During the winter months, there's a group of us that hires a nearby sports hall once a month for indoor flying, and it was here that I noticed some friends using electronic timers with small free flight models. Noticing that these timers were rather fiddly and imprecise to use, I looked around to find the smallest available microcontroller that had Bluetooth built-in - this turned out to be the ESP32 C3 SuperMini, a popular microcontroller module. To create a means of entering flight details, I chose to write an Android app, using the friendly authoring system available at MIT App Inventor - a brilliant resource for anyone who wants to write custom apps for their phone.
Getting to grips with Bluetooth Low Energy, as used by the ESP32, proved to be far more complex than 'Classic' Bluetooth, but the prototype widgit first took to the air in a Veron Cardinal - a classic FF design. From the start, these early flights showed the practicality of the device - after a few test glides, I was able to dial in a short burst of 50% power to extend the test glide - and gradually increase this for longer flights. The function to change motor power over a few seconds helped to smooth out the stall caused by a sudden motor stop - and the ease of use quickly became apparent. After a few tweaks and additions, the Tempo Cardinal motor timer was ready for release. Since then I have used them in several models, including a KK Slicker Mite - which climbs almost vertically under power with a 20g brushless motor and 2s 300mAh LiPo battery.
This timer was intended for use with brushless motors only - it has a problem with DC brushed motors, and was a little heavy for use with the smaller indoor models - hence the development of the Tempo Solo profiler for 1s and brushed motors.