Man page - sense_rec(1)

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Manual

SENSE_REC(1) sense-emu SENSE_REC(1)

sense_rec - Sense HAT data recorder

Records sensor readings from the Raspberry Pi Sense HAT in real time, outputting the results to a file for later playback or analysis. This is most useful for preparing records of experiments for use with the Sense HAT emulator. For example, a recording of a Sense HAT being dropped, a recording of a HAB flight, a recording of the cycle of temperature over a few days, etc.

sense_rec [-h] [--version] [-q] [-v] [-l FILE] [-P] [-c CONFIG]


          [-d DURATION] [-f] output


show this help message and exit

show this program's version number and exit

produce less console output

produce more console output

log messages to the specified file

run under PDB (debug mode)

the Sense HAT configuration file to use (default: /etc/RTIMULib.ini)

the duration to record for in seconds (default: record until terminated with Control-C)

the delay between each reading in seconds (default: the IMU polling interval, typically 0.003 seconds)

flush every record to disk immediately; reduces chances of truncated data on power loss, but greatly increases disk activity

To record an experiment with the Sense HAT, simply execute sense_rec with the filename you wish to record the results:

$ sense_rec experiment.hat


By default, the recording will continue indefinitely. Press Control-C to terminate the recording. If you want to record for a specific duration, you can use the --duration option to specify the number of seconds:

$ sense_rec --duration 10 short_experiment.hat


This tool can be run simultaneously with scripts that use the Sense HAT. Simply start your script in one terminal, then open another to start sense_rec. Alternatively, you can use the shell's job control facilities to start recording in the background:

$ sense_rec experiment.hat &
$ python experiment.py
...
$ kill %1


WARNING:

Be aware that other scripts attempting to use the HAT's sensors will likely obtain different readings than they would have if run standalone. Some of the HAT's sensors are affected by their query-rate, and sense_rec drives all sensors at close to their maximum rate.


If - is specified as the output file, sense_rec will write its output to stdout. This can be used to reduce the disk space required for long output by piping the output through a compression tool like gzip:

$ sense_rec - | gzip -c - > experiment.hat.gz


When compressed in this manner the data typically uses approximately 3Kb per second (without gzip the recording will use approximately 10Kb of disk space per second). Use gunzip to de-compress the data for playback or analysis:

$ gunzip -c experiment.hat.gz | sense_play -


Another method of reducing the data usage is increasing the interval between readings (the default is the IMU polling interval which is an extremely short 3ms). Obviously a longer interval will reduce the "fidelity" of the recording; you will only see the sensors update at each interval during playback, however it can be extremely useful for very long recordings. For example, to record with a 1 second interval between readings for 24 hours:

$ sense_rec -i 1 -d $((24*60*60)) one_day_experiment.hat


Finally, you can use pipes in conjunction with sense_csv to produce CSV output directly:

$ sense_rec - | sense_csv - experiment.csv


Be warned that CSV data is substantially larger than the binary format (CSV data uses approximately 25Kb per second at the default interval).

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March 26, 2024 1.2.2