I always had a trouble to find a partner with a phyphoxed smartphone to reproduce the speed of sound experiment ( https://phyphox.org/experiment/speed-of-sound/ ). And even if you have it you should register the time measured by two smartphones and calculate all... So it would be nice to control the experiment by one smartphone and calculate the seed of sound automatically. I saw the recent forum thread "Device for experimental physics teachers" ( https://phyphox.org/forums/showthread.php?tid=1026 ) using the Arduino nano sense 33 BLE which has a microphone (unlike the SensorTag of Texas Instruments). Perfect to realize the project! Just ask for this particular Christmas gift 
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Instead of a second smartphone the Arduino board can be used. Just to adopt the acoustic stopwatch to it and transmit the measurements by Bluetooth to my smartphone which will do the rest. I have modified correspondingly the phyphox stopwatch in the smartphone. Here are the results. Maybe the programs are not yet perfect but they works. One may remove control communication of the Arduino via serial port to make it completely autonomous. Also a version with 3 claps is possible to realize bidirectional measurements reducing difference of these 2 stopwatches. Arduino sound threshold may be defined by the smartphone as well...
Happy New Year 2021!
Mikhail
The programs for the smartphone and the Arduino nano sense 33 BLE... The extension ".txt" of the latter should be changed to ".ino".
.Instead of a second smartphone the Arduino board can be used. Just to adopt the acoustic stopwatch to it and transmit the measurements by Bluetooth to my smartphone which will do the rest. I have modified correspondingly the phyphox stopwatch in the smartphone. Here are the results. Maybe the programs are not yet perfect but they works. One may remove control communication of the Arduino via serial port to make it completely autonomous. Also a version with 3 claps is possible to realize bidirectional measurements reducing difference of these 2 stopwatches. Arduino sound threshold may be defined by the smartphone as well...
Happy New Year 2021!
Mikhail
The programs for the smartphone and the Arduino nano sense 33 BLE... The extension ".txt" of the latter should be changed to ".ino".