v96 ghetto charger

Posted on Feb 4, 2014

Create a robotic team mascot for my team at work. My first, humble part of that project was to create a charger for the robot`s batteries. I wanted a battery charger that could charge the various NiMH battery packs that I have, ranging from 700 mAh to 2200 mAh and 1. 2 V to 7. 2 V, and be cheaper than the single-purpose chargers sold at the store. I got some

v96 ghetto charger
Click here to download the full size of the above Circuit.

general information about battery charging from and more specific ideas for a charger from. The basic idea for my circuit comes largely from that described on the page above, but I omitted the bridge rectifier and filter capacitor, since I`d rather have a reusable external power supply than build the power supply into the charger, and because I expect my power supply to provide DC rather than AC. I replaced the PIC16C711 and crystal oscillator with an ATtiny13A microcontroller. I added switches to control the charge rate and voltage divider, and to tell the microcontroller what kind of battery pack is being charged, and since I didn`t have enough I/O ports available after adding the switches, I used only a single status LED. Finally, I added a 6-pin header for in-system programming. The rate switch sets the maximum charge rate, 0. 4 amps in the slow setting and 1 amp in the fast setting. The charger software will charge at some portion of that maximum rate. The voltage selection switch allows the battery pack voltage to be selected. The charger is designed for 1. 2V, 3. 6V, 6V, and 7. 2V battery packs, but there is some flexibility and these values could be changed in software. The switch is a double pole rotary switch, which allows it to simultaneously inform the microcontroller of the selection and control a voltage divider to halve the voltage from the battery packs over 4V (since the microcontroller`s ADC can only read...

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