What do I have sitting around my house that has transistors and LEDs and a button I can repurpose?

One thing I have wanted to do for the Saab for a long time is to add a knock light. The ECU has a pin that goes to ground when the engine knocks, and therefore it is easy to add an LED and resistor that comes on anytime the ECU senses knock.

However, this would only be momentary, and you would have to be looking at the LED to see it happen (you would need a very bright and well placed LED). So I thought back to my digital circuits days in college and thought I might be able to build a latch circuit. Then, I would have the momentary active knock light, and an additional light that comes on and stays on if knock is sensed. The button would be to 'reset' and turn off the light that stays on after a knock is sensed.

The circuit is pretty simple, I need an NPN and a PNP transistor, a few resistors, a diode, the two LEDs, and a momentary button. Yes, I could probably order all this stuff on amazon.

But what is sitting in my house currently that needs to go out to the trash anyway that has this stuff already in it?

The likelihood of you having something old enough to pilfer individual components that are easy to solder to a perfboard is unlikely. Unless you have a bunch of electronics from the 80s or before.

www.digikey.com

www.mouser.com

www.alliedelec.com

Those are the supply houses that people typically order from.

RossD said:

The likelihood of you having something old enough to pilfer individual components that are easy to solder to a perfboard is unlikely. Unless you have a bunch of electronics from the 80s or before.

This, everything from the late 80s or so onward is surface-mounted. I'm not saying you can't take parts from them, but it's not easy.

Anything with two LEDs and a button will likely have the rest in it somewhere. Be warned, the button and LEDs could also be surface-mount components.

ooooh, I do have a very old radio. and I found a magnavox 'standard definition tv tuner'. Why do I keep all this crap.

Maybe  a TV remote?

May have hit the jackpot with that tv tuner.

There are even a couple power transistors it looks like which I may use simply because it will be easier to work with the bigger pieces. Still no button and only one tiny LED though. I think I have some other sources for LED laying around.