@alexhall @TechConnectify I'd also love an Alec take on simple timer circuits and where they show up.

Here's my understanding of Alec's non-microcontroller explanation (in not an expert):

A 555 timer is a simple integrated circuit that can act as an oscillator - turning on and off at a regular frequency. This can be quite fast - fast enough to pulse a speaker and make noise.

He then mentions using capacitors and a transistor and junk to drive the speaker quasi-directly - this could be a reference to using the 555 timer's on-and-off to trigger a transistor that connects 12v directly to the speaker (rather than the 5v the timer spits out).

Then mentioned is a thermal switch - the 555 by itself will just make a continuous noise through the speaker - to make it beep, you need those pulses to stop and start regularly. You could achieve this with a thermal switch - it heats up, disconnects the circuit, then cools down and reconnects, repeat. Or, you could just use another slower 555 timer to turn on and off the first 555 that's making the noise.

Turns out they just used a programmable microcontroller to do all the 555 stuff (make the sound and switch regularly) as they are pretty cheap now, and the MOSFET is the transistor that puts the 12v to the speaker.

I personally love doing things without a microcontroller, it feels so satisfying working directly with the on-off logic.