9v school project

A relay is audible with its clicking. The usual 555 output current is around 100-200ma. This is plenty more than enough to power the relay (10ma) and a LED on it(around 7ma, ive had LEDs power with the LS series!). You can see the LED flash on and off and the RELAY click clack. They use them in modems. My one Engineer friend sued this one company (and won) because they were selling these relay systems without debounce systems, so it would constantly click on and off through the Indicator or the lighting. So you would throw the switch and it may turn on or off!

Transistors are purely semiconductor magic. You cant hear the sillicon turn on and off lol.