More PCBs

March 26, 2009

There’s a learning curve. I think I’m past it.
I repaired the busted board. It looks like this:


The so-called second-second-system, using an Atmel168 chip, intended to use Arduino software (minor mods required for lower clock rate), with the option of controlling the LED power profile in software, and also of controlling external electronics.


The pins in a fence around the microprocessor are intended to allow a piggy-back board with additional electronics to be loaded on top. For example, the lights might be controlled independently, or perhaps some rechargeable batteries could be used to provide a standlight, or maybe a USB charger for cellphones and cameras.
Here’s little board to allow a 20+ volt battery pack to be connected or disconnected, under the control of pin B0. Do note, the ability to do battery management is pretty limited — NiMH batteries are finicky, it’s hard to get a good handle on the current going in or out of the battery (10-bit DAC ranging to 5 volts, at best is measuring current through a 1 ohm resistor, with a 5mA resolution. Typical currents will be in the 200mA range, or less, so one part in 40.


I thought about the costs a bit, and had some ideas about simplifying the first board, and arrived at this smaller, simpler board. The shunt comes on a little earlier, but it uses the same ramp-up trick to direct power to the LEDs as the system voltage increases.


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