X10 Motion sensor IR beam mod?


Does anyone have any specifics on doing such a mod? Most IR beam detectors are expensive and rather large. Ideally I would like something wireless (wires between the emitter and detector would be ok).

I was thinking I could just swap out the photoresistor and use an IR emitter. When someone walks between it the motion sensor would think it was dark and act normally. Does anyone know of anyone trying this? or any advice?

I'm trying to automate the lights in my stairway, however the stairway is fairly open and almost anywhere i place the motion sensor it picks up people walking on the lower stairway or walking by and often dosn't pick anyone up. An IR beam at the top and bottom would be ideal.

Any other ideas would be appreciated too, I am however looking for something cheap or homemade.

Any advice is appreciated

I have had decent success with a couple of cheap X10 motion detectors by taping off all but about a 1/4" square hole in the middle of the motion detector window. I used aluminum foil tape. I have one watching my driveway that works well without seeing all the squrrels and rabbits in the neighborhood. Another in my basement never misses when I walk by it. It is looking across a passageway right next to a bathroom door. I wanted to detect when I went down the passageway, but not when I turned and went in to the batchroom right next to the motion detector.
I tried using the photosensor with a laser pointer and it worked, but it was not fast enough, nor reliable enough. I'd be interested in hearing whether or not your mod works.
Such a mod could probably be made but I think it would be rather prone to falsing due to IR "noise". To make it more reliable, some kind of beam modulation would be needed in order to require a specific frequency to be recognized as a valid beam. This is how IR remote controls work. Mind you , looking for the absence of IR (by beam interruption) instead of IR presence might make the noise problem less of an issue.

The other reason for modulation is that to span any real distance, the IR LED would need to output a fair bit of power, which it can't do if its emitting constant IR instead of high powered pulses like a handhed remote is doing. This is what IR blasters do; amplify the IR pulses to high currents through an IR LED.

At its simplest implementation, you would need to send a modulated beam to a missing pulse detector so that very short signal dropouts would not be detected as beam breaks. Both the modulator and missing pulse detector could use simple 555 timers. The receiving timer's output could then provide the signal that the motion detector's photodetector normally provides.
I'm surprised to hear that covering all but a hole of the PIR detector actually works with any reliability.

After looking into it a little more I agree with you on pulses being the way to go. Again i want to keep it simple.
Something like the Sharp GP2D12 would probably work well and its nice and contained.
It should be possible to add this without too many modifications.

I'm still rather surprised I cant find anything like this attempted, as it would be very useful.

I solved my open staircase problem by using a geophone vibration sensor on the botton step. They are very sensitive and it was relatively easy to adjust the sensitivity so that it trigger when someone was on the step vs when someone walked near the staircase.

There was another vibration sensor that I think was from goldmine.com that I recently got for a few dollars to see how it worked. It was not as sensitive as the geophone, but if the stair step is wood rather than carpet it should do the job too.

There are also commercial devices that do a similiar function by sensing the flexing in the floorboards to know when motion is present at that location. The ones I was were rather expensive and comprised of the sensor and a processing module when something like 4 sensor could be connnected to the same processing module.

If you look around you may also find a device used to detect when someone is in bed by sensing the pressure on the bed frame leg. It may also be able to be used if it could be placed under a carpet and the traffic pattern would guarantee that someone would step close enough to it.

For PIR, I know visonic makes units that have a narrow beam and they are fast with only a single pulse needed to detect motion. They are wired/12VDC devices.
AllanMar said:
I'm surprised to hear that covering all but a hole of the PIR detector actually works with any reliability.
I actually drilled a small hole in it where the photosensor was, then I glued a cone in place so that it surrounded the sensor. For the cone I used a piece from a black penholder. I made sure that the length was long enough that the ambient light would not set it off. As I mentioned though, it was not nearly reliable or fast enough to suit my purposes.