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Hardware
I decided to go with the "Pi" family of single board computers rather than the Arduino family. I find the Pis to be easy to powerful, easy to program, and not much more expensive that Arduinos. I used an Orange Pi Zero. I liked the fact that it had Ethernet as well as WiFi built in. Plus, it was cheap (like me). You could probably also build this project with a Raspberry Pi Zero W, or a Raspberry Pi Zero, or even a full Raspberry Pi 3. Really what you need are:
- A card that can run some flavor of Linux
- GPIO pins in the standard 2x13 format of the Raspberry Pi
- A USB port
There are two main pieces that the processor has to talk to - the display and the encoders. The display is a 3.5 inch touchscreen that plugs straight onto the GPIO pins of the Pi. The encoders use a GPIO expander board from Adafruit which connects to a custom PC board with the encoders mounted to it.
- Orange Pi Zero from Aliexpress
- 3.5 inch TFT touchscreen LCD module
- Knob caps
- Extra tall stacking header
- Adafruit GPIO Expander Bonnet
- Four rotary encoders
- PC board for encoders - TODO: Add link to PC board design, ordering details
- Two 16 pin headers
- Encoder cable assembly
- Extension cable for display
The encoder board design was done in Autodesk Eagle. The design was sent to (JLCPCB)[http://jlcpcb.com] for manufacture and I had 5 boards back in less than a week. Cost was $6.80 for the boards plus $16.81 to ship them.
The board serves two purposes - physical support for the encoders, and headers for ribbon cable connections. There are two connectors on the board - one for the rotary encoders and one for the push button connections for "clicking" the encoders. I didn't use the second one, but it's there in case I want to use it in the future.