This is a small python daemon (and some sample configuration) that plumbs some environment sensor modules that are suitable for use with a Raspberry Pi to the Prometheus monitoring system, which can log and graph the data.
There's also a script you can run that will display some current values and trend direction on a compatible tiny screen.
This is absolutely a quick hack, to set expectations. But I did document it, so it's got that going for it.
Careful: Two years in I'm hitting the limitations of Prometheus on a Raspberry Pi logging this data:
- The 32-bit version of Prometheus more or less doesn't work on Bullseye, since it tries to
mmapmore things than fit in the address space. Upstream's stance is that this isn't worth fixing (it'd be kinder if they stopped pretending to support 32-bit).- You can still run the older Buster release if you fetch the 2.7 package from the pool, but it too will eventually start hitting address space limits after about two years of data, and start failing in very stupid and dangerous ways: writing constantly to the drive creating broken TSDB updates, crashlooping, and losing all history. It's not clear if the newer version fixes this or not since upstream have a practice of closing bugs as "old, probably fixed?" and describing commits as "fix stuff".
- You cannot upgrade from 32-bit to 64-bit Raspbian. You must install a new image. Until recently, sticking on the tested and universal 32-bit release was recommended.
64-bit Raspberry Pi OS does solve these problems, at least for now.
This is the Prometheus console provided by the default configuration:
You can edit that console template to your choosing, or write a different one, or even go do it via Grafana:
A Pimoroni breakout garden with the right modules plugged in can cycle through some values locally:
- SGP30 air quality sensor (eCO₂, TVOC)
- This one is useful over the other "air quality" sensors because it actually gives calibrated CO₂ readings, even if "equivalent", rather than an arbitrary "quality" scale.
- BME280 (temperature, pressure, humidity)
Note that it does not currently support all the sensors in the Pimoroni Enviro HAT, just the BME280, although it should be easy enough to add (the name is perhaps a little aspirational). I just don't have the hardware to test (or, thus, much inclination). I would suspect that having both this and the code running the display read the sensors at the same time would work poorly, though. If you have the actual hat, it may be easier to hack that to export to Prometheus, than hack this to co-exist.
If you want to use the modules above, it's probably easier to plug them into Pimoroni's breakout garden (there are versions for most Pi variants now). Then everything just plugs together, which is nice.
If you have both the SGP30 and the BME280, the daemon will use the latter to provide humidity compensation data for the former; see section 3.16 of the driver integration guide.
The 1.3" SPI color LCD is what it's written for, but it should work with anything supported by the ST7789 library. There is not support for arbitrary framebuffer devices or anything (but it probably just requires telling PIL to render somewhere else).
See doc/setup-logging.md.
If you have the display as well, then see doc/setup-display.md.
There is absolutely no guarantee I'll ever get to any of this. It's an idea dumping ground. Pull requests welcome though.
- Support more of the environmental sensors, like the relevant EnviroHat ones.
- Allow using the CPU temperature compensation logic that's in the examples for the BME280, for setups that have the board mounted directly over it. (I use a short GPIO ribbon cable.)
- For that matter, implement
vcgencmd measure_tempas an optional sensor, so it can be compensated for Prometheus-side with a computed metric if desired. - Bother to set up the Prometheus console to support multiple instances.
- Suggest some Prometheus alerts, like high CO₂ concentrations.
- Consider doing some refactoring for sensors as a collection of instances of a subclass with register_metrics/init_sensor/measure methods, but this is a little tricksy due to the SGP30/BME280 interaction. Later, if/when there are more supported, perhaps.
- There's no systemd service setup for the display script yet.
Bugs/nits:
- The polling isn't really every second; that's a lower-bound assuming everything else is instant, but there are known
sleeps in the sensor libraries. - The SGP30 baseline is not saved on graceful exit. This probably doesn't matter much since I don't think it's supposed to drift dramatically, so long as you're running the daemon for at least an hour.
Really scope-creepy stuff:
- Log to rrdtool as well, for more suitable long-term storage with downsampling.
- Have a different display script that only shows Prometheus alerts on the tiny panel. For example, have an alert suggest an image and a priority as labels, and if there are any, show the highest one and the metric value, else keep the screen backlight off.
Posters on the Adafruit forums, for pointing out the SGP30 really wants its baseline value saved and restored when monitoring is interrupted, otherwise it takes up to 12 hours to recover properly. The example code doesn't do this, but the library has the methods for it. This used to be really visible as readings plummeting down to minimums on a daemon restart.
Licensed under the EUPL-1.2-or-later. (See GitHub's summary of its terms if unfamiliar. It's a strong copyleft open source license like the Affero GPL.)