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[PIC] 433Mhz RF transmission problems

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K33rg4t3

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Hey
I want to make a simple 433Mhz transmission.
I am using cheap Rf modules from aliexpress.
I have connected the sender module to TX pin of first PIC, and receiver module to RX pin of second PIC.
I have set up a 1200 baud rate UART connection like that:
Code: 
    UART1_Init(1200);

And I transfer data like that:
Code: 
       UART1_Write_Text("Hello Radio!\n");

The problem is that only 1 / 3 packets are correctly receiver, most of the time I am getting garbage.
When I connect the serial TX with RX by wire and add common GND connection, everything is transferred correctly.

What should I do to improve the radio communication? I only need to send around 10 bytes per second, no more.

Both PICs are using 12MHz crystal.

Any ideas or suggestions?


EDIT: I have tested even baud rate 300 now, and here is the received data:
Code: 
˙Hello radio!                                  
Z6Ű&#K{¦                                          
Hello radio!                      
Z6Ű&#K{¦                                                
Z6Ű&#K{¦                                             
Z6Ű&#K{¦                                               
Hello radio!                                              
Z6Ű&#K{¦                                              
Z6Ű&#K{¦                                               
Z6Ű&#K{¦                                               
Z6Ű&#K{¦                                              
€+cc{&#K{¦                                         
Hello radio!                                            
Hello radio!                                            
Hello radio!                                             
Hello radio!

as you see, the string is received incorrectly very often ...
 
Last edited:

It's good result! At least you are receiving some data. It is not wired communucation. A lot of noise and errors will always present. Use modules with h/w crc checking like NRF24L01 for exapmle.
 

cheap ASK modules won't give you good result unless you code them properly. Manchester coding or other suitable coding schemes. I strongly recommend you to use HT12E/HT12D encoder decoder pair ICs for acceptable result. Otherwise, you better use nRF24L01+ or similar standard modules as Easyrider83 suggested.
 

I have improved the signal quality by using
- preamble (three bytes)
- manhattan coding (without it transmitting three null bytes or more is messing up the signal)
And it is working better now.
 

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