Alarm Power Cut-Off Circuit

On 2006-06-30, snipped-for-privacy@googlemail.com wrote:

yes, splice this into wires running to the siren, it'll do what you ask. _o-------------> to siren from alarm 12V DC _-~ >---------+---+--------+---------------o~ : o--- | | | _:_ | | | .-------|\\ | relay coil resistance ===== | . . . .|. . . . | | \\ | more than 60 ohms 220uF | | . VCC(8) . | .--| \\| | | . . | | ~~~ | +-RES(4) OUT(3)---+-| | . . | +->|--+------TR(2) CV(5)-- | | | . . | | / . GND(1) . | | \\5.6M . . . .|. . . . | | / | | | | | | >----+-----+------------+-------------+ the diodes are 1N4000 (or similar eg 1N4004) With the components shown you should get about 20 minutes delay before it cuts off. (you can test this with the siren disconnected) pick a relay with contacts rated for the current the siren draws, an automotive horn relay should be suitable (I think they have coil resistance about 120 ohms) but you can probably get by with a smaller relay,

use an bipolar 555 like NE555 or LM555 not a CMOS part like TLC555 or LM7555 as they don't have the strength to drive the relay

Bye.

Certainly, the 555 should do fine.

By the way, depending on your local laws you may have to have a timed shut-of in your alarm to protect the neighbours. Here in Germany an alarm may sound only for, IIRC, 2 min, unless re-triggered.

This will do what you want:

Yep, my mistake. Took some head-scratching to sort. I had calculated the value, entered it in my simulator, double-checked that the circuit worked, and noted the time was something like 1150 s. But I forgot to change the *schematic* from an earlier value of 1M. In the 'Label-Value' box for Rt's Properties in CircuitMaker I'd entered '4.7meg', as the syntax unfortunately requires, and unchecked 'Visible', so it slipped through.

Well-spotted!