Cyntech do a word clock - an 8x8 array of neopixels, a set of acrylics to make a box and stencils for the words and space to fit in a pi zero or pi 2/3 inside. It’s been built here for a while and suffering from random light shows on the display and dropping the WiFi.
Well the light shows were down The the fact that the neopixels work at 5v but the Pi data line is a beefy 3.3v. Not enough juice means the display data line is susceptible to noise. The solution is a level shifter which bumps the voltage from 3.3v to 5v. I used a 74ACHT125 to do this. It’s capable of shifting 4 lines but I only needed the one.
I laid out the first pass as per an Adafruit tutorial on the subject, with a breadboard. And it worked. The next challenge was to get that inside the case of the clock.
For that, I put an Adafruit permaproto 1/4 size board to task, and replanned the circuit with a single three female header to clip it onto the 8x8 display, then added 3 fly leads to connect to the Pi. I started wiring it up with hookup wire but for fun switched to some 30awg cable which made the process super quick and rather tidier.
And it worked first time…. then I had to put it all back in the box. I hadn’t allowed for the Pi’s USB leaning on some unused tracks on the permaproto board which makes it tilt slightly but its generally all fine and does work. I wonder if my next stop would be getting a PCB design for a super compact version….
It all does beg the question though of why would someone sell a kit which really needs a level shifter. You can hack it with a diode too apparently….
This article was imported from the original CodeScaling blog