i want to know what a coil with 3 connections is.

[Eamonn58]

I am trying to reverse engineer an alarm pizo circuit. Its the loudest I have found with a 9 volt battery.
The circuit has a CD 4069UBE inverter chip with some resistors capacitors transistors.
There is also a coil with 3 connections but I cant find a coil with 3 connectors and don't know what its called. It did have a plastic cover over it (similar to an electrolytic capacitor) which had
something like 865K written on it. I removed it and cant remember the actual number.
I am quite a novice at electronics but realise how useful it is for making cool products.

[langwadt]

tapped inductor?

similar to end of this page, https://itectec.com/electrical/electronic-how-does-the-component-alarm-boost-three-pin-inductor-make-a-piezo-buzzer-louder/

[james_s]

It sounds like a tapped inductor. It's also possible that it has 3 pins but only two are actual connections with the third as a mechanical support.

[Gyro]

It could well be acting as a step-up autotransformer to increase the voltage drive to the piezo. I can't think of any other reasons for having an inductor in a battery operated smoke alarm.


Edit: Oops, as langwadt's link.

[Eamonn58]

Thanks.
Im not sure it makes a difference but it wasnytfrom a smoke alarm but a personal alarm. I want to incorporate it into a car alarm I am making.

[Gyro]

Ah, I must have imagined that bit (probably thinking loud alarms!). No, no difference, it should make it easier to reverse engineer.

[Eamonn58]

Thanks. That looks exactly what it is and it suggests where to get them.
Cheers.