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Dubai, UAE
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Hi,
   Can anyone confirm for me that the different frequencies of IR Detectors available have their band pass filters tight enough that I could point a 40Khz transmitter directly at a 38Khz receiver at close range without it detecting the signal ?

Its a neat solution to running multiple cars on my laptimer boxes if its possible.

All of the boxes are 38Khz at the moment so single car only unless I build a multi car protocol in software, I would much rather just use a 50 cent component if its possible.



Thanks

Duane B

rcarduino.blogspot.com
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SF Bay Area (USA)
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No; pick them further apart if you can (33kHz and 40kHz, for example.)
(This is from the datasheet, which typically show 40% sensitivity at 10% off-center frequency, in a nice bandpass-filter-shaped graph somewhere.  I haven't actually tried it, though I was considering a similar application at various times.)
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Dubai, UAE
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Hi,

   Thats disappointing. I will order some from either end of the available range as you suggest and see how I get on, I really don't want to have to do this in software if I can get a piece of  50 cent hardware to do it.

Thanks

Duane B

rcarduino.blogspot.com
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the land of sun+snow
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westfw is 100% correct about the rolloff characteristics. Look in the datasheets.

A while back, I built my own IR proximity detectors that had adjustable detection
ranges, going from about 18" down to 6". I simply varied the driving frequency on
the IR Led from about 32-38 khz, and took advantage of the rolloff in sensitivity.
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Dubai, UAE
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Thats a really neat idea, I had seen an approach where the emitter is driven through different resistors to sense reflection at different ranges, but your approach gets away from the need for additional components.

Unfortunatley for me though, it looks like I am stuck with implementing a software solution or maybe building some very tight filters with opamps might be an option ?

Duane B
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Couldn't you superimpose different coded data stream loops onto each of the 38kHz signals and interpret from the data stream which car is sensed.
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Dubai, UAE
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Yes, but If I could have done it in hardware for 30 cents I would have preferred to, here is a candidate solution -

http://rcarduino.blogspot.com/2012/08/lap-timer-potential-coded-transponder.html

Other than that I can get at least two cars running using 555 Timers, one with a long pulse and the other with rapid short pulses, it should be trivial to tell the two apart in software.

Duane B

rcarduino.blogspot.com
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the land of sun+snow
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IR detectors come in different frequency ranges, eg 32, 38, something else, and
56-Khz ranges as I recall. You might be able to get adequate isolation by using
one 32 and one 56 Khz device.
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Dubai, UAE
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That sounds like a viable option, I will have a look what I can order in the UAE,

Thanks

Duane B
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