Posted by So I’ve built an IR motion sensor and I originally intended to use the output signal to turn on a lamp or an alarm, but can it be used as a distance sensor? If so, does that mean that, the output signal, the voltage would change depending on how far away the sensor is from a wall?
What I have is called, Ambient Light Ignoring active motion detector. Here is the schematic.
http://www.hobbyprojects.com/quick_circuits_reference/circuits/active_ir_motion_detector.html
I think the two of you must be wrong, because it IS active, because it interacts with the environment. It sends and receives a signal. I tried to look for schematics for IR proximity/distance sensors, and they have the same type of electrical system, just different types of filters and did not have a threshold voltage (so it would measure different voltages depending on distance between object and sensor, if you’re probing after the first op amp, while if you probe the output voltage, it would be either zero, or the voltage given when it "goes high". So third person, please confirm this information.
no, not really. The IR motion sensor just senses motion, it is strictly a passive detector.
No. The active IR you describe doesn’t really detect motion, it detects blocking on the path from the transmitter to the receiver. Dirty emitter or receiver lenses could trigger it. A good use of that type of detector is as a door announcer, or perhaps a detector to open a driveway gate or garage door.