Clock

This is a project that I started after finding this awesome clock on reddit. It seemed like a fun project to learn about embedded systems and a good excuse to finally get a 3D printer.

This is still very much a work in progress but as I progress more parts will show up here.

Progress

CAD

• Motor mounting bracket
• Inner clock hand
• Outer clock hand
• LED mounting bracket
• Organize .scad file for general consumption and small tweaks
• Generate .stl files for all independent parts for printing

Controller

• Decide between Arduino or RaspberryPi
• Would I2C work for this? Can it select fast enough?
• Stepper motor control code
• Game loop style animation library

Open Questions

• I need to be able to reset the position of all the hands so they can align properly to form the digits. How should I do that?
• Would I2C work for this? Can it select fast enough?

Notes

• It looks like the stepper motors I'm using need >900 microseconds between steps, so I need to make sure thats ok. 1ms should be enough to make it work given 2048 steps at 1ms per step is ~2s per revolution which should be fine (it might actually be too fast).
• RaspberryPi supports an I2C bus so that could work to control the stepper motors. The MCP23017 chip is 16 GPIO pins per chip, and there are 3 address ports so I could chain 8 of them giving me 128 total pins. Adafruit has a pretty good tutorial showing how to use it, but they don't explain how to set the correct addresses for multiple chips so I'll have to look into that.
• The current controller circuits I have, ULN2003A, need 4 pins per motor which equates to a whopping 192 pins needed to drive all 48 motors and that's just stupid. Additionally, that's over the 128 pin max with a single I2C bus, so I would need either a second I2C bus or a second RaspberryPi which is even more stupid. That said, I found an interesting article about a circuit that can control stepper motors with a ULN2003 chip using only 2 pins, some resistors and a diode, cutting the total pin count in half to 96 which I can do with 6 MCP23017s.
• I really like the idea of using a RaspberryPi for this over an Arduino because it comes with Wifi for setting the correct time. It also would allow me to write the animation code in python which I expect would be much simpler than using Arduino, if for no other reason than I already know python.