What device measures degrees/radians from a zero point?

Question

I'm trying to find a device that measures degrees or radians from a 0 point in a circle. For example, you have an arm that rotates in a circle around this sensor - I want to be able to read out what angle this arm is at, at any given time.

Answer 1

This is called a rotary or angular encoder. Google it and you should get lots of information on them.

You could make a rough optical one with leds and a photodiode circuit. You make a disk and cut various slits in it so that for a range of angles you can have only one possible combination of slits.

Check this image from Wikipedia:

http://en.wikipedia.org/wiki/Image:Encod...

So the white spots are where the light can pass through and the black blocks the light. Then you arrange a row of LED's radially on one side for each radial segment (in this case 4) and a set of photodiodes on the other side with whatever type of interface circuit you want. When the light passes through the white parts and reaches a photodiode it will allow a current to pass through the diode. In this way you get a digital signal representing the angle of the encoder.