Hi
My project is a telemetry system which need two RF transmitters and two RF receivers

I have a car which carry three sensors and I need to send the data from the car to the base board to view the data on lcd display
In the same time I need to control the car from the base board
Every thing is OK but I do not know how to deal with the RF modules

How to make one receiver to be effected form one transmitter?

Any one could help me doing that?

This is a picture for my car before several modifications

There are two simple options:

1) Use radios on different bands, usually there are two licence free bands spaced well apart.

2) Use simplex transmission - where only one side transmits at a time, so send data to the car, then turn off the transmitter and wait for a reply from the car. This does result in a fairly slow control system though. It could be speeded up somewhat is there isn't any need for continuous feedback, with the car only sending data when instructed to by the remote.

Thank you Nigel

it seems that I'm going to use the second option, because only one kind of RF modules are available here.
another question about the modules

the devices I had have the flowing specifications
frequency 434 Mh
Am Modulation (Amplitude Shift Keying)

While the transmitter is not powered up or its input is free or connected to ground
Random signal is illustrated on the oscilloscope.
Only when the input is connected to VCC, low level signal illustrated at the output

Is this normal behavior of my modules?
And how to make the PIC understand the random signal as silence situation?
Is it possible to rectify it?

Check my PIC tutorial - Manchester coding is what you need!.

would using 2 different frequency modules be perfect?

TLP434A - 433.92MHz
TLP418A - 418MHz

http://www.futurlec.com.au/RadioModules.jsp

say your working with 2400 baud, if you made the controller the master and by doing so, it controlled the data flow i.e.

codes:

"C", 10,Speed - Tell car to go back with the value of speed
"C", 20,Speed - Tell car to go forward with the value of speed
"C", 30,Angle - Tell car to turn left by the amount of angle
"C", 40,Angle - Tell car to turn right by the amount of angle

"S1", 10 - command sensor 1 to send its data now
"S2", 11 - command sensor 1 to send its data now
"S3", 12 - command sensor 1 to send its data now

Make a small program that records how many ms it takes to sample and send the sensor data, and make that time the time_out for the wait on the reply on the master (controller)

say it took 1ms to sample and another 20ms to send the data from the sensor, then from the controller:

Time_Out: 'If it took more than 25ms, come straight to here

SEROUT PORTA.0, 396, ["S1", 10, "A"] 'Tell sensor 1 to send data

SERIN PORTA.0 , 396, 21, Time_Out, [ WAIT( "S1" ), SERDATA]

'Do what you want with the SERDATA



and on the reciever

Time_Out:

SERIN PORTA.0 , 396, 20, Time_Out, [ WAIT( "S1" ), SERDATA] 'wait for controller to request a new value

SERDATA = ADIN 4

SEROUT PORTA.0, 396, ["S1", SERDATA, "A"] 'send the new sensor value

SERDATA = 0 'reset the data

Goto Time_Out ' go and wait for the next request



Car Program;

Time_Out:

SERIN PORTA.0 , 396, 20, Time_Out, [ WAIT( "C" ), SERDATA, Speed] 'wait for new data

If SERDATA = 10 then
'make it go as fast as the value Speed
Elseif SERDATA = 20 then
'backwards
Elseif SERDATA = 30
'left by speed value
Elseit SERDATA = 40
'right by speed value
Endif

Goto Time_Out


Controller;

'decode user inputs and determine serdata and speed values

SEROUT PORTA.0, 396, ["C", SERDATA, Speed, "A"] 'send the new car data



Its all mumbo jumbo i know, but work with me here