PicGoto Voltage Switching

16 Mar 2014.  I built and tested the PicGoto voltage reducer last night.  To recap the issue, PicGoto normally drives the motors at 12 V.  This allows faster slews than the 6 V the original motor driver circuit used, but because it’s using 12 V even when just tracking, the RA motor gets hot.  Reducing the input voltage solves the heat problem, at the expense of slower maximum slew speeds.  Ángel Caparrós on the PicGoto Group recommended another solution, a circuit that uses the output of the LED signal, which comes on only at higher motor speeds, to switch a second voltage regulator between 12 V when the signal is there and 6 V when it is not.  This cost about $5 in additional components.

So I built the thing on Veroboard.  Here’s the layout and a couple of pictures:

I wired this in parallel with the LED signal, and maybe that was a mistake.  I had hoped the LED would still come on normally, but it doesn’t.  Another problem was that I still had to reduce the maximum slew speed from 30x down to 25x (and this hasn’t been fully tested on the sky, so I’m not certain that 25x is working).  The voltage regulator on the new board gets warm, and a couple of times I lost the ability to slew (that might be from overheating, or it might just be the kludgy USB-serial-Windows 7-VMWare-Mac way I’m running it; this is prone to some problems too).   The good news is that the RA motor stays cool as a cucumber.  It would probably be worth trying unplugging the LED to see if that brings the voltage output back up.  I guess more questions to the PicGoto group are in order.