usb-multimeter 3.0.0

Fork of fnirsi-usb-power-data-logger

Data logger for JT-UM120, FNIRSI FNB48, FNIRSI C1 and FNIRSI FNB58 USB power meters

FNIRSI FNB48, FNIRSI C1, FNIRSI FNB58 are cheap and relatively good USB power meters, supporting various charging protocols, voltages, and additionally PC communication.

This is a result of reverse engineering of FNB-48 protocol over lazy Saturday.

Requirements

Linux. (It might work on non-linux systems too, but untested)

Python 3.12 or newer.

Installation

python3 -m venv venv
venv/bin/pip install usb-multimeter

Running under normal user (non-root)

Above examples showed running with sudo (root user). This is because these USB devices are of HID type, and not standard serial devices. You can manually change permissions of them with something similar to sudo chown $USER /dev/bus/usb/001/030, or better yet, install udev rules as described below.

Create USB group:

sudo addgroup usbmeter

Install udev rules:

sudo install --mode=0644 --target-directory=/etc/udev/rules.d/ venv/lib/python3.12/site-packages/usb_multimeter/udev/90-usb-power-meter.rules
sudo udevadm control --reload-rules
sudo udevadm trigger

This should make fnirsi_logger.py work for users of the usbmeter group.

Accuracy / resolution

Time - few ms. By default samples every 10ms (technically 4 samples every 40ms). Time is printed as UNIX epoch in seconds, with 1ms resolution.

Voltage, current - all printed decimal digits. 0.00001 unit.

Temperature - device resolution is 0.1°C, but a low pass filter is used to smooth it a bit, and output with 0.01°C. Less than a second delay expected. As far as I can tell negative values for temperature are not supported, it will report close to 0°C. Temperatures in range 0–70°C were tested.

Energy and capacity - all printed decimal digits. Note: Device does not send energy and capacity. Values are integrated (from power and current) on the host instead. They do start at zero at program startup.

Note: It is expected voltage are positive, if not Energy and Capacity might go backwards!

Note: Power is not provided in the output. Just multiply voltage and current values to get power in Watts.

Supported devices

FNIRSI FNB48 and FNIRSI C1 are known to work. It will use first that it finds.

FNIRSI FNB58 is also known to work, thanks to work of @didim99.

FNIRSI FNB48S should also work.

JT-UM120 are known to work.

Make sure to have relatively recent firmware. My FNIRSI C-1 came with very old firmware (0.20) that did not work out of the box, but upgrading to the latest firmware (0.70) made everything work with exactly same code.

Built-in storage

Some meters do have small FAT partition that a metter can log to, and then read back on a computer as a simple storage device. A format is simple binary format called CFN. There is a tool at https://github.com/didim99/usbmeter-utils to read it and convert to CSV.

Data analysis

You can do whatever you want, it just simple text data that can be feed to file or a pipe. Import to program, spreadsheet, Python, R, Octave, gnuplot, export to InfluxDB, Prometheus, Kafka, MQTT. For quick and dirty work, one can use awk, sort, or my command-line program kolumny. There are no limits.

Limitation

All values seems to be correct. No extra calibration curves are used, as device sends values that already have device calibration applied.

Program uses fixed sampling rate of 100 samples per second (highest avilable). If you want lower sampling rate, just skip some output lines. In gnuplot to speed up very long (days) logs, use every 10 for example, to skip lines automatically. If you really need lower sample rate, open a GitHub Issue about it. For now you can use something like ./fnirsi_logger.py | awk 'BEGIN {next_t=0.0;} { if ($1 >= next_t) { print $0; next_t = $1 + 1.0;} }' to limit output to 1 sample per second.

TODO

FNB48: Sometimes on program exit, the power meter display gets frozen.

Note: This is now partially fixed (when we exit, we make sure to read all the data before actually exiting - this way power meter does not fill up its internal FIFO buffers, and block forever). Partially, because sometimes meter still gets stuck. Waiting a bit, and reruning script few times, sometimes bring the device back to life. If everything fails, replug the device to reinitialize it.

It might make sense to add triggers (configured via command line options): when to start outputing data (i.e. when current goes from low to above 20mA), and when to stop outputing data and exit (i.e. when current goes back to below 10mA for 60 consequtive seconds). It is easy to add, I just do not have much use for it personally.

Power Delivery type detection does not work.

Firmware update still requires Windows. Running in qemu / virt-manager, and doing USB redirect works for this purposes. Unlikely to be implemented.