By Alex Meaden
This circuit is a simple wire loop alarm that can be used in doorways, hallways, or any other place the tripwire will be broken by intruders. The circuit has a built in siren, but it can be replaced by a relay to drive an external siren, commercial alarm, etc.
|R1||1||100K 1/2W 1% Resistor|| |
|R2, R4||2||10K 1/2W 1% Resistor|| |
|R3||1||1 Meg 1/2W 1% Resistor|| |
|C1, C3||2||0.1uF Ceramic Disc Capacitor|| |
|C2||1||0.01uF Ceramic Disc Capacitor|| |
|IC1||1||4001UBE Quad 2-i/p NOR Gate|| |
|Q1||1||MPSA14 Low Power NPN Transistor|| |
|SIREN||1||Micro piezo siren 12V DC 150mA, 110dB @ 1M|| |
|LOOP||1||See "Notes"|| |
|MISC||1||Board, Wire, Socket For IC1|| |
- The loop can be any type of hookup wire, with a maximum resistance of about 90K. Using very thin wire (40AWG, for example) will make a very sensitive trip wire, but will shorten the distance it can be strung due to the high resistance.
- The siren can be replaced with a relay to drive external loads.