Alarm DIY time.  - Page 1
Forum section: electronics / beginners

author: Dazza101
author_rank: Newbie
timestamp: May 13, 2019, 01:54:19 pm
content: Hi guysI’m raging at myself for not being able to work this out so have come here to seek some expert advice.So basically I have a 12v battery, 12v switch, a 12v PIR Motion detector and a bloody loud 12v siren.So I wire it all up, nothing crossed and turn it on. Alarm goes off, I think happy says at least it works, after 15seconds the alarm stops, result it’s armed and works. However if I go into shed/work shop I turn it off do what ever I have to do,then turn on alarm using outside switch ( hidden) it goes off. Before resetting itself.Now that 15 seconds of siren wouldn’t be an issue if I lived in the middle of nowhere but I don’t and neighbours will soon get cheesed off...So I’m either looking for PIR switch that doesn’t power up circuit on power up, a second amazon special does the same thing as the first, just like a halogen security light when their powered up. Do it might be the norm?Or a something else that relays the power from PIR for power up but will allow power to reach siren after a set period of time.I hope that makes some kind of sense, so in a nut shell, how to stop siren from coming on on power up?Thanks...

author: StillTrying
author_rank: Super Contributor
timestamp: May 13, 2019, 02:21:44 pm
content: Leave the PIR always powered, and switch just the connection to the sounder ?

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 13, 2019, 03:28:56 pm
content: Publish the model, make, photo or something of your sensorI think these things latch on... and then take a while to reset... ?

author: 66cccfff
author_rank: Newbie
timestamp: July 11, 2022, 02:16:12 pm
content: An H3Y-2 time relay would work. Connect pin 14 of the relay to +12V, and pin 13 to GND, and connect one of the NO contact with the siren in series. Set the delay time to about 20 seconds.Then once you power up the system, the relay contact will keep open in the first 20 seconds and then close automatically. That prevents the siren to ring when the detector prepares itself.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 11, 2022, 02:24:43 pm
content: Just have 2 switch. One to power the PIR and the other to disconnect the horn to the PIR. So just turn the PIR on first wait for it to reset then connect it to the horn via the other switch. It's much easier. If you want 1 switch I would rather find an PIR unit that doesn't turn on the sounder everytime you enable it for 15 sec.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 11, 2022, 11:08:58 pm
content: Just forget it.Those cheap PIR sensors are not fit for blaring alarms. They have far to many false positives, from "real events" such as animals passing by or gusts of wind (especially with summer evenings when it's cooling down quick) to other events such as electrical interference. Those cheap PIRs are barely adequate for outdoor lights. Nobody cares if those switch on 10 times a night because of some moving tree branches.There are better sensors, (also in PIR variant) but those are probably in some other price range.