Node-exporter textfile collector for Temp & Humidity readings produced from the companion firmware.
Requires the Prometheus Node Exporter to pass metrics to the monitoring system.
The hardware device consists of a Raspberry Pico (RP2040) chip on a board such as the Seeed XIAO RP2040 or the Adafruit Trinkey QT2040, although the exact form doesn't matter. The board layout included here was for the XIAO:
Board layout for Tempmon
The board was designed using DiyLC which was simple enough for this type of project. It was constructed on copper perfboard, using wires soldered to the board all the way.
The MCU board is connected to an AM2320 temperature & humidity monitor using the Pico's I2C bus. Two 3K pullup resistors are required on the I2C lines.
The device also supports an SSD1306-based 128x32 OLED (of which there are many sources), and if present it will show the current readings.
The whole unit is connected to the host PC using the USB serial port, which appears on a Linux host, at least, as /dev/ttyACM?. Consider using the device links under /dev/serial/by-id/
The device firmware is written in CircuitPython (v8), using the SSD1306, neopixel, and AM2320 Adafruit libraries (Thanks Adafruit!).
Although there is a fair bit of exception code it is fairly simple in form: setup the peripherals, then forever loop reading a value, writing it to the serial port and Neopixel/OLED (if present).
The data is written to the serial port as a JSON dict. It is important to the host collector that it is all on one line as the collector relies on the linefeed as a 'packet' separator.
The Seeed XIAO RP2040 includes a Neopixel which the firmware writes a colour to that reflects (very imperfectly) the measurements.
There is no user-configuration available other than by editing the source:
Update the measurement time interval by changing the STEP value (in seconds). Changing it below the time taken to do a complete measurement loop will result in poor results. I suggest a minimum of 1s.
Similarly, adjust def temp_calib() and def humid_calib() as required
for your specific sensor, or have them return the input value unchanged.
The pins used for I2C are usually defined by the board. If you need to do software-I2C use the bitbangio module.
The AM2320 is not marketed as an especially accurate device and has not shown itself to be so... expect values within about 2 deg C and something like 5% RH. I did investigate calibration of my particular device and on that basis the firmware adjusts the returned measurements before passing them on. YMMV.
I have found the relative (minute-on-minute) measurements to reflect reality with more precision, though: a sequence of readings in a cooling or warming environment show that cooling or warming properly.
A simple converter is required to read data from the device's serial port and write it in the correct format to node_exporter's text_collector directory.
A Panel in Grafana showing the results.
The Host collector code is ironically more complex than the firmware,
becuase it has to report samples whether or not info is coming on the
serial port, or even if there is no port! This is so it can report the
'up' value, showing whether the data source is present or not.
Most of the reader uses a Stream object to represent either PySerial or a normal File source, but the stream is either for File or PySerial selected by command line option -T for PySerial.
Data from the serial port is read in as it comes into a buffer, and once a whole line is available in the buffer that is extracted and parsed as Json. The JSON dictionary is then written to a new text file using wr_param(), and the whole process restarts.
usage: tempmon_collector.py [-h] [-i PORT] [-T] [-b BAUD] [-o PROMFILE] [-O]
Serial-to-promfile converter for TempMon gadget. See the Prometheus 'node_exporter' for details of textfile-
collector promfiles. Locate the output file on a tmpfs (memory) file system.
options:
-h, --help show this help message and exit
-i PORT, --serial PORT
Serial port to read
-T, --tty Treat input PORT as an OS serial port (default to read as a file)
-b BAUD, --baud BAUD Serial port baud rate (only if -T)
-o PROMFILE, --promfile PROMFILE
Full path to promfile to write to
-O, --stdout Write results to stdout as well as promfile
(c) 2023 Ruth Ivimey-Cook
A sample Systemd Service file is provided, which works for me! You should as a minimum ensure it is calling the collector with the correct device file.
The node_exporter listens on HTTP port 9100 by default. See its --help
output for more options. One of its options is for a textfile-collector
directory, which if present it will scan for input and when found,
pass on.
By writing a file into this directory in 'Prometheus-metrics' format, you can thus include it in the node_exporter output.
Because the files in this directory are rewritten very frequently and
they are also ephemeral, it is best to put it in a filesystem using the
tmpfs filesystem, such as /var/run/node_exporter/textcollector.
The promfile created will look something like this. The name prefix (here 'airtemp_' can be changed using the prefix variable in the source.
# TYPE airtemp_info gauge
airtemp_info{name="tempmon",version="1.0",tty="/dev/ttyACM0"} 1.000
# TYPE airtemp_up gauge
airtemp_up{} 1.000
# TYPE airtemp_temp gauge
airtemp_temp{unit="C"} 18.000
# TYPE airtemp_humidity gauge
airtemp_humidity{unit="%"} 47.900
# TYPE airtemp_uptime gauge
airtemp_uptime{unit="s"} 1728.000
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Currently the in the Collector the File source (no -T) is broken because readline_partial() wants to use .in_waiting, which is not present for Files.
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There is code to read 2 buttons, and one button on the board, but so far nothing is done with these. Eventually they will be used to enable/disable the CIRCUITPY mass storage device, and possibly to set the OLED display mode.