Making a motion detector

Xyius

I am fairly new to circuits, (I am an applied physics major, I have one year left until I get my bachelors) and I thought it would be really cool to make something that shines a light or something if someone crosses past a sensor. For example, if I wanted to know if someone walks into my shed outside, I could set up one of these and if someone does walk in the door a light in my house would illuminate.

My idea (which is probably pretty naive) is the following..

I saw these "light to frequency" sensors at radio shack, I figured I would shine an infrared laser on it and calibrate it to sound an alarm whenever that signal is disrupted. As far as knowing HOW to do this, I do not know. Is this project feasible for someone with my experience? Where can I get the proper sensors? Does anyone have any circuit diagrams applied to something like this I can study?

Thanks!

vk6kro

That TSL230 chip looks really interesting (and the price is very good too), but I don't think it would help you much. The output is a stream of square waves whose frequency depends on the light level. Turning that into an alarm signal would be an interesting project, but not one I would suggest for beginners.

Burglar alarms use circuits which are like you describe, but they have to exclude all light except the light from the wanted source. This is possible, but not easy. You have to shine the light down a tube which lines up with another tube with the sensor in it. Someone walks between the two and an alarm goes off.

Another way is to have the light source pulsing and then exclude all light that isn't pulsing from the detection.
This gives a better result, but is much harder to do.
Here is an example:
http://discovercircuits.com/H-Corner/40khzlight.htm
not a simple project.

Better projects use PIR detectors and ultra sonic detectors.

Bobbywhy

There are off-the-shelf ready-made motion sensors you could use. Home Depot (or similar) stores sell them as lights that turn on when a person walks into an area. I beleive they function using infrared detectors. But whatever method they use, you can simply remove the lamp and install an adaptor to accept your extension cord. Pass that cord into your house and connect the indicator lamp in there!

Bobbywhy

If you really want to make a DIY project, then you may use one of the following schemes:

Passive infrared sensors (Passive) Looks for body heat. No energy is emitted from the sensor.

Ultrasonic (active) Sends out pulses of ultrasonic waves and measures the reflection off a moving object.

Microwave (active) Sensor sends out microwave pulses and measures the reflection off a moving object. Similar to a police radar gun.

Tomographic Detector (active) Senses disturbances to radio waves as they travel through an area surrounded by mesh network nodes.

http://en.wikipedia.org/wiki/Motion_detector

DragonPetter

You can also look at designing proximity detectors which can give you the same result depending on the situation.

The book "handbook of modern sensors" by Fraden has a section called capacitive occupancy detectors that might be interesting to you. It might be a difficult project to get right, but it is simpler in concept.

zacharyb

Handbook of Modern Sensors is a good read for this, so is "Sensor Technology Handbook" by Jon Wilson should help you as well.

Cheers