If you’ve met the folks at Polyglot Programming, you know that we love cats, t-shirts, and wearables. Which is, of course, exactly why we recently came up with an idea to combine all three into a project. No, we didn’t decide to create a wearable for a cat (granted, we gave it serious consideration.) Instead, we settled on the next best thing… a Purr Programming t-shirt with LED lights that can be controlled with a MetaWear board. The concept further evolved to make the LEDs flash and change color when someone tweets to us or mentions our hashtags on Twitter.
For this project, we chose to use MbientLab’s MetaWear R board, some NeoPixels and printed LEDs from Nth Light.
The complete list of parts consists of:
- 1 MetaWear R
- 8 Flora Sewable NeoPixels
- 2 N-Channel Power MOSFETs
- 1 Adjustable Voltage Regulator
- 1 Conductive Thread Ribbon Cable
- 3 Conductive Thread Bobbins
- 1 Purr Programming Shirt
Laying Out the Circuit
Before sewing and wiring, we laid out the circuit. The MetaWear has onboard voltage and can switch low current loads, but NeoPixels and printed LED strips are bright and can draw more power than the board is designed to handle. For this reason, we opted to wire the NeoPixels directly to the battery and used an I2C line to control the strip. The printed LEDs need to stay in a 3V-range (else they will burn out) and are controlled individually by hooking each one to a GPIO pin. Since a LiPo battery operates above 3V, we added a voltage regulator to that part of the circuit, along with a FET to both of the light strips to control them.
Putting it All Together
Sewing requires a certain skill level, but sewing wearables pose unique challenges because you’re creating circuits. Some things to keep in mind:
- Conductive thread has higher resistance than wire. A seemingly short run can add a noticeable amount of resistance that can affect the circuit’s operation.
- Make sure that you use low resistance thread and keep circuit runs short.
- While you can double up your thread in order to lower the amount of resistance, it can make the thread more difficult to work with.
- It’s a good idea to add backing to your design to add stiffness and prevent your circuits from shorting out