About Me

I've been taking things to bits, and making things ever since I can remember, starting with dismantling knackered alarm clocks and watches and helping my dad fix the car. Now I have a well-equipped workshop and have aquired lots of new skills, so I can make better stuff. When they first appeared, I became involved with personal computers, and these and developments in electronics have increased the scope of the things that I can do. Just recently retired, so O yes, now I can make all sorts of stuff.....

Thursday, 8 December 2011

Body sensing stair lights

I'm about to tackle the whole Arduino/Home Easy thing again after a break to finish off some other stuff. As a warm up, I thought I would write up the stair lights that I installed a while back and which would be one of the devices that will be controlled by the Arduino.

I started with two sets of cheap LED deck lights. These are small LEDs encapsulated in a slim waterproof plastic housing and with a stainless steel bezel and clip arrangement. Each light fits into a hole around 12mm diameter and they are designed to be flush-mounted into decking with the lights shining upwards.
I mounted a single lamp on each step, with two on the 'half landing' (I think that's what its called) and one on each side of the lowest step. They come in sets of 10 lights, and I needed a total of 14, so two sets required. I could probably have driven all 14 off one transformer, but I didn't want to risk overloading it so I spread the load across the two transformers that came with the kits.

Fitting the lights was the easy part. I drilled a 12mm hole horizontally into the wooden side of each step, and then drilled another 8mm hole from the top vertically into the wood so that the holes coincided - this let me feed the wire for each lamp into the horizontal hole, then fish it up with a slim hook through the vertical one. At this point I realised what my son Sean had discovered with his hall skirting lights: the lights are longer than the depth of the wood I was fitting them into, so the hole needs to be drilled into the wall behind. Fortunately, in my case the wall is plasterboard, and the extra depth is no problem.

So we now have lights on each step with a pair of wires poking out the top of the side board. On the half landing, there was no wood to fix to, so I fitted the lights to a length of skirting (grooved at the back to run the wires) and fixed the skirting to the wall with NoMoreNails. The lowest step sticks out into the hall, with no walls either side, so I cut a small triangular piece of skirting for each side and fixed these with some stick-on velcro. No other way to run the wires between these last two lights, so I tucked it down in the fold of carpet at the back of the step, and it hasn't reappeared.
Now the hard part, running the wires. I cut a narrow strip of wood the same width as the stair side and around 15mm thick, and cut a groove for the wires into the underside of it on the circular saw. I planned to nail the strip down with panel pins, so deliberately offset the groove to allow space for the pins. I needed two pieces of wood as the stairs are a lot longer than any wood I could buy.

I soldered each lamp to a single pair of wires (lights are wired in parallel) and fixed the wire to the top of the wood with tiny bits of gaffer tape to keep it more or less straight - without the tape, its one of those need-seventeen-pairs-of-hands impossible jobs to fit the wooden capping while holding the wires. The amount of juice carried by these wires is minimal, and the solder joints are all concealed, so I just offset the joints on each of the + and - wires by around 20mm so that they could never touch. You could use shrinkable tubing, but space is pretty tight.

Before covering the wires up, its a good idea at this point to connect the transformers and switch them on to make sure that all of the lights work and that all the solder joints are sound. If any of the lights doesn't work, check that its wired the right way round - LEDs do nothing if they are connected backwards.

I finished off by pinning the strip down (careful not to nail through the wires!) and running a bead of paintable silicone sealer along the joint between the wood and the wall to give an invisible joint.

Now into the home straight. I tidied up the tail end of the wires where they emerged at the bottom of the stairs, and soldered the transformers on to the ends. Plugged them in and switched on, and hooray! everything works!

Not the end of it, though, as of course the lights would then be on all the time. I needed them to only switch on a) when it was dark, and b) when somebody approached ether the top or the bottom of the stairs. After playing with various more complex solutions, I ended up with a cheap and cheerful setup using a Home Easy plug socket and a cheap PIR sensor.

The PIR sensor is designed to switch outside security lights, so it is mains rated and comes in a neat plastic housing which protects the unwary from touching the live wires. Its also has a pair of knobs which adjust the sensitivity and the range of the sensor, as well as the length of time it stays 'on', and the housing swivels as well. With the sensor 'eye' pointing up the stairs at roughly 45 degrees the sensor picks up movement at both the top and bottom of the stairs.

The whole lot is wired in series: the wall socket has the Home Easy socket plugged in, and into this is plugged a short length of 3 core mains cable which goes to the PIR sensor. The output of the sensor feeds a 4 way extension socket block unobtrusively fixed to the wall, and the two transformers are plugged into that.

I have the Home Easy socket turn on each day at around 8pm, and it stays switched on until 7am. During this time, the lights are off by default but turn on when anyone approaches either end of the stairs. The PIR timer is set to keep them on for around 30 seconds, giving plenty of time to navigate the staircase and giving enough light to see some distance beyond the last stair.

The sets of lights were on special offer at around £20 per set from B&Q, and the PIR sensor cost me around £5 from Screwfix (so cheap I couldn't resist buying two, no idea what to use the other one for yet, a classic bargain buy). The lights are one of those widgets that just works, and you take for granted - I only realised how useful it is when my Home Easy remote packed up recently and the lights stopped working.