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Choosing IR receivers

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edeca

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I am attempting to build a small IR blaster, for use outside. The idea is there will be one receiver and multiple transmitters, each sending a different ID.

The transmitters will constantly transmit with a repeat of something very short like 45ms. They will be moving, thus only detected as they pass the receiver.

The receiver will be mounted in a tube to reduce glare from the sun and to aid directional detection. I plan on using a simple protocol like the Sony IR one, which I have already implemented.

I am trying to mock this up on breadboard so I can see what speeds realistically the transmitter may pass the receiver at in order for reliable detection. Distance for transmission is actually quite short, probably maximum 2 metres.

My question concerns the receiving method. Basically my choice seems to boil down to:

  1. IR photodiodes
  2. IR phototransistors
  3. TSOP IR receivers

I bought a bunch of photodiodes thinking they would be the best solution, but obviously they don't have a logic level output. When they detect, a very small current will flow. They are fast, but would require coupling with a transistor.

Advantages of the phototransistors seem to be logic level output (straight to my uC) and no need for a carrier, e.g. 40Khz.

Advantages of the TSOP receivers seem to be the in-built filtering and amplification. In addition, a 1/4 or 1/3 duty cycle signal on top of a 40Khz carrier would actually reduce power requirements. This makes the transmitter software marginally more complex.

So does anybody have any recommendations what to choose? I have never used any of the three, so would welcome ideas on which might work best.
 
go with plan C, the carrier and amp filter noise, making it more accurate, and increases the range , so I hear

the transmitter then just needs something like an "and" gate with a 40khz square wave
 
This topic has been covered many times on these forums. Go with the IR receiver. Nigel has good about encoding for IR remotes on his web page.
 
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This topic has been covered many times on these forums. Go with the IR receiver. Nigel has good about encoding for IR remotes on his web page.

Indeed, it has been covered for transmitting data inside. I've got a pretty specific application and I was wondering about recommendations. I will write it up fully once I have got it working.

Thanks for the two confirmations so far.

And to be fair, there are more recent tutorials than Nigel's. This PDF has a great flowchart if you want to implement it yourself. This page has some good graphs of expected transmissions. And lastly, this one covers the modulation. That is all Sony specific of course.
 
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The TSOP's are by far the best for your outdoor application as they already have some ambient light immunity built in, good range and sensitivity. Your plan has no conflict management. Can two transmitters "hit" the receiver at the same time?
 
The TSOP's are by far the best for your outdoor application as they already have some ambient light immunity built in, good range and sensitivity.

Perfect, thanks. That's what I didn't know about. In that case, I am assuming the IR photodiodes and transistors are only good for beam break detectors and similar applications.

Your plan has no conflict management. Can two transmitters "hit" the receiver at the same time?

That is actually physically impossible, fortunately. Even if it could happen, using a state machine based approach to the decoding should remove any errors that would happen due to a badly transmitted message. It will also remove the problem of what happens if you only catch half a message, i.e. the start or end, as the object is moving.
 
I think you are good to go then. Put it in the tube to shield against direct sunlight. You can get there with photo transistors, it's just that the TV sensors have done all the work for you. Google for the data sheet. It's an amazing little part.
 
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