For my Homemade Hardware final project I planned to make a connected stitch counter for knitting and crochet. You would be able to sync the device with your phone to load and interact with patterns. The device has colored lights to indicate where you are in the pattern.
Schematic & Circuit Overview
I used two button switches — one main button for adding rows to your count, and a small button to check what row you are on and reset the count if you hold it down.
I learned to make my own component for one of my buttons. In the schematic I made the symbol a bit large, but it's packaging is accurate. (Shout out to Matthew Kaney for showing me this trick.)
There are 5 Neopixels that change color according to how many times you press the button.
The brains of my project is an RFduino. It runs Arduino code and has a Bluetooth Low Energy (BLE) chip so I can talk to it with my phone.
I am powering the board with a 3 Volt coin cell battery, so I added a holder I could solder on as part of the circuit design.
I chose to make the outline a custom shape so the final product could easily clip onto a knitting project. I think the circle is a really nice shape for displaying the Neopixels, however the end result looks a lot like a Christmas ornament.
Top On the top of the circuit is the two buttons with their respective pull down resistors. The Neopixels also needed a resistor to connect to the RFduino.
Bottom On the bottom of the board is the RFduino, the coin cell battery, and a decoupling capacitor.
Final Traces with Ground Planes
For this project I learned to add ground planes to my board design. This turns the unused space on the board to connect the ground connections. It cuts down on etching and milling time. It can also make it easier to connect traces by offering more surface area to attach ground. In my experience ground traces are the easiest to accidentally rip up, so having a larger space made it easier to fix any issues.
Fabrication & Assembly
Prototype As a proof of concept I assembled this tiny board that I attached to a stitch marker that could clip on to my knitting. Matthew Kaney says it's charming. I left pins to attach this to an RFduino board.
Milling I tried a couple boards with an ATtiny85 before I got my RFduino chips, but they were not successful. I had trouble orienting the Neopixels with the through-hole parts.
Back For this I learned to mill double-sided boards on the Othermill. It was actually pretty intuitive, so I think I will continue on this path.
My traces did not come out great, and because one of my buttons was wired wrong, I had to do a lot of doctoring. I think the newest board design iteration will etch a lot better because I thickened the traces and added a ground plane on the back.
- Re-mill the board
- Tweak the code
- Create a phone interface to load patterns