I have a Meade 1206 electric focuser which provides no feedback on position. I automated this by adding a shaft encoder and PID position controller. This allows me to keep the original motor. Here are pictures:
The first photo shows how a plastic pipe coupling attaches the shaft encoder to the focus knob.
The second photo shows the coiled RJ-12 cable which connects the focuser to power and provides serial comm to my scope control PC
The third photo shows the interior.
This was all done with the PIC SERVO Chipset from J.R.Kerr engineering. Generally I used the same circuit they sell in their evaluation board. The part I added was a Borland CBuilder windows application to provide coordinate display, step in step out, hard stop detection, presets, etc. The resolution is in 512ths of a focuser knob turn. With the 1/4-20 thread used by Meade this means the steps correspond to about 2.5um mirror movement each.
NEW!!! 5/2002 - Thanks to some fine coding by Dave Allmon the focus control program supports the ASCOM focuser standard. This allows it to work with Larry Weber's Excellent FOCUSMAX software. Here is a screenshot of the software in action. Click picture for full image.
