Wireless battery-powered PIR sensor

[JohnW2]

I know this isn't really the right forum but, since I am 'amongst friends' ...

I want to add an additional PIR sensor to my outside lights but practicalities are such that hard-wiring it would be a major mission. I therefore hope to be able to use a battery-powered (maybe even solar-charged) PIR sensor which can communicate wirelessly with some sort of receiver, which I can use to operate a relay which interfaces with the lights. The receiver could be mains-powered, since it will be adjacent to a suitable supply, and the sensor really needs to be suitable for outside use (although I probably could 'shelter' it to some extent).

My searches have not found very much, not helped by the fact that the idiots who invent product names/descriptions very often seem to use 'wireless' to simply mean battery-powered! I've found one or two expensive ones designed to interface with specific alarm systems (hence without an explicit 'receiver'), but not much more than that.

I may end up having to adapt something like a (really!) wireless PIR 'door chime' or something like that, but I can't help but think that maybe the wheel I'm looking for has already been invented. Is anyone aware of any such animal, or something close to it. I'm happy to play with the interface electronics at the 'receiver' end if I have to.

Thanks for any suggestions.

Kind Regards, John

 

[EFLImpudence]

I don't know of a product but could the pir not be mains powered as well? - just saving the cable between the two.

A wireless is a receiver of radio transmissions and the term may not be used for anything else.

 

[rsgaz]

I may end up having to adapt something like a (really!) wireless PIR 'door chime' or something like that,

Well, there's 9v battery powered PIRs...

http://www.alarm-padlocks.co.uk/index.php?act=viewProd&productId=387


edit: Oops, that was the indoor PIR. They make an outdoor model, but only in a Euro version, which is not an issue if you are going to take it apart for the components...

https://www.ultrasecuredirect.com/w...-pin-wireless-intel-socket-004-2140-p104.html

 

[SFK]

John,
So I understand you want a remote battery powered PIR, that controls the mains powered light. if i got that right, They have that at TLC:

https://www.tlc-direct.co.uk/Produc...MIypup49KM1wIVk8myCh3rFwDVEAQYASABEgLfDvD_BwE

The google search I used was "wireless pir and receiver".
sfk

 

[JohnW2]

I don't know of a product but could the pir not be mains powered as well? - just saving the cable between the two.

The problem is in getting any cable to the location I want to site the PIR.

Kind Regards, John

 

[JohnW2]

So I understand you want a remote battery powered PIR, that controls the mains powered light. if i got that right, They have that at TLC: https://www.tlc-direct.co.uk/Produc...MIypup49KM1wIVk8myCh3rFwDVEAQYASABEgLfDvD_BwE

Thanks. That's exactly what I'm looking for, albeit rather more expensive than I had hoped.

Edit: I forgot to add that I'm not sure how/why I didn't find that!

Kind Regards, John

 

[JohnW2]

Well, there's 9v battery powered PIRs... http://www.alarm-padlocks.co.uk/index.php?act=viewProd&productId=387
edit: Oops, that was the indoor PIR. They make an outdoor model, but only in a Euro version, which is not an issue if you are going to take it apart for the components... https://www.ultrasecuredirect.com/w...-pin-wireless-intel-socket-004-2140-p104.html

Thanks, that's interesting, but I'm a little confused. ... I suppose that it's because you've linked to different suppliers, but the outdoor model seems a lot cheaper than the indoor one.

In fact, from your link for the 'outdoor' one (including the other products if one scrolls down), it seems that the indoor and outdoor sensors are both available as separate items, as are the UK and Euro versions of the 'Wireless Wall socket', so it looks as if one can 'mix and match'. The UK socket (at £17.49) is a lot more expensive than the Euro one (£9.16).

If I used either of these, I would have to 'take apart' the Wireless Socket, since it would have to be housed outdoors and I don't want to be doing by the space taken up by 'plugs and sockets', so it would make sense for me to go for the cheaper Euro one. It also looks as if an outdoor PIR with a 30m wireless range (which would be adequate for me) is available which would interface with those for £13.99, so that plus the Euro socket would seemingly only come to £23.15 total.

The one downside of these PIRs is that, as far as I can make out, they do not have photocells, so they will detect motion day or night. However, even if that's true, I could probably live with that, since it will be located in a position where it should very rarely get triggered, day or night. If I were really fussed, I suppose I could add my own 'light control'.

I'll see if I can find out a bit more about these things, and maybe will get one to play with. Thanks again for bringing them to my attention.

Kind Regards, John

 

[JohnW2]

I'll see if I can find out a bit more about these things, and maybe will get one to play with.

An update ... As I said I might do, I have bought an 'outdoor' PIR sensor and a Euro 'Wireless Wall Socket', which arrived today.

It would appear than an 'outdoor' PIR sensor is an 'indoor one' plus a black rubber boot which slips over it!

I will probably provide another update after I've done some playing - not the least investigating the innards of the 'Wireless Wall Socket'.

Kind Regards, John

 

[JohnW2]

Ok. Another update ...

I successfully canabalised the "Euro Wureless Wall Socket" and installed the relevant bits in an enclosure, and it all worked fine (with the wireless PIR talking to it) 'on the bench' (with a small LED lamp as the load). I therefore put it into service, interfacing it with some of my outside lights, and it still works in the sense that the lights come on when the PIR detects movement. However, in the quiescent state (i.e. no motion detected, so lights should all be off), one of the lights, a 12W PAR38 LED, flashes brightly 1-2 times per second (but none of the other LED lamps do).

This device is properly powered (L & N!) and uses a relay to switch the load. It therefore seems that what I'm experiencing (with relay contacts) is similar to what was reported here recently with an ordinary switch (glowing dimly, rather than flashing, when 'off'), I suspect probably due to capacitive coupling. Judging by the assertive reply he gave to that other query ("a new switch will fix it"), I suspect that mwatsonxx would recommend that I could "fix it" by getting a new relay, but I think I'm first going to try an RC 'suppressor' and see if that helps

Watch this space. Any other thoughts?

Kind Regards, John

 

[ban-all-sheds]

Watch this space. Any other thoughts?

Yes - ask watson to buy a new relay for you, for which you will reimburse him if it cures the problem.

He should be OK with that, unless, of course, he knows that his assertion was b*ll*cks.

 

[JohnW2]

Interesting, but it's now seemingly 'sorted' (without replacing the relay ) ......

The 'standard' 0.1μF + 100Ω across the LED lamp reduced the frequency of flashing very slightly, but that's about all. As I increased the value of the capacitor progressively, the flashing got progressively slower and dimmer, but it was not until I got to 1μF (still with the 100Ω resistor) that the flashing stopped completely. Although there may have been some unusual 'extenuating circumstances' in my case (see below), maybe this means that we should be a little more guarded in advising people that 0.1μF + 100Ω ('as sold by Maplin') will 'almost certainly' cure their flashing/dimly lighting (when 'off') problems with LEDs?

One thing I had forgotten is that one of the loads in parallel with this LED lamp (albeit with about 30 metres of cable between them) is the coil of arelay (resistance about 4.5kΩ, but I don't know its inductance). Had that just been a 4.5kΩ resistive load, I would probably have expected it to be enough to prevent the LED misbehaviour (even given the long cable), but its inductance may be making all the difference.

It's a standard 8-pin ('octal' valve base) plug-in 240V relay - does anyone have any idea what its inductance is likely to be?

Kind Regards, John

 

[winston1]

It's a standard 8-pin ('octal' valve base) plug-in 240V relay - does anyone have any idea what its inductance is likely to be?

Kind Regards, John

You could measure it. First measure the DC resistance. Then measure the AC current at 240 volts and calculate the impedance. Pythagorus will give you omegaL There I've almost done it for you.

 

[JohnW2]

You could measure it.

I could indeed. I just wondered whether someone knew the approximate answer to save me reinventing that wheel.

Kind Regards, John

 

[JohnW2]

You could measure it. First measure the DC resistance. Then measure the AC current at 240 volts and calculate the impedance. Pythagorus will give you omegaL There I've almost done it for you.

A further update ...

I did eventually find some figures for a fairly similar relay, but I decided to measure one identical to the one in question, anyway.

Had I done just what watson suggested, I would, of course, have got a very misleading answer. If I had just applied 230/240 volts to the relay and measured the current, the relay would have ‘operated’ and, as we know, the inductance of a relay coil is much higher when the armature is closed than when it is open (see figures below), whereas it is obviously the impedance of the relay coil when its armature is not closed that interests me in terms of the issue in question.

I therefore mechanically jammed the armature, so that it would not move, before I applied the 240V (actually nearly 248V). I also discovered that, despite what I had thought, the DC resistance of the coil was about 8.5 kΩ, rather than 4.5 kΩ I previously stated.

By that process I determined that the inductance of the coil (with armature jammed) was about 87 H, corresponding to a reactance at 50Hz of about 27.3 kΩ. When I allowed the armature to close, the inductance rose to about 137 H (about 42.9 kΩ at 50Hz) - and the latter is the answer that watson would presumably have got.

The overall impedance of the coil (R & L) was dominated by its reactance. With the armature not closed, it was about 28.6 kΩ, and when it was closed it was about 43.4 kΩ.

All my figures based on measurement are quite similar to those I found in the data sheet for a similar (but not identical) relay. For reference, the reactance of a 0.1 μF capacitor (as usually used in ‘suppressors’) at 50 Hz is about 31.8 kΩ.

If I have done my sums right, this does not really explain how large a capacitor I had to use to stop my LED flashing ....

... in fact, as can be seen, the impedance of the relay coil itself (armature not closed) was very similar to that of the ‘standard’ 0.1μF ‘suppressor’ capacitor, so one might have expected the relay coil alone (with no ‘suppressor capacitor) to have suppressed the flashing (although it didn’t).

As shown in the above (and as expected), when one adds a parallel capacitor and starts increasing its value, the (initially primarily inductive) overall impedance (of relay+capacitor) first increases but once one has got to a value which ‘balances’ the inductive reactance, the overall impedance then progressively falls.

However, the above graph (if I’ve got it right) suggests that the overall impedance falls to the same level as that provided by a 0.1 μF capacitor alone when the capacitor value is about 0.2 μF. If, in the absence of an inductive component, a 0.1 μF capacitor usually suppresses the problem then one therefore might expect that a 0.2 μF one in parallel with my relay coil would also do the job - but, as I said before, it didn’t, and I had to go all the way up to 1 μF to stop the flashing (0.68 μF was not enough).

I am confident about my measurements, so the first thing I’ll do is recheck my calculations but, in the meantime, would be interested to hear any comments.

Anyway, whatever the mechanism, my 1 μF capacitor (plus 100Ω resistor) certainly seems to have solved the problem, since the system has been running for a couple of days, never (that I've noticed) with any glimmer of any light when there was not meant to be any, and the PIR does respond to movement as it should.

However, there is one intriguing and bizarre aspect of behaviour of this ‘wireless PIR’ system. I have discovered (thanks to ‘energy monitoring’!) that throughout the period it has been running, in addition to turning the lights on (for the set 3 minutes) when motion is detected, it has also turned the lights on (again for 3 mins each time) every 78 (±1) minutes !!

I was initially unsure as to whether this bizarre behaviour was being caused by the PIR sensor/transmitter or by the ‘receiver’. However, I removed the former from the equation (removed its batteries) this morning and the behaviour in question ceased - so it’s either being caused by the sensor/transmitter or, if caused by the receiver, only happens when a powered-up sensor is in communication with it. Has anyone ever experienced anything like this, or have any thoughts/ideas?!

Kind Regards, John