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RF tranceiver problem

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darvaish

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Iam using RF transmitter TXM-418-LR and RF receiver RXM-418-LR from LINX TECHNOLOGIES both modules are connected with the mcu PIC18F452
Modules have seperate antennas.I am using them as half duplex tranceiver
transmitters datain pin is connected to TX of USART and recivers dataout pin is cnnnected to the RX of USART in mcu.supply votage of both modules is also controlled by mcu such that at a given time only one of them is working


I have tested the RF modules seperately.I gave a square wave at the input of the transmiiters datain pin and then checked the output on receivers dataout pin by an oscilloscope.Igot the same signal back which means that my RFmodules are working fine.

Now i connected the transmitter to mcu#! and reciver to mcu#2.
mcu#1 is transmitting a counter serially and mcu#2 is supposed to receive that counter.


Now the problem is that i am getting data in mcu#2 but its not correct some values are correct some are false.

can anybody tell me what is the problem when my transmitter and reciever and also microcontrollers are working fine individually the what is the problem when they are integrated

I think that the problem is in the synchroni9zation aof serial data when it is transmitted wirelessly

aNY SOLUTION TO THIS PROBLEM
 
You can't send standard serial data via most RF modules, you need to use some kind of coding scheme - Manchester coding is the type most commonly used for this.

Basically the reason is that the modules are AC coupled, so you can't send a continuous HIGH through them - standard RS232 uses a continuous HIGH between bytes, this prevents it working.

If you invert the serial data (has to be in software, the hardware UART can't do it!) you can get the modules to work - BUT, it's a fairly crude solution - you should use Manchester coding, or some similar NRZ system.
 
I had an identical problem with a very similar 433MHz TX/RX pair. Seperate antennas, good range for 9.6KHz square waves; bad performance with data or constant values and so on...

I changed my software to send Manchester frames that were similar to the "RC5" encoding for infrared TV remotes and got improved results. Occaisionally though, the receiver would start reporting random data, and for lack of a better explaination, I chalked it up to urban radio chatter. I'm ordering a second receiver to confirm this.

Also, if you're concerned about synchronization (and who isn't), you can send two Manchester start bits to synch the receiver and maybe do some baud-rate detection for good measure. I had my radio pair re-synch after every 14 bits (another RC5 property).


Anyway, keep us posted on this, darviash. I am very interested in these UHF projects.
 
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