infared phototransistor issues
I have these infared phototransistors from the local radioshack, and I am having a problem with them detecting all light, and not just infared. They work great, except for that. The problem is, obviously, that it can accept a certain frequency from another (Im having two robots communicate by the way) because all they see is a solid stream of incoming light. I just want to figure out how I'm going to filter out all light but infrared? If anyone has any ideas, I love to hear it!
Thank you,
Justin
Thank you,
Justin
Comments
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Jon Williams
Applications Engineer, Parallax
Dallas Office
Each 'Demodulator' model number supports a certain frequency. Typical frequencies are 36 KHz, 38 KHz, 40 Khz, and 42 Khz. I believe the Radio Shack one is 38 or 40 Khz. The device 'holds' the signal long enough so that a BS2 which sent a pulse through an IR-LED with a "FREQOUT IRPin, Width, 32000 " would be able to read an echo back -- thus allowing its use for collision detection (there's an app-note on this on the Parallax site).
The nice thing about the demodulator is that it does filter out most light, since most light is not modulated at 38 Khz. I don't know about direct sunlight, though. A nice protocol uses a 1 mSec pulse for a "0", and a 2 mSec pulse for a "1", as these values can be easily generated by a BS2 and detected by a second BS2 (using FREQOUT and PULSIN).
thanks again,
justin
·· You could use the Phototransistor you have, if you build the Demodulator circuitry yourself.· Before the 3-pin IR Demodulator device was available, Radio Shack sold the 555 and the 567 ICs...The 555 Timer was used to modulate the IR beam, and the 567 was used to decode it (Through an op-amp, 741, also available at Rad Shack).· I believe these schematics are still available through the Mini-Engineer's notebooks Radio Shack used to carry (They still should).
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Chris Savage
Knight Designs
324 West Main Street
P.O. Box 97
Montour Falls, NY 14865
(607) 535-6777
Business Page:·· http://www.knightdesigns.com
Personal Page:··· http://www.lightlink.com/dream/chris
Designs Page:··· http://www.lightlink.com/dream/designs
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1: Out
2: Gnd
3: Vcc
I just need some guidance on how to hook this thing up to the basic stamp, if anyone knows
thanks
edit:: ok, scratch that, its simpler than I thought [noparse];)[/noparse]
thanks again for everyones help
Post Edited (Whelzorn) : 10/14/2004 1:21:26 AM GMT