arduino Battery Charger

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

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

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

Quantum Erasure

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

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

Instant Warnings

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.