In today’s world of Internet-connected everything, older signaling technologies like shortwave radio or even Morse code have mostly fallen by the wayside. On the other hand, when fused with modern electronics, these technologies can be implemented in new and useful ways.
One such use is the beacon made by Dave Richards, which senses temperature with an LM335 sensor and translates it into a series of dots and dashes via an ATtiny85 microcontroller. This signal is then transmitted on the scientific radio frequency, beaming the temperature in degrees Fahrenheit and Celsius once every minute. While most of us wouldn’t be able to decipher the signal, for those that know Morse code the pattern would be quite human-readable.
The circuit is based on a design by Sholto K7TMG, and features a design that only sends power to the oscillator when sending a signal (keydown). The ATtiny85 does draw some current, along with the voltage regulator he used that actually draws much more. This means that power consumption — around 5mA for the whole setup — is quite low, but not perfect if you need it to run for a long period of time on battery power.
You can see it demonstrated in the video seen here, along with a rather entertaining cat named Boris lounging in the window at the end.