RF 433 MHz Multiple Transmitter and Single Receiver

[rajesh279]

Hi All,

I have been asked to work on a new project. It is like this:

RF433 MHz Transmitter - 3 Nos.
RF433 MHz Receiver - 1 No.

Any transmiter can send data to the receiver and receiver has to to
read it. Request can from any transmitter, the receiver has to
sequentially receive the data and display it on LCD/LEDs.

I am aware of single transmitter + single receiver, but not mutiple transmitter.
Can anyone suggest me how to design for multiple transmitter ?

Regards,
Raj s.

 

[prabhukaran3]

Hi Rajesh,
Any transmitter can speak with the receiver if all are having same device IDs(Address bits). Problem is how frequently it will speak.? There is a chance to collision between all messages.. So we have to much care about transmission rate...

What is your project actually? Getting data and just displaying it seems meaningless because there is no chance to identify the sender. If its not necessary means you go ahead..Sure it will work

 

[hobbyckts]

It depends on the encoding on the transmitting side and decoding at the receiving side.

 

[bigdogguru]

Any transmiter can send data to the receiver and receiver has to to
read it. Request can from any transmitter, the receiver has to
sequentially receive the data and display it on LCD/LEDs.

I am aware of single transmitter + single receiver, but not mutiple transmitter.
Can anyone suggest me how to design for multiple transmitter ?

Unfortunately, the inherent limitations of a simplex communication scheme, such as the ASK TX/RX pairs to which you refer, preclude any sense of "reliable" communications from being implemented.

The receiver module lacks the ability to acknowledge a successful transmission of a packet or request a resend of a corrupted packet due to EMI or a collision.

The transmitter module lacks the ability to receive an acknowledgement of a successful transmission of a packet or a resend request to retransmit a corrupted packet due to EMI or collision.

In short the transmitter module has no means to determine if a packet was successful received and the receiver module has no means to determine is a packet was ever sent. It should mentioned, there is also no reliable means for the transmitter and receiver modules to synchronize themselves and implement an effective multiplexed communication scheme.

Utilizing multiple transceivers will only increase the probability of collisions and exacerbate the situation as a whole.

It would be far more prudent to invest in a few inexpensive transceiver pairs, like the nRF24L01+, which are available on eBay for under $2 USD a pair and support implementation of multipoint communication schemes.

BigDog

 

[rajesh279]

My prototype project is like this:

There are 3 Transmission devices having keypad which user will press and send numbers. Say,
Device 1 sends: 101
Device 2 sends: 102
Device 3 sends: 103

Each device will send unique number and this is fixed as shown above.
User can press any device at any time.

Now the receiver should receive all the Transmitted data and display one by one. The LED display handling is not problem.
But the issue is, how to set up the communication between Transmitter and Receiver so that Receiver can handle all the data without losing them?
Any Encoder Decoder like HT12E/HT12D is required or not?
Or any packet format of data like [HEADER + ADDRESS + DATA + CRC] shall work?

Regards,
Raj S.

 

[chuckey]

As explained it is a problem because at one time you could have three signals received and the receiver must be able to sort them out. The easiest way I think is to use very different modulation frequencies for each transmitter and use a sinewave type modulation. So the output of the receiver then can be filtered and three different modulation frequencies recovered. It is best if the modulation frequencies are not harmonically related, say 1100, 1700 and 2400 HZ.
The other thing to remember is that a very strong signal from the nearest transmitter will reduce the gain of the receiver, so a weak transmission might not be decoded. I would think that the carriers should be switched off at a low frequency rate so when the strong one is switched off the weak one can be heard.
Frank