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Author Topic: Infrared Barrier  (Read 1630 times)
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quark576
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« on: November 15, 2007, 01:27:51 01:27 »

I experiment a IR barrier with two pic ,one for Tx (driver with 16f648 Pwm 30 Khz) switch On/Off the carrier , another with sfh505 IR receiver all is OK I reach indoor about 5 meters but in external don't work
I test with a TV remote and seem work fine, may be I want a more power ?

any idea ?  Thanks
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FaithNoMore
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« Reply #1 on: November 15, 2007, 03:03:42 03:03 »

Use IR Laser LED and add lenses on both TX and RX if you have them.
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FriskyFerret
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Put it in, take it out.


WWW
« Reply #2 on: November 15, 2007, 03:43:21 03:43 »

How hard are you driving the IR emitter? Because its a pulsed application you can usually exceed the manufacturer's maximum current rating as long as you keep the average power with specification limits.
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Dancing pants and leotards, that's what I'm talkin' about!
bogdantk
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« Reply #3 on: November 15, 2007, 07:49:03 07:49 »

Hello
The receiver has an automatic gain control. When exposed to sunlight the
receiver front end is saturated and the gain is minimal so the barrier active
zone is very short. To avoid this try to put the receiver in a shade avoiding
direct or reflected sun light, also a very useful solution is a tube with 20-40
mm diameter and 30-40 mm long coaxial with the receiver active area (a small
lens).
All the best
Bogdan
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freddy
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« Reply #4 on: November 15, 2007, 11:13:15 11:13 »

Yes quark576 i confirm the bogdantk opinion.
With sunlight the AGC is in saturated mode.
I've try some yrs ago with TSOP1730(30KHz) TSOP1738(38KHz) of Vishay
an outdoor application and i've do 6 meter with no problem.
I think thats' AGC of TSOP working better of AGC of SFH505.
Try with TSOP but a little tube is ever the optimal solution.

Bye
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quark576
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« Reply #5 on: November 15, 2007, 09:18:44 21:18 »

Ok , I will test next week end .I have also Tsop 1138 to try.
I will inform a forum with my tests.

Thanks for All
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tae
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« Reply #6 on: December 01, 2007, 02:56:35 02:56 »

As freddy said , use modulated signal and decouple DC from the photodiode. Diode should be biased such as it should not saturate from neither excessive radiation nor from dark current dependent on temperature (btw the first part is much more) .
Things can do better if at reception side you will add bandpass filter , and if more distance is needed - put more diodes in parallel .
Laser is good choice but its ray should be aligned to photo receiver .
6 meters is not a problem for IR.

Please pay attention to sensitivity and threshold of receiver .  IR can easily be reflected from walls or any other objects so cross detection wont work .

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abc
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« Reply #7 on: January 16, 2008, 11:11:40 11:11 »

hello quark576,
u can use tsop1738 also
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localcrack
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« Reply #8 on: January 16, 2008, 09:15:26 21:15 »

you may use coding style like HLHHLH or any other and decode with pic for accurate result. you may define bit time in software and chek that bit time at other end in decoding. in this way you remover false triggering.
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