PIC-PIC RF Comms

[Kamikaze47]

Ive set up 2 16F84A's to talk to eachother via RF using a 433Mhz Trans/Recv pair running at 4800 baud.

My code is below, but something must be wrong becuase the range is a mere 1m. Any further than 1m and it just doesnt work.

Anyone have any ideas on what could be wrong?

These are the data sheets of my RF units:
http://www.altronics.com.au/download...eets/Z6905.pdf
http://www.altronics.com.au/download...eets/Z6900.pdf

Transmitter Code:

low PORTB.1                                 ' Initialise RB1

start:
Serout2 PORTB.1,16572,[$55,$55,$66,$95]     ' Transmit "$95"
Pause 500                                   ' Wait
Serout2 PORTB.1,16572,[$55,$55,$66,$99]     ' Transmit "$99"
Pause 500                                   ' Wait
Goto start                                  ' Repeat
End

Reciever Code:

recvd var word                              ' variable decrarations
recvd=0                                     ' clear recvd
low PORTB.0                                 ' turn off LED
input PORTB.1                               ' set RB1 to input

start:
Serin2 PORTB.1,16572,[wait ($66),recvd]     ' wait for $66, then store data
if recvd=$95 then High PORTB.0              ' if recvd=1 turn on LED
if recvd=$99 then Low PORTB.0               ' if recvd=2 turn off LED
goto start                                  ' loop

end

[languer]

Can you qualify more the statement "it just doesnt work"?

Does it not receive anything? garbage?

The way you have it setup it will sit on "Serin2 PORTB.1,16572,[wait ($66),recvd]" until it receives $66. So you may want to have a timeout, and even here noise will probably cause the same problem (i.e. timeout will never occur).

A quick look at the receiver module says it supports 4800bps and 3kpbs as maximum data rates (this in itself is contradictory). Even if it did support 4800bps for maximum rate you probably do not want to excercise this. Try 1200bps to begin with.

This are just some ideas to get you going. There are many threads on RF comms here, search them as they have very useful information.

[Kamikaze47]

Im not sure what its recieving once it gets past 1m. I dont have an LCD handy to send the recieved data to (I will pick one up tomorrow). Once its more than 1m away, the LED stops flashing, indicating that its not recieving the data that i am sending it.

I'll try reducing the baud to 1200 and see what happens.

[Kamikaze47]

Reducing the baud to 1200 improved the range a fair bit. At 5v I now get about 15m line of sight. At 12v, about 30m... Still a fair way short of the 100m these units are supposed to achieve, but not too bad.

[Ron Marcus]

Just for giggles, try increasing the number of $55s you send to..say 8. Next pick a more balanced header character like $AA. You can also put a small character delay using DEFINE (Maybe 1 mS). If this helps, you need more of a preamble to balance the data slicer.
What are you using for antennas? Usually the companies range test their units with twelve element Yagis. Well, maybe not that bad, but the test data is usually taken in an optimum noise free environment with no multipath. These parameters don't exist on our earth, and you should probably halve most manufacturers range estimates. I've had to test most offerings in the OOK market, and upgraded to FSK for my more serious work, and better impulse noise immunity.

Ron

[Kamikaze47]

For antennas Ive tried using 1/2 Wavelength and 1/4 Wavelengh bits of coathanger wire, and found the 1/4 Wavelengh (6.47 inches) to give better range.

The reason I used $66 as a start character is becuase it is fairly balaced (same number of 1's and 0's). I will try $AA though, and will also try adding more $55s and see if it improves the situation.

Thanks for the advice guys.