Billysugger:
But if you can live with the pump being on-off only, then switching a ready-made buck-converter will work with simpler software.
Perfect. Yes, the pump is only meant for on-off. I got a DC-DC power converter and did some tests on it with a DC power supply, I got it set at 2.5V output (so the pump doesn't run under full load - hopefully this will make the pump last longer). When I attach all of this to the arduino in the exact same set up (voltage IN coming from port 13 on the UNO board), I get a reading of 0.01V through the converter.
I tested port 13 to a multimeter to ground and when it turns on, it does output 3.6-4.5V (it varies a lot, is this normal?) but then I place the port 13 lead into the voltage IN on the converter and the voltage out reads 0.01V. Not sure what's going on here.
Here are some pics to explain a bit better...
Below - Testing the DC-DC converter. The power supply is set to 4.75V with the positive connector going into "Vin" on the converter. The second pin goes to ground and the third pin in "Vout" which is hooked to the multimeter. I set the converter to 2.5V. Even if I were to turn up or down the power supply, it stays at a very steady 2.5V without adjustment, which leads me to believe it's not a ratio, it's literally just set to whatever voltage I want.
Below - Testing the output of port 13 on the Arduino. It shows 4.5V (but this fluctuates pretty rapidly between 3.6-4.5)
Below - I've set up the converted in the exact same way as the power supply test above, though I've used port 13 as the voltage IN on the converter and it reads 0.01V
Any advice? suggestions? have I done something wrong? I've tested other ports too, just in case 13 had something strange going on. I've also used all different wires, again, just in case...