I am stuck. Blink will not upload. I see this in the output window after I see the 3 blink reset (so I know adaboot is running):
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding

Manual reset (at different delays from upload click) makes no difference.

UPDATE!
LadyAda suggested that perhaps the baud rate for the hex file I was using was 19200. This turned out to be the case. I modified */hardware/boards.txt by changing

atmega328.upload.speed=57600

to
atmega328.upload.speed=19200

and got blink.pde to upload and run. Thanks LadyAda! The real fix is to upload the 57600 hex adaboot file. Look for an uplate when I get this to run.

UPDATE:

I recompiled LadyAda's AdaBoot with the baudrate changed to 57600. Download the hex file here.

Or, to compile it yourself:

Download and unzip AdaBoot.

Change the baudrate in the C source code will do the trick. Line 90 of the source code reads:

#define BAUD_RATE 19200

Change this to

#define BAUD_RATE 57600

Then from the command line:

> make adaboot328

If you have all everything you need installed you will generate a hex file. Or you can use this 57600 hex file if you don't.

To upload with avrdude only try just talking to the chip first:
> avrdude -c stk500v2 -p m328p -P /dev/ttyACM0
(change -P as necessary)

If that works, this script will upload the hex file using only avrdude
#!/bin/sh
# change -P as necessary
#
# find extended, high, low, lock, and unlock bits on hardware.txt
OPTS="-c stk500v2 -p m328p -P /dev/ttyACM0"
avrdude $OPTS -U efuse:w:0x05:m
avrdude $OPTS -U hfuse:w:0xda:m
avrdude $OPTS -U lfuse:w:0xff:m
avrdude $OPTS -U lock:w:0x3f:m
avrdude $OPTS -U flash:w:ATmegaBOOT_xx8_adaboot328.hex:i
avrdude $OPTS -U lock:w:0x0f:m

Here is a picture of the programming setup. I had to stack several 2 x 14 DIL sockets to make room for the 6 pin programming cable. The green socket has a lever that releases the chip... handy.

AdaBoot: Succeed!

6-22-2010 Update:
I am pleased to confirm that this process works with fresh ATMEGA 328 chips (no previous bootloader installed).

May 30, 2011 UPDATE:

I just got a new set of MEGAs from digikey with a different device signature.
The old signature that avrdude expected is
"0x1e950f".

The chips I received with the same part number had a signature of
"0x1e9514".

There are two ways to handle this. The easiest is to use the -F option with avrdude to force it into action regardless of the signature. The second is to change the device signature in avrdude.conf (mine was located in /etc/avrdude.conf). Search for 328, then search again for signature. I commented out the existing line and modified it like so
# signature = 0x1e950f
signature =0x1e9514

This works like a charm until you need to program older chips in which case you need to revert to the original version.

Good bye suburban ignorance...

2010-01-19T18:20:00.004-05:00

Hello Urban Awareness!

Jacket finally arrived today, we were all dazzled by the glow of the coat and by our new found urban/youthy chicness.

This coat rocks.

First Draft SharkFin Layout!

2010-01-18T18:14:00.002-05:00

Anool, turned around the sketch below into the layout seen here in 12 hours, and he has a real job to boot! I'm starting to think the SharkFin is going to become a reality. Priya has offered to help out with the enclosure, with her eye for design, we have a hit for sure.

SharkFin Preliminary Layout

2010-01-17T15:06:00.007-05:00

Here is a rough layout for the SharkFin.

Notes:
1. The lower right hand corner is square. All components are aligned relative to this corner. The actual orientation will put the LEDs horizontal.
2. SparkFun and Pololu make the layouts for the three daughter boards available. It may save a lot of space and money to put those parts right on the motherboard. For know, routing can be done underneath of the daughter boards.
3. S1 is reset, S2 is for mode changing (night/day), S3 is power, and SEL is power select.
4. Note Power Down pin on Gyro is grounded. This stops spontaneous shutting down of the gyro.
5. I'm not sure if power select is required. I'm worried that I would be able to communicate through the USB at the 3.3V level provided by the power supply circiut.
6. The ATMega 328 is only rated at 12MHz for 3.3V. Not sure how this will impact serial connection. Might just fudge a little and try the 16MHz osc at 3.3V. Seems to work on the BEBL!
7. Routing may be tricky. Looks like a two sided board to me.
8. D5 is not an LED, but a Zener Diode as for programming feedback ala LadyAda's supped up boot loader.
9. The two large circles are through holes for mounting the board to the helmet.

Anool's Brake Light: Succeed

2010-01-14T18:17:00.012-05:00

Anool has completed his brake light and it looks awesome! He started by prototyping on the Duemilanove. Once he understood the circuit, he designed a printed circuit board. Finally he designed and built this elegant project enclosure. The aluminium mount doubles as a power jumper, eliminating the need for a separate switch.

Great job Anool!

The central blue LED was too bright and had to be turned off to capture this video.

Brake Light Mod!

2010-01-12T17:55:00.004-05:00

Instructables reader, Anool, has printed up some PCB's from the BEBL schematic. This larger 5-light version will be mounted on the seatpost. He was generous enough to send me a couple of the boards. I'll be looking forward to receiving them.

If all goes well, Anool and I will have the SharkFin boards ready soon!

Thanks Anool!

Scopy

2009-12-30T15:29:00.004-05:00

To debug the gyro voltage on the SharkFin, I made a simple Arduino based oscilloscope. Single channel, no triggers, no frills.

Python, pylab, and gtk are required.

1. upload scope.pde to arduino

2. edit scopy.py to point to your Arduino (see Tools->Serial Port in Arduino IDE)

3. run scopy.py on computer

4. if you improve either, please send me the update.

BEBL Takes "Light Up the Night" Grand Prize!

2009-12-15T18:56:00.003-05:00

WOW, Instructables just announced that the BEBL won the Light Up the Night Contest! They are shipping out the sweet Grand Prize "Urban Awarness Jacket" from Cordarounds.

I entered the contest on a lark when I entered the Arduino Contest. Who would have guessed?

Thanks for all the support!

BEBL Instructable takes 2nd Prize

2009-12-03T20:11:00.002-05:00

The BEBL instructable took 2nd prize in the instructables Arduino contest. Thanks to everyone who voted!

BEBL Links

2009-11-06T14:58:00.006-05:00

BEBL Challenge
Source Code
Digital Filtering
Latest Schematic
Accel Power Supply Solution
Trouble Shooting
First Try
SharkFin

Take the BEBL Challange!

2009-10-31T12:43:00.001-04:00

In order to encourage people to make the BEBL, I am offering $35 to the first person to build and demonstrate a functioning BEBL system. That should be enough to cover the cost of the electronic components.

To claim the prize, post a video on line of your accomplishment demonstrating functionality both on and off the bike. The video should include close-ups of the completed hardware. I will address any assembly questions posted here or at Instructables.

Good luck!

The Bar End Brake Light instructions have been made into an instructable and entered into the Arduino Contest.

Jack-o-duino

2009-10-25T11:51:00.003-04:00

Elizabeth and I were inspired this entry in the Instructables Arduino contest. We replaced the servo with a relay to the same effect. It's loud. If we were bomb makers, we'd be dead several times over. Source code can be found here.

Arduino contest at Instructables!

2009-10-13T07:34:00.002-04:00

Keep an eye out for BEBL on Instructables.com. I'll be entering it into the Arduino contest.

BEBL: Updated schematic

2009-09-19T13:18:00.006-04:00

Here is the latest schematic for the Bar End BrakeLight BEBL. Got in the first test ride and it performs amazingly well. The response time seems almost clairvoyant. Ahhh, it feels so good when it stops hurting.

The main change is the power supply fix mentioned in the previous post. The 6V battery I used is this one from RadioShack, but you can find it cheaper on the web. Other changes to note are the power select jumper and the power switch.

The power select jumper allows switching power between the regulated 3.3v from the accel and 5V USB power. This allows the unit to be programmed. The 5V from the USB only powers the micro controller. The 3.3V sensors are therefore protected from the extra voltage. AREF remains connected to 3.3V. I found the switch S2 at Radio Shack. It is perfect. You can access the switch and it stays concealed under the bar. Sweet.

Duh, use the 3.3 Volt regulator on the accel!

2009-09-18T15:24:00.004-04:00

So there was a current issue with running directly off of the battery. I was getting variable readings on the accel when no accelerations were being applied. I'm no EE, so power supplies are a mystery to me. May be the unregulated power was experiencing boom and bust cycles like Wall Street.

Then I remembered the 3.3V regulator on the accel breakout from pololu. Now I run the power right into Vin on the accel and power the rest of the circuit off of the 3.3V regulated output-- fixed. I'd appreciate any better explaination if you know have one.

Now back to the software.

Bar End Brakelight Working... kinda.

2009-08-31T20:07:00.010-04:00

So the hardware on the bar end brake light prototype is complete.

I need to work on the software to get the sensitivity right (solution posted here). The initial code only used one axis of accel data. Better to use two and compare against a floating reference. If an absolute reference (say horizontal) is used, stopping on a hill might trigger the brake light. So more work to come.

I was definitely pleased with the package which slides right into the bar snuggly. I had to shave off some plastic on the DIP socket to get the oscillator to fit. The chipped part above (upper left of IC) is a testament to the snug fit. I used an unregulated 6V mini battery to power the circuit which is the max voltage rating for the Mega. The accel has its own 3V regulator. The accel reading seems to be coupled with the LED on/off state. Maybe I need larger caps on the digital and analog pins. Any ideas welcome.

I use the arduino environment to program the Mega. Below is my development board with the same accel plus a gyro that will eventually go on the SharkFin. After I program the chip, I pop it into the socket on the bar end unit.

Dev Env

This picture shows the unit installed. I found the perfect switch at Radio Shack (see bottom of picture).

Bar End Brakelight

2009-08-22T16:25:00.006-04:00

I've been making progress on integrating the gyro with the accel. When the electronics are done there is still the whole question of packaging! I decided to put togethere a simple bar end break light to get the most bang for the buck early on. Need to add the oscillator and a switch and I'll be up and running.

Here is a pic with a wine cork for size comparison.

And simplified schematic.

SharkFin

2009-07-17T22:13:00.004-04:00

Here is the schematic for a new helmet mounted break light I've been working on. The idea is to measure acceleration and rotation enough to detect breaking from any head angle. Working on the filter now. The prototype is based on the Boarduino from ladyada.net with two breakout boards available from pololu.com.

Improved brake light

2009-07-04T15:23:00.014-04:00

So the brake light was acting a little flaky, turning on over bumps at random. Before, I was using a moving average filter, with ad-hoc checks. I decided to try out a IIR filter because they can produce good results with few taps. This is my first implementation of such a filter.

Infinite impulse response or IIR filters combine measured (feed forward) data and filtered (feed back) data. They get their name because a single non-zero input sample followed and preceded by all zeros can cause the filter to oscillate indefinitely as opposed to a finite impulse response or FIR filter which will return to zero after at most N measurements where N is the number of filter coefficients.

The problem with the brake light was that high frequency jitters were tripping the braking threshold. The only information I really car about is sustained braking, which is low frequency information. I needed a low pass filter, a filter that passes low frequency information and attenuates high frequency information. The Butterworth filter is a low pass IIR filter that is working great for this application.

The filter coefficients are determined by the sample interval, the cutoff frequency, and the number of filter coefficients to use. I chose 2 Hz to be the cutoff frequency. Any lower frequency would delay brake indication, any higher frequency could let in unwanted jitter. I wanted to keep the number of filter coefficients small so that the micro could keep up, It is having no trouble with that; I could probably get away with more filter coefficients, but that delays response time as well.

I was pleased to see how well this filter performed!
I captured this acceleration data riding up and down the street without braking and with. In each image, the raw data is pictured in blue, the filtered data is in yellow, and braking threshold (on the top plot) is indicated in red. As you can see, the raw data is very noisy. The noise is actually bumps on the side of the road, so don't blame the pololu 3-axis accelometer ($17.95!!) breakout I'm using. I purposely aimed for them to make sure the threshold was not set to high which could set of the brake lights every time you hit a bump. With the unfiltered data, it is impossible to set a consistent threshold for turning on the brake lights. The filtered data works though!

The above image just was captured with out braking. I just rode up and down the street without touching the brakes. The threshold was set near the minimum filtered acceleration in the X direction.

This data was collected getting up some speed and braking to various degrees. The X direction is in the velocity direction. Deceleration is indicated by lower X values. You can see the braking go below the threshold even for mild braking.

The Y and Z axis will be used for a future helmet mounted version.

Here is a snap of my data capture setup, thanks to the wave shield from ladyada, and battery and dual proto board from liquidware.com

Here are the filter coefficients, they should work with any IIR filter implantation. The complete BikeLight5 code can be found here.

// feed forward coefficients
double ff[] = {
1.93545410516e-06,
5.80636231547e-06,
5.80636231547e-06,
1.93545410516e-06
};
// feed back
double fb[] = {
1.0,
-2.94973583971,
2.90072698836,
-0.950975665016
};

Arduino on a bread board.

2009-06-07T08:45:00.002-04:00

I've got a couple of ideas for AVR chips freed from the arduino board. Below is my scratch built* arduino. Thanks to LadyAda for posting the schematic for the BoardDuino. Schematic to come.

* By "scratch built" I mean, assembled from the contents of the boardduino kit.

Reuben Margolin

2009-04-18T11:20:00.001-04:00

Watch this video of a Genius at work.
http://blog.makezine.com/archive/2009/01/maker_profile_kinetic_wave_sculptur.html

Wave Shield almost there.

2009-04-18T11:16:00.002-04:00

Lady Ada pointed out R1 was missing, now the SD works! The D2A seems to be the next hurtle.

Arduino Wave Shield HELP!

2009-04-05T10:50:00.006-04:00

I am having trouble with the arduino wave shield by ladyada. I really only need to get the SD card reader up and running. After assembling and programming I get the error messages:

-- Card init. failed! (most of the time)
-- Couldn't open filesys (once in a while).

The 2 GB card is formated as FAT16, with 8.3 filenames. Any suggestions welcome.

MeggyJr Build.

2009-03-15T13:43:00.013-04:00

Evil Mad Scientists

Elizabeth and I wanted an excuse to try out the sweet MeggyJr kit from the Evil Mad Scientists Labrotories (EMSL). She has invented a game called Light and Heavy that MeggyJr will be perfect for.

The kit is fantastic, by far the best electronics kit I have ever built. Extreme care has been taken to maximize your probability of a successful build. The detailed color instructions are included with the kit so you won't have to print those out when the kit arrives. A careful read through before you start might save you hours in the long run, so just do it even if you think you already "get it". Every couple of steps, EMSL include full color pictures of the board so far, which adds reassurance.

If you happen to miss something in the instructions, additional hints are stencilled on the board itself "J1 Other Side" for instance.

The parts are easy to find in ZipLock bags with the step number clearly printed on the outside. And the parts themselves are well chosen and of high quality and should stand up to some hard gaming.

For future designs, I'd like to see sockets for the ICs, they get soldered directly to the board. Also, the way the screen sits the electrolytic capacitor is a bit awkward. They were obviously trying to keep MeggyJr as thin as possible.

When we powered her up for the first time, MeggyJr loaded Attack of the Killer Tomotoes, but the blue LEDs on a single row did not function. Careful inspection of the LED headers revealed scant solder on a couple of the pins which was easily remedied.

That said, how could I have possibly soldered the TTL programming interface in the wrong way? Anyway I did, and to make matters worse, my iron got switched off about the time I discovered the renegade part. So I ripped out all of the vias (through hole copper) along with the part (I know).

So I'm disappointed, but know EMSL were kind enough to provide two programming methods. So I figure, I'll test out the ISP programming header first. This works! and we can compile games in arduino and burn the games using avrdude by hand. As a fall back, it's great.
(NOTE FROM EMSL: First, for the record of folks reading this in the future: DO NOT go deleting the bootloader just because you don't know what else to do.)

So, relieved that all is not lost, I return my attention to the TTL header. Testing the connections reveals that all but pin 5 are not functional. I add jumpers based on the most excellent schematic EMSL have provided.

Now that all connections are in order, I need to replace the bootloader on the processor. I had no idea this would be so difficult! One issue is that the arduino IDE does not automatically work with mega-isp, an awesome adruino script that allows your arduino to operate as an avrisp, and the only way I have to upload the bootloader. It took a while to get the right combination of lock and fuse bits but I finally got avrdude to do the dead. Elizabeth and I literally jumped up and down when we loaded MeggyJr_FroggyJr via the TTL port. Here is the script that finally worked.

#!/bin/sh
OPTS="-c avrisp -p m168 -P /dev/ttyUSB0 -b 19200"
avrdude $OPTS -U efuse:w:0x00:m -U hfuse:w:0xdd:m -U lfuse:w:0xff:m
avrdude $OPTS -U lock:w:0x3f:m
avrdude $OPTS -U flash:w:ATmegaBOOT_168_diecimila.hex:i
avrdude $OPTS -U lock:w:0x0f:m # this was the culprit

COMPLETE!

2009-03-09T21:06:00.002-04:00

Let me know if you have any questions!

Bikelight Schematic

2009-02-23T21:36:00.008-05:00

Here is a sketch of the schematic. It is composed of three pieces: the SPI interface, the accelerometer circuit and the turn signal circuit. The pin names used in the code are indicated on the right.

Amy's Bikelight

2009-02-22T19:11:00.002-05:00

Stay tuned. The brake light accelerometer was hindered by a bug in the arduino pulseIn code, which has been fixed. I also added LED feedback for the turn signal switch.

Emily has taken a couple of videos, that we will post soon.

Amy's New Light Arduino Source Code

2009-02-15T22:27:00.003-05:00

The code for Amy's bikelight can be downloaded here.

Amy's Bike Light Installed

2009-02-10T22:01:00.004-05:00

Here it is! Installed.

Amy's new Bike Light!

2009-02-09T23:01:00.003-05:00

This bike light is made from an arduino, and two LED matrices from SparkFun. An accelerometer controls the break lights and a switch controls the turn signals. More details and a schematic later.

Cycling Shoe Covers

2009-01-03T21:57:00.005-05:00

Emily's feet got cold on our ride the other day so I whipped these together for her. I have to make sure she is ready for the "Cycle of Change" ride for Obama's inauguration. The top is a windproof stretchable fleece. The straps are from an old helmet. They worked great!

arduino Battery Charger

2008-12-24T15:42:00.012-05:00

I was a bit disappointed when I found out my new $150 bike light could not charge itself. Apparently you are supposed to unplug it when it gets warm to the touch, but not to leave it plugged into long because this will ruin the battery! This seemed like a problem for the arduino!

The plan was to use the power from charger itself to power the arduino. This caused a voltage drop of 3 volts, meaning longer charging times. Since I need this daily for my commute, this would not do.

The next version used two power supplies, one for the arduino, one for the charger. This is a bit ugly, but works fine. Both wall warts are plugged into a three way to make it easier to unplug.

The real hurdle was controlling the higher charging voltage with the 3V arduino. The opto-isolator I used initially would not allow enough current to charge the battery. Next was a home-brew isolator that consisted of a photo-resistor and a led taped together. Still not enough current. I finally picked up a 1 A relay from RadioShack. This worked!

The final design uses two LM35 temperature sensors I found on ebay, to compare ambient temperature to the battery temperature. When the temperature delta exceeds 15 degrees F for 10 minutes the charge is considered complete. If at any time the battery temperature exceeds 95 degrees F, power is removed from the battery and no restart occurs.

Here is the schematic and source code. Be sure to wire up the LM35 temperature sensors according to their documentation; if they heat up you have it backwards!

Source Code

Buckyball Adjacency Matrix

2008-07-08T21:53:00.009-04:00

Needed this to create a problem on http://puzzlerace.appspot.com/ and couldn't find it on the web. Here it is (it's all there just copy and paste to your editor).


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300 MPG Aptera Hybrid

2008-06-12T08:15:00.001-04:00

I need this car! Check out this Popular Mechanics review: .

Quantum Erasure

2008-05-23T17:52:00.005-04:00

Please have a look at Emily's slides from the Kids Inquiry Conference. SensL has offered to loan us some single photon detection sensors for our next experiment!

Results

Two Fives

2008-01-12T22:21:00.000-05:00

1. Find the length of the hypotenuse of a the triangle. (1 Point)

Instant Warnings

2008-01-08T05:14:00.000-05:00

Perhaps it is possible to create an instant global (or national) warning network, in case of pending doom (think tsunami). Messages would initiate from a trusted source and would propogate much like an email virus but with source authentication at each transfer. A client program would monitor a designated socket with low duty cycle, when a warning is first received and authenticated, it would log the receipt and propogate the message forward. Subsequent receipts of the same warning would be ignored.

If OLPC is successful, then this platform could be used to support this warning network.

What is this?

2007-12-12T19:28:00.000-05:00

Any idea what this is a picture of?

Ok, so it is a cellular automation, but where did the symmetry come from? Here is the generating snipit of python code.

   def getArray(self):
      if self.count == 0:
          out = random((self.w + 1, self.h + 1))
      else:
          out = self.data[:,:]
          out[:,0]  = 0
          out[:,-1] = 0
          out[0,:]  = 0
          out[-1,:] = 0
          out[1:-1,1:-1] = (out[2:, 1:-1] +
                            out[1:-1,2:])/2.
          out += .01
          i_s, j_s = where(greater(out, 1))
          for i, j in zip(i_s, j_s):
              out[i, j] = 0
      r = out.ravel()
      self.count += 1
      self.data = out
      return out

Hex Clock

2007-12-01T09:04:00.001-05:00

Revolutionary new clock. Forget the binary clock, meet the Hex Clock!

The day is divided into 4096 Binutes, which are sub-divided into 16 tics each. The top three squares display the Binutes Past Midnight (BMP). The bottom square displays 16ths of a Binute, a "tic" which is about 1.3 seconds.

Each side of a square is a bit. The right side is least significant bit, with increasing significance in the counter clockwise direction.

Download

Progess

2007-09-19T21:23:00.000-04:00

Made a little progress on gnuradio today. At least my input matches my output and I've gotten rid of the intermittent response. The decimation of the input needs to be half of the interpolation in order to avoid shifting the frequency. I still to not understand the phase. I am trying to force a phase shift with a complex multiply but the results always seems to be real until I mess with the tune frequency. Hmmmmm

GnuRadio USRP Puzzle

2007-09-07T16:33:00.001-04:00

I think I have a misunderstanding regarding tuning the USRP.

I have connected the TX-A directly to RX-A. I am plotting the FFT of both the transmitted and received signal. I have tuned RX to 0 Hertz so I expect the positive frequencies to look the same up to noise affects.

What I get instead is mostly noise:

Occasionally I get blips of a signal like this:

The GRC graph is also included:

Gnuradio and Gnuradio Companion (GRC)

2007-08-22T20:32:00.000-04:00

Wow,
I've been struggling with gnuradio for a bit when I came accross the gnuradio companion (GRC) written by Josh Blum. This puts the power of gnuradio at your finger tips. The framework is fully extensible too so if something doesn't exist you can create it. GRC has cut my
project time by 4! (see http://www.joshknows.com/)

Check out this screenshot.

Stereo Recording

2006-12-03T22:40:00.000-05:00

Finally I was able to record in stereo thanks to Audacious, an open source sound mixer! I will be using a Lego Mindstorms NXT to cal the microphone at various angles during the next weeks.

dyndns.biz

2006-05-26T23:33:00.000-04:00

Oh man, the sbc is finally back on the web. I lost the dyndns password and had to create a new account.

address wyosbc.dyndns.biz port ??

Logo!

2006-05-21T08:46:00.000-04:00

Andy Duvall of andyduvall.com created the above logo for VisualHearing. After five minutes, I felt like it had been the logo all along!

Baudline

2006-05-14T10:55:00.000-04:00

Had a great conversation with Erik Olsen of SigBlips.com, creator of baudline. Eick expressed an interest in the integration of VisualHearing with baudline. He also pointed out xgl and the Kororaa live cd. The xgl desktop allowes you to set the transperancy on each window. This seems like a great way to overlay different visualizations.

Here is an archetecture that may work with this in mind.


                                   /- Vis1
                                  /-- Vis2
source ---> baudline ---> server < ---Vis3                                             
                                  \-- Vis4                                              
                                   \- Vis5

Got date - local too

2006-05-02T11:01:00.000-04:00

WyoInnovation

The ntpdate syncs the datetime but it displays in UTC format. To show the local date use

tzconfig
Choose America
Choose New_York

This is the default timezone for the machine. Individual user can customize ther time zone using

TZ='America/Denver'; export TZ

.profile is good place to put the above commands

S

SD card partition, filesystem

2006-05-01T22:30:00.000-04:00

Created two ( one to used as DOS, other ext2) partitions
fdisk /dev/sdcard1/disc0/disc

Create ext2 filesystem
mke2fs /dev/sdcard1/disc0/part2

Mount is having problem , giving error
EXT2-fs: blocksize too small for device.

S

It looks like, you can not create ext2 filesystem more than 512 MB on the SD card. Split into two and works

S

1 Gig sd card plugged in.

2006-05-01T18:20:00.000-04:00

Shyama got a 1Gig card for the second sd slot. The new card was found on reboot but not mounted. I guess we need an entry in /etc/fstab??

J

dmesg

2006-04-30T08:38:00.000-04:00

After login, the command "dmesg" will cat the console messages to the screen.

baudline

2006-04-29T14:23:00.000-04:00

Found a great program for visualizing sound called Baudline (free as in beer): http://www.baudline.com. Got it installed on linux box and started playing around with it. Really nice graphics.

ntpdate ntp.org

2006-04-29T14:21:00.000-04:00

Since we didn't spring for the real time clock as part of the SBC we need correct the date each time we reboot. The command is
$root> ntpdate ntp.org

The startup script /etc/init.d/ntpdate already existed. The links in the directory /etc/rcS.d get started during boot with the "start" command. The scripts are executed in order from S00 to S99. I used S51 so ntpdate will run after the hwclock scripts run (and fail).

root$ ln -s /etc/rcS.d/S51ntpdate.sh /etc/init.d/ntpdate

mount CF jump drive (Lexar 512MB)

2006-04-23T20:03:00.000-04:00

I wanted to mount my flash drive which I use in windows. I inserted the drive in USB it displays
Attached scsi disk sda at scsi0, channel 0, id 0, lun 0
SCSI device sda: 1014784 512-byte hdwr sectors (520 MB)
/dev/scsi/host0/bus0/target0/lun0: p1 p2

The fdisk -l shows the two partions, I have on the jumpdrive. Tried
mount -f vfat /dev/sda1 /mnt/flash
It did not recognize the vfat filesystem . It looks like the ARM linux does not load the DOS filesystem related modules ( it makes sense not load unncessary modules). To load the modules

insmod fat
insmod vfat
insmod msdos

mount -r -t vfat /dev/sda1 /mnt/flash
#( -r is for read-only - just wanted to be safe )

ls /mnt/flash

That's it!!

To unmount
umount /mnt/flash

SPM

Logged into sbc wyoinnovations.dynalias.com

2006-04-10T18:40:00.000-04:00

Same user and passwd!

faster boot-up

2006-04-09T19:21:00.000-04:00

disable non-crtical services at startup
update-rc.d -f mysql remove

update-rc.d mysql start 20 3 4 5 . stop 20 0 1 6 . (note the periods)

edit /etc/inetd.conf to disable ftp and telnet ....

eth0 works.

2006-04-09T15:10:00.000-04:00

After I figured out that eth1 and eth0 have different MAC addresses eth0 came right up.

Network is up!

2006-04-08T21:01:00.000-04:00

Used ifup to get the network running on eth1. I'll have to see if the same works for eth0 after I finish marveling at my handywork.

Also used "apt-get install python" which installed python 2.3.

Still need to get the x11 working.

---

2006-04-06T23:40:00.000-04:00

Put the ts-7300 in a large RadioShack project box. Got it to act as a stand alone with keyboard and monitor. Still have not been able to start X yet.

TODO:
Hook up to network
Get X11 working
Pygame/Python installed
Port VisualHearing
Get usb mic and install drivers

Folbot Rudder Quick Release

2005-08-24T20:47:00.000-04:00

To whom it may concern:

I have found this modification to the folbot rudder linkage to be quick to set up without tools and plenty sturdy to stand up to rigorous use. Please contact me if you have any questions. I would be very amenable to any arrangement you might propose in incorporating this into your design.

Thank you,

Justin Shaw