It was an interesting challenge to write code which talked to an AS7341 spectral color sensor using Mozzi's twi_nonblock API for I2C communication. I referenced Adafruit's AS7341 library heavily, but I couldn't copy much (any?) code directly on account of the differences between Arduino Wire I2C and twi_nonblock. But twi_nonblock is only supported for AVR chips, and Mozzi runs on additional architectures such as ESP32. Can I get AS7341 to play nice with Mozzi on those platforms?

For my earlier AVR adventures, I laid out my hardware components on a breadboard. This time, with a bit more confidence, I'm going to wire the components point-to-point without a breadboard. Which means I am free to use my breadboard unfriendly ESP32 Mini board and equip it for integrating Mozzi with AS7341.

For Mozzi audio output on AVR ATmega328 Arduino Nano, I wired an earbud headphone directly to pin D9. I was comfortable doing this as the ATmega328 is a fairly robust chip tolerant of simple direct designs like this. However, the ESP32 is not designed for similar scenarios, and I should take a bit of effort to make sure I don't kill my chip. Thankfully Mozzi has a guide on how to connect audio with an RC (resistor+capacitor) filter which should be better than nothing to protect the ESP32 pin used for audio output. According to Mozzi documentation, both GPIO25 and GPIO26 are used. I soldered my resistor to GPIO26.

For audio hardware interface, I used a 3.5mm jack salvaged from a cheap digital photo frame I tore down long ago. (Before I started documenting my teardowns on this blog.) This was technically the video output port with four conductors inside the 3.5mm TRRS jack for composite video, audio left, audio right, and ground. But I only need two of the wires: ground plus one audio signal. The other two wires were left unused here.

For AS7341 interface, I dug up my pack of JST-SH connectors (*) originally bought for a BeagleBone Blue but went unused. This is mechanically compatible with Adafruit's STEMMA QT connectors on their AS7341 breakout board #4698. However, the wire colors in my pack of pre-crimped connectors do not match convention for how they are used in a STEMMA QT. Testing for continuity, I found the following:

  • White = Ground (GND) should be black

  • Yellow = Power (VIN) should be red

  • Black = Data (SDA)

  • Red = Clock (SCL)

I briefly contemplated popping individual pre-crimped wires out of the connector and rearranging them, then I decided this was a quick hack prototype and I didn't care enough to spend time fiddling with tiny fussy connectors. (This is why I bought them pre-crimped!) Hopefully this decision wouldn't come back to bite me later. I soldered I2C data wire (black) to GPIO21 and I2C clock wire (red) to GPIO22. Power and ground went to their respective pins on the ESP32 Mini.

This should be enough hardware for me to start investigating the software side.

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