I’m working on this Polargraph SD machine (basically the prototype for Polargraph SDs to come) for an artist who won’t be able to run “tethered”, so it was necessary to make a little doofer to control the machine.  It works!

This is just two buttons, and three little LEDs on a bit of stripboard, with a little 3D printed case.  The button signals and the LED sources are on pins A1, A2, A3, A4 and A5.  First click engages the motors and sets the position to preset value (i.e. the home point), and then you use the other button to select the command source to use, choosing between USB and SD card.  Then once that’s changed to SD card, and the start button pressed again, then it immediately starts reading its commands from a preset file on the card.

This is a little crude at the moment, and I think the code should be more-or-less rewritten to allow things like pausing and cancel / reset, but it’ll do the job. I don’t think a remote like this will be part of the standard Polargraph SD kit, but a couple of buttons might sneak in.

I’m thinking of the custom board being something like an add-on shield for a Mega / Sanguino, with motor drivers and an SD card reader built-in, but with passthrough headers to allow an offset shield to be added without getting in the way, and using an off-the-shelf LCD+buttons shield for hardware control.  Basically a mega motorshield.  I can’t really decide between a L293D/SN754410 (a la adafruit) setup or a A3988 (eggbot/pololu/stepstick) based design.  Any feelings either way?