IR tx rx synchronisation

[ragul07]

how to synchronize the infrared tx and rx in an array so that interference between each pair of the Tx and Rx are avoided??
Or Is there any method to use IR tx and rx without interference..?
this project is similiar to IR curtain
need ur help fellas
thanx in advnce

 

[123jack]

If I understand correctly you are trying to use multiple IR transmitters in close proximity at the same time?

This can be quite tricky and I've never done it but things that occur to me are:

First minimise external sources as far as possible -eg. sunlight, flourescent lighting etc.
Look to modulating your IR at different frequencies
Of course use different codes for each reciever to be sure to prevent the wrong device responding
If possible you might be able to get all your transmitters to talk to each other and have them transmit
within sequenced time windows (TDM for infra red no less)
I'm not sure what else you could do but you should be able to work with that - For the record I have IR headphones
and also use an IR remote pointing near the audio transmitter with no problems so it can be done with little interference.

 

[ragul07]

thanx for the reply 123jack
i tried modulating along with encoding and decoding...along with diff frequencies..
i used two ir TX n RX but what happens is higher frequency signal is recieved correctly but the lower frequency signal in interfered by the higher freq signal leading to improper reception..

 

[123jack]

hello ragul

How are you defining "improper reception?"
Do you mean the signal is corrupt as seen perhaps on a scope - or do you just mean
the reciever isnt doing what you expect?
What frequencies are you using and how are you modulating the signal and
what addressing protocol are you using?
Perhaps if you can upload a circuit and code we can help easier.
More info would help a diagnosis.

 

[KerimF]

I doubt you can get, for sure, the practical answer you are looking for (even if someone know it) since your question is about a general case.
In other words, every useful answer here will be based on some assumed factors that may or may not reflect the ones of your application.

 

[ragul07]

I used the HT12E n HT12d encoder n decoder respectively.
I used the 555 timer to modulate the signals
wat i meant by "improper reception" was that the data bits which were set in the TX part was nt recieved properly..!
I didn interface it with a micro controller..i would interface in the later part of the project.

- - - Updated - - -

HI KerimF
my application is just similiar to the Light curtains.. used for safety n security...

 

[KerimF]

Could the following protocol be applied for your application?

The transmitter unit contains light emitting diodes (LEDs) which emit pulses of invisible infrared light when energized by the light curtain’s timing and logic circuitry. The light pulses are both sequenced – one LED is energized after another – and modulated - pulsed at a specific frequency.

 

[123jack]

Hi ragul
Are you sure anything is getting transmitted? If so how?
do you have a scope available?
If you dont you could point a digital camera at the IR LED and at least see a flash.
A scope capture of tx and rx signals would help
as would circuits. We dont really have anything to go on except guessing.

 

[ragul07]

Hi KerimF...!
Your assumption is correct..!
I had implemented 70% of the work...
That project is kept aside so i didn get into forum for a long time..!

Thank you for the reponse