pull alarm help - Electronic Circuits Projects Diagrams Free

fairlight · 21st October 2009, 02:56 AM

I'm trying to reproduce a pull alarm from radio shack. I took it apart and followed the lines with the beep setting on the multimeter. The silicon black spot was scratched off with a razor blade. Unable to tell how it was connected inside there.

I think have got as far as possible for myself and need some assistance. What exactly is the bottom round thing with three connectors? I was thinking a capacitor of some sort. The red wire is bent and only connects to 21.

I also want to add another pull section, which was the main reason for disassembly.
The pull part is the rectangle on top.

Here are the pictures.

dougy83 · 21st October 2009, 11:27 AM

Quote:

Originally Posted by fairlight

I'm trying to reproduce a pull alarm from radio shack. I took it apart and followed the lines with the beep setting on the multimeter. The silicon black spot was scratched off with a razor blade. Unable to tell how it was connected inside there.

That 'silicon black spot' was the IC that makes the beep signal.

Quote:

Originally Posted by fairlight

I think have got as far as possible for myself and need some assistance. What exactly is the bottom round thing with three connectors? I was thinking a capacitor of some sort.

the black thing that looks like it has a coil of wire in it would be a transformer (if it has 3 wires), or an inductor (if it has 2 wires).

Quote:

Originally Posted by fairlight

The red wire is bent and only connects to 21.

it connects to the 'pull switch' connector; when the string is pulled out, 21 is connected to the rest of the circuit and provides power for it to screech.

fairlight · 21st October 2009, 06:20 PM

I wonder if the IC can be substituted for a opamp chip or something?
It's probably impossible to find out the part number for the IC. Suitable replacement?

As for getting another pull trigger installed, I may try connecting wires to 12 and 14 to something, ground maybe? Then try another wire connected to 13 as the trigger wire.

Here is a picture of the whole alarm in case anyone recognizes it.

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21st October 2009, 02:56 AM	#1
fairlight	pull alarm help I'm trying to reproduce a pull alarm from radio shack. I took it apart and followed the lines with the beep setting on the multimeter. The silicon black spot was scratched off with a razor blade. Unable to tell how it was connected inside there. I think have got as far as possible for myself and need some assistance. What exactly is the bottom round thing with three connectors? I was thinking a capacitor of some sort. The red wire is bent and only connects to 21. I also want to add another pull section, which was the main reason for disassembly. The pull part is the rectangle on top. Here are the pictures. Attached Thumbnails Last edited by fairlight; 21st October 2009 at 02:59 AM.

21st October 2009, 06:20 PM	#3
fairlight	I wonder if the IC can be substituted for a opamp chip or something? It's probably impossible to find out the part number for the IC. Suitable replacement? As for getting another pull trigger installed, I may try connecting wires to 12 and 14 to something, ground maybe? Then try another wire connected to 13 as the trigger wire. Here is a picture of the whole alarm in case anyone recognizes it. Attached Thumbnails