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Step 2Design the Circuit and Lay Out the Board
Here we're building a constant-current battery charger with almost no bells or whistles.
The circuit's straightforward enough. Put a resistor (or group of resistors in parallel) between two pins of a LM317T voltage regulator and it spits out current equal to 1.25 V / R ohms.
The only whistle this cicruit's got, in fact, is the addition of a bunch of sockets which'll enable variable charging currents, which is handy because I've got a bunch of different NiCd/NiMH batteries all with different capacities and want to charge them all.
So first I Googled around a bit, then sketched the circuit out on paper. Next I looked up the pinouts for the LM317 on the datasheet and did a quick mockup drawing on paper with actual-spacing pin-holes, just to see how much room I need on a board.
The circuit's straightforward enough. Put a resistor (or group of resistors in parallel) between two pins of a LM317T voltage regulator and it spits out current equal to 1.25 V / R ohms.
The only whistle this cicruit's got, in fact, is the addition of a bunch of sockets which'll enable variable charging currents, which is handy because I've got a bunch of different NiCd/NiMH batteries all with different capacities and want to charge them all.
So first I Googled around a bit, then sketched the circuit out on paper. Next I looked up the pinouts for the LM317 on the datasheet and did a quick mockup drawing on paper with actual-spacing pin-holes, just to see how much room I need on a board.
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