# IR Aperture

Discussion in 'General Electronics Discussion' started by gladiator98, May 23, 2010.

3
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May 23, 2010
I'm using a disc with a hole in it to stop by use of a stepper motor and IR sensor at the location of the hole. So I was trying to figure out what size hole I need to accurately stop the disc. I noticed that IR sensor vendors list "Aperture Sizes" for the LED and Sensors located within the casing (http://media.digikey.com/pdf/Data ...B Series.pdf). Are the aperture sizes for the LED and/or Sensors the same size that I want to drill a hole in the disc to accurately stop the disc where I want with this sensor? Thank you.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
I really don't understand.

Are you moving the disc using a stepper motor and you want to stop it when the hole is lined up between an IR source and sensor?

If the motion is in a straight line, you may be better off using a slit perpendicular to the direction of travel.

An explanation of what you're actually trying to do may make it clearer for all of us.

3
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May 23, 2010
im making an encoder with an ir photointeruppter and disc

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
OK, so you have a series of holes around the disc and you are using a stepper motor to rotate it?

Is it just one ring of holes, or are you trying to use a series of holes at different radii to determine the current position of the disc? If so, then you should be looking at gray code and stripes painted on a clear disc rather than holes.

3
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May 23, 2010
Well, I'm using a slot cut out of a ring to make a "home position" for a stepper motor. I was needing the smallest diameter that I could make the cut for it to allow the sensor to sense. If the aperture size is 0.01'' for example, then the cut would need to be a little more than 0.01'' I assume?

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
The slot can be quite wide because the stepper motor will not stop between steps (with most drivers).

If you check what the step size is, and make the slot (or hole) as large as possible such that it's not detected when the motor is one step either side of the home position, you should be right.