enter image description hereI am undergraduate electrical engineering student. I have a project for Analog Electronics course. I should design a system which tries to equate the heat of two stations with a controlled cooler with wirelessly received heat information. The system basicly will look like as the picture in attachments. The confising point is that I am supposed to implement two transmitters one receiver wireless communication module. And the minimum distance should be at least 1 meter. What do you think to best way for wireless communication for this project. There may be lots of choses lik using two speaker and a microphone or using two laser and an LDR. I tried to use two laser (with changable duty cycle respect to changing temperature). I can transmit that square wave to my receiver (LDR). But I could not find a solution transmitting two information to a single receiver. Any idea?

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  • \$\begingroup\$ Sorry for that, it was my first post. I've just edited \$\endgroup\$ Dec 19, 2016 at 16:35
  • \$\begingroup\$ Is there a reason why you can only have one receiver? Can you just have separate receivers? What is the controller? \$\endgroup\$ Dec 19, 2016 at 16:40
  • \$\begingroup\$ Using a single receiver is indicated in he project definition. So it is forbidden to use more than one receiver. Controller basically should do that, if the second station's is hotter than first station the cooler should start to work and cool the second station. The main aim is equalize the heats of the stations. \$\endgroup\$ Dec 19, 2016 at 16:58

1 Answer 1


There's lots of different ways multiple transmitters can share a receiver or a medium.

Classically, we organize these in four categories:

  • Time-based multiple access (the different transmitters simply don't transmit at the same time)
  • Frequency-based multiple access (information is coded onto oscillations of different frequency, which don't interfere with each other)
  • Spatial multiplexing (the receiver is able to tell signals coming from different directions apart)
  • Code multiplexing (You find sets of functions which are orthogonal under some dot product, and each of your transmitters uses a different one. The superposition of multiple signals can be losslessly deconstructed into the original data by applying that dot product)

All these methods work with any signal – they're most prominently used in digital radio communication, but there's no reason why Code Division would not work for e.g. infrared comms. In fact, I think there's multiple IR data communication standards that do that. And, for example, infrared remote controls avoid interference with normal sources of light (like lightbulbs) and other infrared-based comm systems by employing basically frequency division principles.

I'd drop the laser idea – a laser typically generates a focussed beam, and you don't need that – a simple LED that illuminates a larger region is much easier to handle.

  • \$\begingroup\$ But especially at ranges of 1 meter, it will be extremely difficult for a newbie to detect such a low level signal from an LED.. \$\endgroup\$ Dec 19, 2016 at 17:04
  • \$\begingroup\$ @WhatRoughBeast aside from that newbie absolutely having the chance to simply use eg. existing infrared remote ICs? Also, no, it's really not that hard for an EE undergrad to come up with a digital or analog filter that would be able to allow for frequency multiplex. The CDMA approach would in fact not be much harder. \$\endgroup\$ Dec 19, 2016 at 17:07
  • \$\begingroup\$ (of course, assuming the EE undergrad student already had some minimal lecture on signals and systems – but from the project description, it would seem that way) \$\endgroup\$ Dec 19, 2016 at 17:08

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