Why not modulate the ultrasonic frequency with an audio tone.  4
seperate tones for the 4 seperate transmitters.

Wan Zulhelmi Wan Ahmad Kamar wrote:

>Hi,
>I'm creating an ultrasonic tracking device in which i have 4
>transmitter and 1 receiver.  For that i will need to create an ID for
>the receiver to distinguish where it is coming from.  Basically, from
>there, i will calculate the time difference betwen the transmitter to
>locate the position.
>
>Anyway, my question, how can i distinguish the id for the receiver
>part?  I was thinking of putting a constant delay for each transmitter
>to transmit but how can I make sure my PIC18f252 produce an exact
>delay of a certain millisecond or something.  It would need to be
>exact isn't it?  Therefore, looping to create delay is out of the
>question.
>
>Another thing, on the transmitter part, how do i send the id?  I was
>thinking about sending bit by bit but that would take up lots of
>coding..  Any suggestions?
>
>Do you guys think I need to implement Hamming Code for the code
>correction or is that only applicable to RF design?
>
>Thank you in advance.
>
>>From - Wan.
>
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