Thermal Motion Detector

A "How To..."

                            by Chuck Thurston

Thermal motion is the basis behind most forms of motion detection lighting and security alarm systems.  They use a Passive InfraRed (PIR) sensor, which measures the average thermal energy being emitted by everything within a field of view of the sensor.  If the level changes beyond a threshold limit, either more or less, it detects the change as motion.  So it senses both hot and cold temperature changes.

So for use in paranormal investigations, there's a couple of concerns.

First, having a sensor that has the widest possible field of view, so it covers an area better.

Secondly, visibility.  The sensor will need to be seen by either participants in the investigation, or monitoring camcorders.

So, OK, first let's see about the sensor.  I researched a lot of PIR sensors, and ended up finding this one.  It's perfect for this kind of task.  It has a good output drive, so it can be used to control turning on and off additional red light emitting diodes (LEDs).  It also is one of only a few that have almost 180 degrees of field of view, or half a sphere.  Perfect for covering an entire room.  Oh, and the sensor isn't that expensive, costing only $13.

Here's what it looks like:

and here's a link to where you can buy it:

The PIR sensor has a built in red LED that lights up the dome shield of the sensor, indicating when it has triggered.  But in order for this to be easily seen, it helps to have the output signal of this sensor driving a transistor switch that controls a bunch of red LEDs, just for maximum visibility.  I built mine in a small rectangular plastic project box.  With a red LED on four sides, it has perfect visibility from all angles.

Well, you'll need a few other things, like an on/off switch, a green LED to indicate it's powered, a 9 volt battery, a plastic project box, and... well you get the idea.  But here's the best part.... The Schematic for the entire project:

I made mine for about $50.  So it's not that expensive.  Here's what the final one looks like.

Once you turn the thing on, the red LEDs will light for a while as the sensor adjusts itself to the amount of "background" thermal activity.  This might take up to 30 seconds.  If the LEDs stay lit, there is too much thermal motion for the sensor to see a stable level, so you'll need to either stop moving or relocate the sensor.  After that, the red LEDs will turn off but blink on and off three or four times to indicate it's set and ready to sense any thermal activity.  When triggered by sufficient thermal motion, the red LEDs will light up for about 2 seconds and then go out again.

How to use this is up to you.  It could be used as a response media with a spirit.  "Blink if Yes, No blink is No" kind of thing.  Or left unattended in an unoccupied area, being monitored with a camcorder to record any unaccounted thermal motion.

Probably a future version of mine will be made to fire a flash camera when it triggers.  The ideas are endless  :)   Have fun.


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