Shallow Thoughts : : Dec

A Homebuilt CO2 Meter as a Virus Risk Proxy

Despite most of the world deciding that COVID is over, I continue to be cautious about it. (My one bout of COVID resulted in congestive heart failure which I'm still dealing with, so I'm fairly anxious not to get it again.)

That means that I'm cautious about indoor gatherings. Some places say they've upgraded their ventilation, but can you believe them? I've long read about people using CO2 meters as a proxy, to tell you how well the air is circulating and how high the virus load might be in a crowd, and I've wanted to get one of my own.

You can buy CO2 meters, of course. But making a custom one sounds so much more fun! Reading Wired's story about New Zealand's Kawaiicon cybersecurity convention that provided CO2 trackers inspired me to finally order some parts.

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Tags: maker, hardware, python, circuitpython
[ 18:06 Dec 19, 2025    More hardware | permalink to this entry | ]

Crimping JST PH Connectors

(With a cheap imperfect tool)

I've written about the several neat boards I recently ordered from Adafruit.

But when I ordered, I was confused about which connectors were which, and didn't end up ordering all the connectors I needed.

Adafruit calls the connectors they use "Stemma", and (I realized too late) they have a helpful page called What is Stemma? explaining the different connectors. I had ordered several of the small ones, "Stemma QT", more technically a 4 Pin JST SH, which were perfect for connecting a Feather board to a CO2 meter. But I hadn't realized that the bigger board, the PyPortal, needs a larger connector also called Stemma, more technically a JST PH.

It turned out to be hard to find JST PH connectors with wires already attached ("pigtails") and what I found were impressively expensive in lots of two or three. I imagine I might want a fair number of JST PH, especially the 2-connector type used for batteries. So I ordered a boxed assortment of 2, 3 and 4-pin JST PH connectors and a crimp tool.

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Tags: hardware, maker, electronics
[ 13:34 Dec 14, 2025    More hardware | permalink to this entry | ]

Installing CircuitPython on a Gemma M0

(On Linux.)

I wrote previously about my difficulties installing CircuitPython on an ESP32 Feather.

When I ordered the Feather, I ordered a bunch of other stuff too, including a tiny wearable microcontroller that's sold specifically for MicroPython: a Gemma M0.

Again, I had trouble getting MicroPython working, but the Gemma's problem was quite different.

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Tags: hardware, python, circuitpython
[ 18:13 Dec 09, 2025    More hardware | permalink to this entry | ]

Installing CircuitPython on an ESP32 Reverse Feather TFT

(On Linux, natch.)

I've been wanting to play around with CircuitPython for ages. I like Python, I like microcontrollers, what's not to like? Quite a while back, I even ordered a Feather M0 for that — but I didn't do my research, ordered the wi-fi version and it turned out that's the one Feather M0 that can't run CircuitPython.

This time I checked more carefully before ordering, and got a processor that for sure claimed to run CircuitPython.

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Tags: hardware, python, circuitpython, maker
[ 13:58 Dec 04, 2025    More hardware | permalink to this entry | ]