Tuesday, July 17, 2012

Slowly I turned...

It's been a slow summer. I'm still making progress on the bench power supply. It's in the "just get it done so I can move on" phase.

I've got the regulator part of the circuit finalized. I don't think it's perfect, but I think if I ever want to work on something else, I need to move ahead. Since the powersupply has three channels, I plan to have 3 discrete boards.

Here is one of the boards, pre-soldering:
One channel regulator board.
On the left side of the board, there are two PWM'ed input for the voltage and current settings, and two "Vsense" and "Isense" analog outputs that will run directly to ADC inputs on the Atmega 644. The top of the board will have inputs from the ATX power supply at 12 and 5 volts. A variable 0-9V output will come form the bottom-right side.

So in the end, there will be 3 of the above boards, and a master controller board that houses the mcu and io board.

This abomination of a sloppy breadboard is my "working copy" right now. It's got the master control circuit and one channel regulator:

The power regulation part is the upper left quadrant, it's the same circuit as the
perf board above. The rest is the control circuit.

I had a hell of a time denouncing the rotary encoders. I was trying a pure software solution, and it always seemed to not feel quite right. I added some 22nF caps between the encoder outputs and ground and that was the special sauce I needed. I'm quite happy with it now.

I've got most of the code done. I've got a calibration logic coded up, not well tested, I think I'm going to re-do a big part of it, but I want to get the final boards soldered up first.

I still have not figured out how I'm going to house all of these. I thought of using sheet aluminum, but it seems a little pricey at my local hardware store. I'm trying to resist making a wooden case. It would be the easiest, but it feels wrong to encase something that has heat sinks in wood.

I think I'm also going to change the design so that the AVR is always powered, and it controls the on-off state of the power supply. So the AVR will run off of the standby power of the ATX, and I'll use a "soft" power toggle instead of a physical switch.


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