Data logger for 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 3.6 or newer (tested in Python 3.9 only).

Make sure to have pyusb Python package installed. It ia also recommended to install crc package.

In Debian/Ubuntu: sudo apt-get install python3-usb.

Alternatively python3 -m pip install pyusb crc should also work and get you latest version.

Running

Just run sudo ./fnirsi_logger.py

Data will be printed in real time to standard output. Feel free to save to file using standard shell file redirection or pipe to some other program. Program will exit if the connection is lost.

Format is space separated text file.

timestamp sample_in_packet voltage_V current_A dp_V dn_V temp_C_ema energy_Ws capacity_As
1657568326.775 0 0.00000 0.00011 1.184 1.031 30.500 0.000000 0.000001
1657568326.785 1 0.00000 0.00000 1.184 1.033 30.500 0.000000 0.000001
1657568326.795 2 0.00000 0.00011 1.184 1.030 30.500 0.000000 0.000002
1657568326.805 3 0.00000 0.00000 1.184 1.031 30.500 0.000000 0.000002
1657568326.784 0 0.00000 0.00011 1.185 1.032 30.500 0.000000 0.000003
1657568326.794 1 0.00000 0.00000 1.184 1.029 30.500 0.000000 0.000003
1657568326.804 2 0.00000 0.00000 1.184 1.029 30.500 0.000000 0.000003
1657568326.814 3 0.00000 0.00000 1.188 1.042 30.500 0.000000 0.000003
1657568326.824 0 0.00000 0.00000 1.197 1.060 30.500 0.000000 0.000003

Note: For convenience of using in gnuplot and using shell file append of multiple runs, programs add an empty line before emiting data. This way in gnuplot missing data semantic is automatically detected, resulting in better plots.

For long data logging sessions, it is recommended to use compression, for example:

./fnirsi_logger.py | gzip > mydata.txt.gz

You can also use pipeing to ingest it into other systems, like monitoring, databases, alerting / notifications, or implement extra feature (multi-point calibration, cross device triggers, etc).

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.

Install udev rules:

$ sudo install --mode=0644 --target-directory=/etc/udev/rules.d/ udev/90-usb-power-meter.rules
$ sudo udevadm trigger

This should make fnirsi_logger.py work from any user account.

You can also modify udev rules, instead of allowing all users, allow only users in specific group (most appropiate would be group dialout).

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.

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.

Multiple devices in parallel

It is very easy to add, but I didn't have a use for it. Just open an Issue in GitHub and I will add it.

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.

Also program is simple enough that you can modify it to directly process data in Python.

As an example of data analysis and for convinience, in this repo you fill find a bundled gnuplot sciript plot.gnuplot . If you have gnuplot installed (On Debian/Ubuntu: sudo apt install gnuplot-x11), just run it with ./plot.gnuplot datafile.txt and will output plot.png and plot-iv.png with essential timeseries.

You can call it in 3 forms:

./plot.gnuplot                       # will read live.txt file, and produce png files
./plot.gnuplot otherfile.txt         # will read otherfile.txt, and produce png files
./plot.gnuplot otherfile.txt --live  # will read otherfile.txt, and redraw plot window every 10 s

To do live plotting, in on terminal do for example:

$ ./fnirsi_logger.py >> /tmp/fnirsi-live.txt

and in another do:

$ ./plot.gnuplot /tmp/fnirsi-live.txt --live

Examples:

Hint: The first parameter can be a file or any gnuplot filespec, for example a pipe for decompression: ./plot.gnuplot "<zcat mylog.txt.gz"

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.

FAQ

Will you add ability to write to X, Y or integrate with Z? No. Just write adapter that read the decoded data via a pipe and writes what you need to the system of your choice. It is way more modular, easier to implement, and makes long term maintance trivial. The current fnirsi_logger.py has no dependencies and no configuration. It just works. Adding more would make it harder to use and maintain. (I do have adapter that writes output to InfluxDB, but it is not a part of this project - by design).