RF 434Mhz Multiple transmitter and single receiver

[itznaidu]

Hi,
I am working on 434Mhz RF modules along with HT12E and HT12D. I have two transmitter and one receiver.
The two transmitters A and B have different address on them but work on the same frequency
When the receiver address is set to transmitter A, it receives proper data from transmitter A provided transmitter B is off.
When the receiver address is set to transmitter B, it receives proper data from transmitter B provided transmitter A is off.
But when both the transmitters are on, The receiver VT pin (on HT12D) is always zero. But any of the one is on and proper address is set. it works.
but not when both the transmitters are on, even though they have different address.


Please help me on this.
My project involves a total of 9 transmitters.
If I am stuck at two then I cannot go till 9.

 

[FvM]

The solution is simple and straightforward. Don't enable the transmitters permanently.

 

[itznaidu]

But unfortunately, In my case all the transmitters will be on.
Any solution for this will be really appreciated.


My doubt is, what is the point in having address switches on HT1E and HT12D

 

[FvM]

This is a basic problem of wireless communication. You can't have two or more transmitters of same carrier frequency sending simultaneously. At best the strongest signal will win, with AM modulation most likely you get no transmission at all.

But unfortunately, In my case all the transmitters will be on.

If so, you need to reconsider the project concept.

 

[itznaidu]

could you help out with the project concept.
The project is there will be a transmitter on each person. and the receiver will be with the manager. whenever a person comes in to the office, the respective led will glow. if he goes out, the respective led will be off.

PS: yes, RFID is an option. but I want to get this done using only RF 433Mhz.

The chances of getting this done is only based on your suggestion.
I would really appreciate ur suggestion

 

[FvM]

In this case, I don't understand how you came to the conclusion, that the transmitter must be continuously on. Sounds like a lack of common sense.

They need to transmit periodically with reasonable intervals. That's how most multi transmitter systems work.

 

[firevsice55]

If possible use another RF module, I am currently using RFM12 which are available in India. They are also easy to configure.
Use can as many transmitter and receiver pairs.
9 tx and 1 rx very much possible, no problems at all.

 

[tony_lth]

Use CW detection technology, like that in the telecomm. Every time, when a transmitter want to transmit, first it need to listen the CW, if there are some CW, delay the transmit randomly.
Or use the ACK technology, every time when transmit, wait the reply from the receiver. If not receive the reply, delay randomly and send again.

 

[FvM]

Use CW detection technology, like that in the telecomm. Every time, when a transmitter want to transmit, first it need to listen the CW, if there are some CW, delay the transmit randomly.
Or use the ACK technology, every time when transmit, wait the reply from the receiver. If not receive the reply, delay randomly and send again.

Basically a good method, but unsuitable for a simple system with transmitters only and no built-in intelligency.

Sending short packets with low duty cycle and random timing should be completely sufficient for the present problem.

Once itznaidu starts to think about battery lifetime and other "real world" problems, he'll get the idea on his own.

 

[Laxman Kumar]

did u able to transmit data with both RF modules...
i am also getting same problem.....how did u fix it????

 

[FvM]

did u able to transmit data with both RF modules...
i am also getting same problem.....how did u fix it????

Reading the previous discussion should help you. Therein the underlying problem is analyzed in detail and several suggestions are made.

 

[itznaidu]

did u able to transmit data with both RF modules...
i am also getting same problem.....how did u fix it????

You cannot solve that problem, since both work on the same frequency, frequency jamming cannot be avoided.

You need to write a program that the transmitters are alternatively on

 

[Laxman Kumar]

You cannot solve that problem, since both work on the same frequency, frequency jamming cannot be avoided.

You need to write a program that the transmitters are alternatively on

And what if i use One rf transmitter of 433 mhz and other of 315 mhz then...will it work????

 

[itznaidu]

And what if i use One rf transmitter of 433 mhz and other of 315 mhz then...will it work????

yes it will work fine.