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How large is an IR diode radiation spot area?

I put some IR diodes (receiver and transmitter) in front of each other. I want each transmitter IR diode to only radiate on its reciever and not effect other receivers. I need to know how much space should be exist between receiver diodes.

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  • \$\begingroup\$ How long is a piece of sting: Not all devices are the same. How big is a thing? \$\endgroup\$ – Andy aka Feb 24 '20 at 9:42
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    \$\begingroup\$ Why would you want this? Does it need to be wireless or is it just for the galvanic isolation? In that case you could use optocouplers instead! \$\endgroup\$ – LukeHappyValley Feb 24 '20 at 15:26
  • \$\begingroup\$ @Andy aka sorry I dont get your point. \$\endgroup\$ – sepehr Feb 24 '20 at 19:38
  • \$\begingroup\$ @LukeHappyValley yes it needs to be wire less. I want to detect something like an obstacle or sediment in water. \$\endgroup\$ – sepehr Feb 24 '20 at 19:40
  • \$\begingroup\$ There is no generic spot area; it varies from device to device and you haven’t said what device it is. \$\endgroup\$ – Andy aka Feb 24 '20 at 19:45
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The simplistic approach that you show will not work for almost any distance between the devices. You will need to apply some more technology to have any chance of getting anything to work similar to what you envision.

For close proximity where you align the transmitter physically close to the receiver you may be able to get this to work by adding an isolating tunnel around and in front of each receiver IR diode. This would effectively let each receiver just see what is directly in front of it in a narrow spot.

If you envision something that you want to use over an appreciable distance then you are going to have to resort to a special modulation protocol that allocates a certain part of the protocol to each of your channels. This can take many forms depending upon how much effort you want to invest in the design. One approach would be to devise a transmit protocol divided up into N time slots with a distinguishing frame syncing to identify when the channel slot sequence starts. A decoder circuit or MCU behind each receiver looks for its specific time slot to strip its specific data out. In this scheme you could drive all your transmitter IR LEDs in parallel (or just use one).

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  • \$\begingroup\$ thanks. I have to describe that I need to detec water sand or big sediment something like small rocks under water and I cant use isolated tunnel. But about your second advise, could you explain in more detail please? \$\endgroup\$ – sepehr Feb 24 '20 at 19:49

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