This is my Raspberry Pi 2/3 add-on board for vPiP (Whats vPiP? Its a hanging v plotter control software written in Python and Arduino firmware - it can probably be used for other drawing machines, but its main purpose in life is for use with the vPiP software - https://github.com/brianinnes/vpip).
Update (29/04/2016): Will be continuing testing with the current crop of boards, but have moved master on github to v1.01b which adds a couple of minor fixes and features. Also created a Dev branch for future mods. Currently that includes extra Pi GPIO pins on the SPI/I2C headers and an extra header that breaks out a couple of pins from the Arduino that can be used as a software serial port. Added a picture of the current board in testing to this page.
Update (25/04/2016): Boards are working but there is a comms issue requiring a manual restart of the Arduino for drawings to start. Also a few minor fixes and a couple of changes made for v1.01b on github. Will be continuing to test with the v1.0b boards for now.
Update (19/04/2016): First test batch of 1.0b boards have been manufactured (see pic). Will be assembling a board or two to test everything works as expected.
Update (15/04/2016): There are currently two versions (1.0a & 1.0b), version 1.0b is where efforts are being focused at the moment. It is a HAT spec compliant board but the HAT spec components are optional. Will update when I have some boards to test.
What's a hanging v plotter? Its a drawing machine where a pen is suspended from two strings or chains attached to two motors at the top outer corners of the machine. The pen is moved by lengthening or shortening the strings or chains with the motors.
The hardware is based on http://www.thingiverse.com/thing:1394948 but includes a DCtoDC PSU that should in theory power the Pi as well as everything else.
This is a work in progress, has little in the way of circuit protection, is untested and is more than capable of letting the magic smoke out of your Raspberry Pi so use at your own risk or wait until i've killed some boards and fixed all the problems!
Files are on github - will update this when its tested.