Go Down

Topic: Quick IR Question (Read 579 times) previous topic - next topic

DuaneB

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.

http://www.youtube.com/watch?v=ryQFShhtzlQ

Thanks

Duane B

rcarduino.blogspot.com

westfw

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.)

DuaneB

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

oric_dan

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.

DuaneB

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

Go Up