Hi guys,
I bought a few cheap [$1!] battery operated door alarms from the dollar store. I thought there might be some good parts inside.
I took it apart and there is a flat piezo element, a transistor, a resistor and a capacitor, all through hole components. There's an expoy blob, which I think is some sort of IC for oscillation since the alarm "warbles" at 110 decibles. The cool part was a little glass cylinder with tiny metal elements that snap shut when the magnet is nearby. A Reed switch I believe?
Anyway the one thing I cannot identify is a little thing that looks like an electrolytic capacitor, except it has 3 prongs. It was wrapped in black plastic. I cut a bit off with an razor blade and saw that it basically some sort of inductor, it was a tightly wrapped coil of copper wire. My main question is what is this thing called and what is it used for? My guess is this is some sort of inductor that is used to step up voltage/current [I forget which an inductor deals with] to get a louder volume from the piezo element?
I thought it might be a neat project to expand on, say wireless so I can have an alarm in my bedroom etc.