I'd planned a whole thing with the Feather Op Amp Lab yesterday: there was this circuit I built with the original Pocket Op Amp Lab that measured the blood flow through a finger by shining an LED through it and detecting the transmittivity of flowing blood with a phototransistor. The difference in voltage is very small, and you need to add a low pass filter to cut down on some of the noise, but overall it's the perfect application for the Feather Op Amp Lab: a one-chip solution for measuring a subtle analog signal. 

Unfortunately, somehow over the weekend I zapped my OLED wing, and it's no longer working. Which means I couldn't put this demo together in time for submission. 

Nevertheless, I'm tossing my hat in the ring for the Op Amp Challenge, and in so doing, I'm open sourcing both the Feather Low Energy board that drives the Feather Op Amp Lab, and the Op Amp Breakout board that moves those pins to a convenient right angle header area at the right side of the wing. Files are attached to the project, but schematics are included below. 

I'm releasing these as CC-BY-SA 4.0, which means you're free to make your own Feather Low Energy board, and you're also free to commercialize it and sell it. In fact: Microchip? Adafruit? If you want to make these, I would be thrilled to buy some from you. I run a business making objects — Oddly Specific Objects — but after looking into this, I realize I don't quite have the economy of scale to have these manufactured and still hit a price point that I feel good about. I'll likely keep making these boards for me, just because I have client projects and Oddly Specific gadgets that require a low energy, highly analog Feather. 

But if someone wanted to build these, I'd be stoked to buy them rather than having to build them myself. 

Anyway, just to recap the whole entry for the Op Amp Challenge: 

• The Feather Op Amp Lab is a trio of Feather boards designed to explore the analog domain through the integrated Op Amp peripheral in Microchip's SAM L21 microcontroller. It's comprised of three boards:
• the Feather Low Energy, designed by me and open sourced today. 
• a FeatherWing that breaks out the op amp pins.
• and an Adafruit 128x64 OLED Wing
• The Feather Low Energy firmware — open sourced here — displays an interactive UI for op amp configuration, and provides a visualization of the op amps' outputs.
• It's written in a framework called gossamer, which I've also open sourced. This framework aims to be a thin compatibility layer across Microchip's SAM D and SAM L line of microcontrollers
• Gossamer, while a work in progress, is extensively documented, and I hope to use it on more microcontroller projects in the future. 

I didn't get to do everything I wanted to do with this project by the deadline, but I'm still calling it a win in my book: this forced me to finally force Feather Low Energy into the world, and building the firmware in gossamer was a fantastic way to stress test what I've been trying to build there; it gave me a chance to add graphics support and OLED drivers to the framework, forced me to add support for a ton of peripherals, and generally just got me stoked about it in a way I hadn't been since I set it aside late last year. 

So that's Feather Op Amp Lab. And this: