The motion sensitive light


I friggin' hate plasterboard.

I mean, whoever came up with that as an ideal ceiling material?? Big boards that can hold no weight, damage and disintegrate easily, require a proper plasterer to skim for a professional finish, crack months after that professional finish has been painted, piss out dust when drilled, covers the joists so hanging anything with any weight becomes a lottery, is easily damaged by moisture and in the case of a 1970's house such as mine, is covered with horrible artex which previous owners of the house wrongly figured would be a more attractive finish than a flat ceiling with cracks in.

As if the ceiling in my utility room wasn't crappy enough, the shower waste pipe in the bathroom above became detached and wrecked the plasterboard about two years ago. I had to rip it down so that (if nothing else) I could get into the ceiling void and underneath the shower tray just to repair the pipe.

Heh heh - I remember sticking my fingers up through the shower plughole and pretending to daughter #2 that I had been flushed down there! She was only three at the time - pissed the bed for weeks she did...


So that was two years ago. I wasn't in a hurry to put up a new ceiling because I wanted to make sure the shower was properly repaired and it's sods law that as soon as the plasterer has been paid something's gonna leak and damage the thing again. Finally I came across this Parador panelling stuff in B&Q which is great. Looks much better than plasterboard, is quick, easy and cheap to put up and, importantly, should some panels become damaged because of another leaky pipe, I can simply take down and replace them.

This stuff comes in different colours and finishes so I might end up sticking it in various rooms. It also makes recessed lighting a breeze as the cabling and fittings can all be run in before the panelling goes up.

Ceiling before


I decided to make my own recessed lighting using two 30cm fluorescent battens I already had plus another two I bought from B&Q, some metal edging from Homebase and satin finish glass cut to size by Tamara Glass, my friendly local glazer. I'll need to put some edging around the top of the walls but this sure beats plasterboard!

Now here's the thing. Behind the camera in the picture above is a bit of a dark corner forming the entrance to a downstairs toilet. I figured it would be handy to have a light there to assist with those occasions when it's late at night and I need to drunkenly stumble towards the smallest room in the dark.

In such situations I can't be arsed to switch on all these fluorescent lights - what I want is a small light running from my solar panel installation to activate automatically and illuminate the privvy door in order to guide me in safely!

Cue another Sunday spent bolting together some silly project.

Now this sounds easy. In fact, it seemed to be one of those jobs that wasn't going to be worth writing about. I figured I simply needed to use a standard burglar alarm PIR sensor that I've had on the spares pile for years to switch on a light whenever it detects movement. Where it got interesting was that my PIR has a normally closed (NC) switch contact - i.e. it effectively switches OFF when it detects movement which is the opposite way around to how I needed it.

What I needed was a NOT gate. This would turn an OFF into an ON and vice versa. This is what I came up with:

Motion circuit



The PIR motion sensor has a relay contact that is normally closed - that is to say, when nobody is staggering in an inebriated fashion towards the WC, the switch is closed however the light needs to be off. As closing switches normally turns things on, I need to reverse the operation. I did this by using a BC107 transistor as a NOT gate. The relay in it's closed state allows a current to flow through the 130k resistor into the base of BC107. This turns BC107 on and current flows through the 10k resistor into BC107's collector and out through the emitter to ground. When the sensor detects movement however, the relay opens and BC107 switches off. Current can no longer flow through BC107 and instead it flows through the 10k resistor and into the base of a BFY51 transistor which itself switches on. This allows current to flow through two high intesnsity 5mm white LED's and across BFY51 to ground. When the PIR stops picking up movement, the relay closes, BC107 switches on, BFY51 switches off and the LED's therefore switch off again.

Why these components?? Well, they're just some that I had lying around. Any NPN switching transistor should do however a resistor of at least 10k should probably be inline with the transistor base connections to prevent them being fried. The current consumption of this circuit when BC107 was on (and the lights therefore off) was 1mA (excluding the motion sensor).

To make the thing I used two high brightness white LED's and the reflector from this broken old solar garden spotlight...

Solar light

... and mounted it all on a bit of stripboard.
 
Circuit



The PIR sensor was one I had bought for a burglar alarm project that I never got around to building years ago...

PIR



To make an attractive mounting for the ceiling, I nabbed one of the wife's napkin rings from the dining room (hey, she never used 'em)...

Ring piece



... and after drilling a hole into a plank of the Parador cladding, the ring was glued in using Unibond No More Nails (great stuff!)

Nail it!



On the rear I glued a spare shard of satin finish glass to match the other lights and fitted the board onto the glass so the LED's would shine through.

Fitted circuit board



... and here's the final assembly showing fitted board, sensor and working light.

Finally!



Just to be gratuitous, and because I'm a smug git when it comes to a DIY job well done, here's the finished ceiling (minus edging of course)...

Finished ceiling



It's a thing of beauty - and not a plasterer in sight!

Hang on... does anyone else hear that dripping sound...???