Derive low voltages signal/output from PIR floodlight?

[jg.campbell.ng]

I would like to derive an audio alert from a PIR floodlight. To be more specific: let's say I have the floodlight above a back window and driven from a three-pin plug from inside. I would be happy to bring additional cabling from the PIR.

Or maybe forget that floodlight (I have another outside fed from the garage) and use an external low voltage PIR to feed an audio alert and/or switch on a light (even low voltage). I doesn't have to be DIY; off the shelf solutions welcome!

Just thinking ... I suppose there is nothing to stop me feeding 240V back from the switched supply to the floodlight.

Rationale: I'm interested in being alerted about potential burglaries /before/ they enter; a few nights ago I heard was awoken by burglars attempting to force a window. I assume also, that an audion alert just loud enough to be heard outside might be a deterrent.

I'm sort of reluctant to fit a proper alarm; many reasons, but the main one is that they tend to elart you only after the burgulars have gained entry.

TIA,

Jon C.

[brugnospamsia]

I modified my front door PIR (pre-part P !) to switch a hall light and so I can easily have the flood on continuously :-

what you would use to make the noise I don't know - presumably a transformer and bell / buzzer of some sort ... Actually I have considered doing something similar - maybe something intermittent though in case a neighbourhood cat starts firing the thing off all night ...

[Ben Willcox]

I will shortly be doing something similar, however I will use standalone PIRs to trigger a digtal input to a home automation controller. The plan is to simply use the 240V switched output of the PIR to drive a relay with a 240V coil. Then I can use the relay contacts to do whatever...

The smallest/cheapest relays I could find with a 240VAC coil are about a fiver each from Farnell - a shame as the PIRs only cost me £2 each!

Cheers, Ben.

[Ian Stirling]

The safest and simplest way to do this is to find a 240V relay that will fit inside your PIR device. (assuming you are competant to fit this safely, properly insulated, and secured)

As most floodlights have a choccy block connector in, simply connect the relay coil across the floodlight terminals. Now, you have a switch that goes on when the floodlight does. Connect this to a source of power, and the bell/buzzer of your choice.

[jg.campbell.ng]

Thanks, that looks useful; however, I'm going to have to overcome an irrational (?) lack of confidence in my ability to mix 240V with low voltage equipment (don't comment, I know it is silly and irrational and amateur and non-DIY).

As regards buzzers, I have a (5V?) buzzer and a home made siren from days when I built electronics as a hobby.

Okay, agreed, cats a problem.

A really annoying thing is that I had a 'listening light' socket in the hall until a few weeks ago; suddenly, it started to act strangely, as did two others the same (Unicom??? bought in Aldi -- I posted here to see if anyone could guess why it (actually all three) ) failed in the same way. That would have detected the noise and would have switched on a light, presumably deterrring them.

I assume it would be possible to adjust the 'light level' trimmer on the floodlight so that it comes on all day? (Daytime, it seems to me, being as good as any to commit a burglary.)

Thanks,

Jon C.

[Ian White]

One of the sheds or big catalogues sells a PIR light with a radio link to a 'chime' that can be plugged in anywhere indoors to warn when the light is triggered.

There is a choice of three radio channels, so if you decided to have two PIRs, they could be either be operated as separate systems on different channels, or both set to the same channel so that either PIR would ring both chimes. (As with all low-cost "wireless" systems, the downside is the risk of false alarms if the neighbours had similar devices installed.)

Bought one for the relatives recently, for exactly the reasons you describe, and they are quite happy with it. I just need to remember where from...

[jg.campbell.ng]

Those PIRs work outside? (Or as well as any PIR works outside -- I seem to get no more than two years out of my floodlights, but then they do get the full force of south-westerlies.) You couldn't give a brand namme and/or model no.?

I assume that if I look carefully (online -- unfortunately no store nearby), I can get all this from Maplin?

Many thanks,

Jon C.

[jg.campbell.ng]

What terminals are on that 240-V relay? 240-V (live and neutral) in; two terminals of the switch out? There's not much room left in the plastic box that contains the choccy block connector -- is that where you'd put the relay?

Many thanks,

Jon C.

[Ben Willcox]

Well they are designed to, however I havn't got around to fitting any yet! I can check the make/model when I get home, but they were in B&Q on some kind of sale and I havn't seen them there since. (Other stores might still have them). Ha, found them here in Maplin:

the ones I have are in black. Plus Maplin are ripping people off at that price.

The only relays that Maplin do with a 240VAC coil are big chunky things. Something like Farnell order code 4307719 should do. Of course for your application you ideally want a momentary output, which you won't get with a normal relay so you would need to find some kind of buzzer/alarm that just sounds once when it receives a trigger.

Cheers, Ben

[Mr Fizzion]

Even large hedgehogs trigger my PIR!

Mr F.

[Matt Beard]

Of course you could just connect a "stand-alone" PIR to a 3-pin socket (indoors), then plug in a standard plug-in transformer to give 5v or whatever when the PIR triggers. If you are confident working with low voltages you can build whatever you want to run off this low voltage output.

Do make sure that you properly label the socket though - you don't want the next door neighbour (who pops in to feed the cat/dog/fish while you are on holiday) plugging a hoover in!!

[Harry Bloomfield]

[e-mail] formulated the question :

I have 3x hard wired 500w PIR's and was faced with the same problem. My solution was to find a small tranformer with room to wind a few turns of one of the mains supplies around the core (around 5 turns). I then used the original windings of the transformer to supply a bridge rectifier with a small capacitor across the DC output, to which I then connected a 12v piezo sounder via a switch so it could be disabled. This will need to be the type with a built in oscillator.

The mains cable I chose fed all three lights, so if one PIR is triggered the piezo will sound, more lights trigered equals more noise.

[jg.campbell.ng]

Okay, problem possibly solved.

I bought a 'Jaguar' (IQ Europe Ltd.) 'battery powered PIR sensor with portable chime alert and light adaptor'. (In B&Q, 50 quids.)

Incidentally, initial impressions: (i) I wonder how long the AA batteries will last? (three in sensor, three in chime); (ii) I wonder will the PIR sensor go the way floodlight sensors go when exposed to weather Irish weather (and facing south-west), i.e. fail after two/three years? (iii) cats; I'm now attempting to use some sort of netting to discourage them from their 'traditional route' into my garden; (iv) set off by the onset of bright sunlight; (v) easy to fit and set up -- ten minutes at most -- compared to something that I'd kludge myself.

Thanks all.

Best regards,

Jon C.