But as an added twist, the oscillator is keyed by an ATtiny13 hooked to an LM335 temperature sensor, sending out the Celsius and Fahrenheit temperature in Morse every 30 seconds or so.

However, the temperature sensor’s data is of use to the sports watch in order to trigger an alarm if the temperature rises too high and it’s easily routed via the PDA (node 5).

The temperature sensor is integrated into a small chip measuring 0.15 × 0.15 square millimeters in area. It operates at temperatures ranging from minus 20 C to 40 C.