Motion detectors

We'd need to know a lot more about the specific model. I have motion detectors in my alarm system, they run on 12 volts from the alarm panel.

Thanks, it's the simple 115v outdoor dual spotlight mounted in the eaves. It has a timer setting 1-5-10 minutes on & a range adjustment (max-min).

If you look at the circuitry, you'll find they have a simple power supply that drops the voltage to what they need for the circuitry. If you just replace that with something that is compatible, you should be able to use it. I think in order to provide specific instructions, I'd actually have to see it.

Thank you. I'll send you a picture in the morning daylight. That's direct to your email. I'm one of those who'll benefit from the change in the forum.

John

Well, I looked at the picture, it's not clear exactly how they're powering that, but it's certainly not an isolated supply! Your idea of ringing it out is probably the next step. Are any of those TO-92 devices a three terminal regulator?

I'm away from my play area & won't have a chance to look at it further for a day or two. I am curious to your opinion in general as to the potential practicality of the sensing unit itself (for toy train movements). For instance, if it could be powered easily by low voltage, would it sense movement in the whole room or could it be focused like the Lionel 153 IF?

It's nice that it has a range and timer adjustment. I never tried one of these indoors.

Thank you... John

To tell you the truth, the only way to find out about the sensitivity is to try it. I'd probably recommend a tube over that IR sensor so that it would be directed only to the area in question. It'll surely pick up movement all over the place if it's out in the open.

If you know someone tearing out an old alarm system, those motion detectors are triggered by movement, and they typically run on 12 volts.

new member here, and i don't mean to butt into a conversation, but i just had a fancy security system installed in my shop and the owner of the alarm company spent some time explaining to me how the motion detectors work. maybe some implications for using them on a layout:

- the detectors sense the motion of a warm object. a tire rolled across the shop will not set it off. a cat will. but they are calibrated so that a mouse will not.

- similar with the exterior floodlight motion detectors. a medium size dog walking across the drive will set it off, but they are calibrated so that a bat or small bird will not. many of the floodlight sensors also have a sensitivity adjustment next to the time adjustment.

of course, different manufactures, different models, etc. your mileage may vary. but as far as using them to sense a train passing.... maybe. (better chance with standard gauge than HO ???)
if you do experiment, i'd be interested to know the results. there's got to be a better way to activate crossing gates.

Most motion sensors work by using passive infrared (PIR).
The PIR sensor works by sensing changes in the background IR (thermal) spectrum. So anything with enough heat to emit IR will be detected by the PIR sensor.
I don't know if our trains carry enough heat to be detected.
The only way to focus the IR detected area is through the white lens that comes with the motion sensor assembly. These lenses vary by application. Some are narrow, wide, high, low, etc.
Example: if you don't want your pet to set off the motion detector you choose a lens that blocks areas close to the ground.

I wrote a detailed article on motion detection for model trains that appeared in the January 2008 issue of CTT. There was also a position sensor guide that appeared in the January/February 2009 issue of TTOS's The Bulletin. Be glad to answer any questions.

Looks like I'll have to at least find the CTT article. I might have it?

Thank you, John

Most, if not all, PIR motion sensors have two detectors within the device. The electronics triggers on the difference. This eliminates variations common to both and rejects background or ambient conditions.  For obvious reasons the sensor is oriented on the board to detect lateral motion which works for trains if you keep the board oriented correctly.

As already pointed out, PIR sensors look for changes in heat.  An engine can trip the sensor because the electronics warms the chassis. But back up a room-temp caboose or rolling stock past the detector and less joy…like the rolling tire.

If you turn on the module with an engine blocking the module, it probably won’t trip as it looks for changes rather than some minimum level of IR (motion detection vs. occupancy detection).

I’d be curious if you can directly connect this to auxiliary 14V AC and drive an accessory.  So if they use triacs (rather than a relay) to switch the lights, the output side might be good to go…albeit the accessory may need to be non-inductive to keep the triacs happy. Which goes to gunrunnerjohn’s question about if/how the line voltage is converted to 12V DC or whatever to power the electronics.  If only one or two components need changing to take 14V AC (instead of 120V) on the input side, I think you’ve discovered a nice hat trick for AC-powered O-gauge accessories.

If experimenting with a shield, tube, or whatever to reduce the field of view, materials opaque to the human eye might pass “invisible” IR just fine. The multi-faceted translucent white lenses you see on motion sensors are plastics engineered to pass IR.  At the risk of being a party pooper,  I think it a challenge to make an IR “lens” that maintains the left-plane, right-plane separation into the sensor window with an effective focal length of a few inches or something equivalent to a Lionel 153. But with some persistence I think you can get something to work.

In some outdoor motion lights a quick ON-OFF-ON forces the output ON which might be a useful manual-activation feature for an accessory.

While all this may be covered in the CTT article, please post any photos and your results.

IR detectors do not use heat. They use a focused beam of light which is just below what our eyes can detect, just below the color red, hence the term infra-red. There are two types. One contains both the emitter LED and the detector photo-diode and bounces the beam off the train. The other has the emitter on one side of the track and the detector on the other side and the train interrupts the beam signalling the dection circuit. Be glad to add more if needed on this subject.

Every object or person with heat emits infrared radiation. Ever heard of FLIR? Forward Looking InfraRed? AKA thermal imaging? It works by detecting IR emitted from heat sources and displaying it on an convenient screen. Makes it real easy for our troops to spot enemy snipers at night. Passive InfraRed (PIR) is used for security system motion detectors. With PIR the IR sensor takes a "snapshot" of the all the detectable IR radiation within its view. When something moves into the sensor's view that changes the IR "picture," the alarms goes off. Then the sensor resets and takes a new picture.

You are confusing passive infrared with an infrared transmitter/ receiver. The detector being discussed here is a passive device which others have explained senses changes in the area being monitored.

The principle it's based on is that everything above 0 degrees Kelvin emits some level of IR. even a tire rolling across the workshop emits IR. If you take the cover off a PIR you will see a multi-faceted reflector which has different passive zones, and any change in IR energy from one zone to the next creates a change of state. Sensitivity control, either preset or adjustable, will usually eliminate false alarms.

The priniple I described is for motion detectors intended for model trains, not infra-red imaging. Model train IR detectors work the same as your TV remote control. You need to have an emitter and a detector. I have used every type of IR detector from various manufacturers (Z-Stuff, MTH, etc.) in my layout and they all work reliably.

One is a passive infrared detector, the other is an infrared opto-interruptor.  They have infrared energy in common, but work in completely different ways.  For simple train detection, the PIR is overkill.