L'Hexapod: The servo controller problems weren't power supply noise...

Previously published

This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.

I’ve been testing the new leg with one power supply for the servos and one for the electronics and all is working well. I expect that all would be working well if I were using a single power supply for both, as long as I was using the new one I soldered up and not the old one…

I decided that since I would be using a 5v power supply for most of the bits of this project that I’d grab and old mains transformer and wire up a 5v regulator and run from the mains rather than batteries. Since this took up a chunk of space on my breadboard I decided to make it a little more permanent on some strip board.


I pretty much followed the Sparkfun power supply tutorial with a little artistic license for the ‘front panel’ and so had a PTC resettable fuse in there to limit the current in case of short circuits, etc. Anyway, it was the PTC that was causing the problem with the servos. It was doing what it should but the servos were trying to pull more current than it would allow and so it was cutting the power (and resetting the servo controller).


Anyway, once I realised what I thought was going on I slapped the multimeter into the circuit and watched the PTC cut out as the servos pulled more current than it allowed.

The new power supply is pretty much the same as the old one without the PTC (I’ll rely on the protection in the voltage regulators for this one) and with a 3.3v output as well as a 5v output.


The servos run fine now and the current draw is within the spec of the regulator. One more small piece of knowledge acquired…