Wireless microcontroller device help required!!!

I am trying a wireless microprocessor based road safety device.
My device consists of two parts. An FM (I am using a walkie talkie for this) transmitter and an FM reciever.The FM The transmitter

is attached to a signboard/traffic signal/direction board .The reciever is inside the vehicle.






Transmitter

This is a wireless transmitter which uses FM frequency(I am using a walkie talkie for this) to transmit wireless signals to the reciever inside the

vehicle as soon as the vehicle comes in range with the transmitter on sign board say 1 meter .It consists of ATMega 8515

Microprocessor which which I want to code to send a particular binary code (....or some other type of code ....Please help me in this part)(which depends on what the sign board

is Eg.If the sign board means slippery road ahead.and the code of this message is "1",it will transmit "1" in

the form of binary signal to the reciever device.







Reciever

The FM reciever (I am using a walkie talkie for this) will pickup the binary code and transfer it to the microprocessor(ATmega 8515) which will convert it

into digital signal and find the message that matches the code "1"(i.e. slippery road ahead)in the flash

storage device(memory " ATMEL608 24C512 . PI18 A ")where many messages are stored in the local language of the driver .finally the message

will be transfered to the speaker of the vehicle . thus the vehicle driver will come to know that the road is

slippery and he/she will slow down .


LIST OF COMPONENTS THAT I HAVE QUANTITY
ATMEGA 8515 16PU 0621 2

ATMEL608 24C512 . PI18 A 1

pROGRAMMER FOR ATMEGA 8515 + PROGRAMMING SOFTWARE



UNFORTUNATELY ,I do not know how to make the circuit for the above device . can someone help me with the circuit of the transmitter and reciever parts .

You prefer to use an FM walkie talkie for the transmitter and receiver, so it would be helpful to know which model of walkie talkie you prefer to use. Since we must interface to these walkie talkies, a bit more information can be had by looking up the specs for the chosen model.

When interfacing to an FM voice radio, you can choose to do so through the microphone and speaker connections, which would be the easiest, or you can choose a more complex method. If you choose to use the mic and speaker connections, say, through a headset connector on the walkie talkie, then you must learn that these connections are AC coupled and filtered to pass primarily 300Hz to 3000 Hz only. The pass band is also not particularly flat in many cases. So, if you must pass some sort of serial bitstream through this, you must run it slow enough to pass through this bandwidth, and you must ensure that there is no spectral energy below 300 Hz.

One way to avoid these complexities is to modulate your data into some sort of audio. One common and old fashioned but reliable way to do this is using DTMF tones. The idea is that the transmitter sends a pair of tones to represent a logical one and a different pair (or no tones at all) to represent a logical zero. But you are then limited to passing fairly slow data since the tone decoder must hear quite a few mSec of tone to decode them, so only tens of bps is practical. In any case, DTMF transmit and receive chips are available still.

If you have not already procured the walkie talkies, then consider a more up to date method. For example, you might consider using a zigbee transceiver pair available from Digi International (through several distributors). One model worth looking at is the XBeePro available as small pcb modules with serial port interface for approximately $20 each. These would be relatively easy to interface to the serial port of your uP. The range, however, might be disappointing since they only work over perhaps a range of 25 feet or so.

Thanks for your help
I would like to tell you that want to do it through the microphone and speaker connection and this is only a prototype I am building. I just want 3 different messages to be stored in the memory chip . Though I am not sure but I feel that three binary codes can be sent easily even if the data transmission is slow .

The walkie talkie I am using is a fairly simple one and can send morse codes . I dont exactly know the model as it is a pretty old one and may have costed only $5 or something.


Please give your opinion and help me complete the project.

OK. Can you describe exactly how you are going to put the data into the microphone input?

with the help of a microcontroller

Oh this is such fun.

what do you mean by this

sidharthmadan said:

with the help of a microcontroller

Click to expand...

I do not understand your description. In our world of electronics, we communicate much more effectively using our own language. It is a graphical language, called the "schematic diagram". Can you describe exactly how you are going to put the data into the microphone input using a schematic diagram?

Microcontrollers cannot be directly connected to a microphone. What circuit are you going to use?