insideGadgets

The PCBs have arrived for the Small Programmable Power Supply and they turned out well.

And here’s how it looks built up. (I’ve now replaced the blu-tack with some rubber feet)

There was only 1 design flaw to report – for some reason I had thought that one of the digital pot’s pins were grounded when they really weren’t.

I originally looked at the picture when making the schematic it kind of seems like it but I already knew this wasn’t the case as I had built it up before. Something I would have done differently is put in some holes on the PCB for the LM2596 so that instead of soldering the top of the module to the top of the board, you would rather just solder the underside of it.

When mounting all the components, I left the 3.3V regulator’s capacitors to last and powered up the board without them to see what would happen. I found that the ADC reading from the AVR was fluctuating very badly, going from 1V to 2V when the voltage was really 1.74V. Even with the AVR removed, my multimeter was picking up the noise too. When I was going to try the oscilloscope, I connected the ground and then the issue went away. I gave in and soldered the 4.7uF input and output caps and then all issues disappeared, so listen to the datasheets!

I ran some quick tests at 26C ambient and leaving it run for 10 minutes and measured the high point of the LM2596:

• 5.5V at 800mA was 72C, with a small heatsink it went to 68C
• 11V at 1A was 56C

Download SPPS_v0.5, which has a few little improvements regarding the programmable buttons and I swapped the button LEDs around.

I’m looking at ways to include all items as the parcels I send need to be under 20mm height for the low cost shipping of $3 (otherwise it’s like $12-15).

Part 1
Part 2: Added rotary encoder and more testing
Part 3: Back to the LM2596 and calibration
PCBs arrived
Small Programmable Power Supply v1.0 Released