near range ultrasonic communication

[wanchope]

Dear all,
I wanna design an ultrasonic circuit for near range communication. Let me refer it as 'Tag' at the moment. 2 meter tag-to-tag communication range is what i aim for.
There will be a transmitter and a receiver on the Tag. I have a referenced ultrasonic range finder circuit on my hand as attached.
Assuming both tags will transmit their IDs(basically square waves 0 & 1s) at random intervals.
My question is can one of the tags receive the square wave sent out by another tag using the receiving circuit?
Do I need any modulation for this kind of communication? And any hardware changes?

Thanks in advance.
Wanchope

 

[wanchope]

I also have some doubts for clarification.

1) why do most of the rangefinder circuits use two transducers (1 transmitter and 1 receiver)? I realize there is transceiver available. Why people always want to use 2 instead of 1? Any special reason I am not aware of?

2) Many designs use 40khz frequency? Why 25khz not as common?

Thanks.

Wanchope

 

[throwaway18]

My question is can one of the tags receive the square wave sent out by another tag using the receiving circuit?

I'm not familiar with the MSP processor you are using but it looks possible. Writing the software may be a bit tricky. If you need the micro to do other tasks while listening for signals you may need to do structure your software in a diferent way to the usuall do one thing, do somthing else, GOTO start-of-main-loop style. I'd consider feeding the receive signal into an interrupt pin and writing a state machine to do the detection and decoding.

That receiver circuit seems to be a zero crossing detector so it is likely to give a frequently changing output due to background noise.

I'd go for simple on/off carrier signalling with a nice long preamble. Tone detection in small microcontrollers has been discussed in other threads in this forum.

EDIT: spelling/typo

 

[wanchope]

Thanks, throwaway18.

I'd consider feeding the receive signal into an interrupt pin and writing a state machine to do the detection and decoding.

I will do the same.

That receiver circuit seems to be a zero crossing detector so it is likly to give a frequency changing output due to background noise.

Besides using preambling, any hardware modification can improve?

When you are talking about 'simple on/off carrier signalling', does it mean 1 = high, 0 = low at 40khz? Any coded method like Manchester coding, NRZ will help?

Thanks.

Wanchope

 

[throwaway18]

I mean 1=sending a 40KHz tone, 0=not sending a tone