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Take a look at the attachment. You use two pins, and alternate their 
values, 01 -> 10 -> 01 -> 10 ... etc

Thus, when side A of the transducer is 0, side B is 12V. When it 
changes, side A = 12V, side B = 0V.

In your case, if you consider the grounded side, and the waveform as an 
AC waveform in relation to it (which is what the transducer sees,) it 
goes from 0 to 12 to 0. Thus, if you look at it as an AC waveform, its 
12V peak-to-peak.

If, on the other hand, you use two driver pins, then from the point of 
view of one of the pins, the other guy's voltage is 12 above, then 12 
below, then 12 above, so the AC waveform has a 24V peak-to-peak value. 
Thus, it'll deliver twice as much power into the load.

To me, it sounds like you are doing the right things. Do you have any 
test equipment at all? An oscilloscope would tell you what you need to 
know in about 20 seconds. Send your schematic, and maybe we will see 
something.

Regards,
 Bob Monsen


Wan Zulhelmi Wan Ahmad Kamar wrote:

>Hi, sorry again, I can't seem to understand the part where both bob
>and colin said that to drive the tx, use push and pull.  Bob said that
>use two PIC pins on each transducers pin and pull one up as the other
>goes down?.
>
>Does that means for example, my sender transducer would have the
>ground pin connected to ground with the signal pin connected to two
>i/o port on the PIC?
>
>This is my so-called schematics for the transmit
>                                      12V
>                                        |  
>                                        | 
>                                       r2 = 1k
>                                        |
>                                        ----------------transducers
>                                       /
>                                      /
>PIC RA0 ---- r1 = 1k --------|
>                                      \
>                                       \
>                                        |
>                                        Ground 
>
>RA0 is on and off through bsf PORTA, RA0 and bcf PORTA,RA0
>
>Sorry, if this seems to dumb of a question
>Thanks a lot
>
>>From = wan
>
>On Sat, 25 Sep 2004 19:45:09 -0700, Robert Monsen <rcmonsen@comcast.net> wrote:
>  
>
>>I bought some of those recently from goldmine. I played with them with
>>my oscilloscope and signal generator, and found that they were resonant
>>at something over 41kHz instead of 40kHz.
>>
>>To drive them, use two PIC pins on each transducer pin, and pull one up
>>as the other goes down, and vice-versa. That will make the effective
>>swing across the transducer Vcc*2. Remember that 40kHz means a 12.5us
>>transition. However, since the transducers are resonant at a higher
>>frequency, just wait 12us, which is easier with a 1MHz instruction
>>clock. Note that the higher the voltage swings, the higher the power
>>output (up to a point) so if you use a couple of NPNs or N-MOSFETs and a
>>12V supply, you'll get a more powerful signal.
>>
>>For receive, you can either build an amplifier and a bandpass filter, or
>>use something like an LM567 "Tone Decoder" chip. The LM567 is a phase
>>locked loop that will detect a signal with fairly low power.
>>
>>With a 5V signal (10V PP input), I was bouncing the signal off of the
>>ceiling (about 3m round trip) and getting a return signal of something
>>like 20mV peak-to-peak (shown on my Tek 475 oscilloscope). Thus, if you
>>are trying to detect this with a PIC, for example, you are going to be
>>out of luck without some amplification and filtering.
>>
>>Regards,
>>Bob Monsen
>>
>>
>>
>>cdb wrote:
>>
>>    
>>
>>>Hi,
>>>
>>>First you forgot the EE tag so many people on the list may not have
>>>received this message if they filter their mail.
>>>
>>>
>>>:: Hi, I'm currently using Ultrasonic transducer to send a 40 khz
>>>:: signal.
>>>:: I'm having a problem of transmitting the send at distance of 1m -
>>>:: 3m.
>>>:: I can send the signal at only 10-20 cm which is a joke..  Anybody
>>>:: got
>>>:: any idea or should i go buy another transducer.
>>>::
>>>:: I;m using MA40A3R/S - R/s is receiver/sender.
>>>
>>>I would think the problem lies either in the Tx not being powerful
>>>enough or more likely the Rx is not sensitive enough.
>>>
>>>You don't say what you are using to modulate the Tx and what you have
>>>in the way of amplification for the Rx.
>>>
>>>You may also need to add in some sort of filtering to help the Rx
>>>avoid spurious signals.
>>>
>>>To increase the Tx output you can drive the sensor in a push pull
>>>configuration; so while the top terminal is at +v the bottom is at 0v
>>>and then reverse the sequence.
>>>
>>>Colin
>>>
>>>
>>>
>>>
>>>
>>>
>>>      
>>>
>>_______________________________________________
>>http://www.piclist.com
>>View/change your membership options at
>>http://mailman.mit.edu/mailman/listinfo/piclist
>>
>>    
>>
>_______________________________________________
>http://www.piclist.com
>View/change your membership options at
>http://mailman.mit.edu/mailman/listinfo/piclist
>
>  
>

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