Piezo speakers for Konnected's modules

This minimal electromagnetic speaker emits a high-frequency "beep" when it receives 3VDC.

Can be directly connected to Konnected's NodeMCU board and controlled with Konnected's Beep/Blink handler.

Can be used to mimic the doorbell in many common alarm systems.

The number of beeps, the duration of each beep, and the pause between them can be adjusted. But not the frequency.