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peak detector design

Joe Wu

Feb 9, 2017
11
Joined
Feb 9, 2017
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11
Hi, I am building a peak detector and voltage comparator for my returning signal of the ultrasonic transducer.
Below are the circuit diagram of peak detector and voltage comparator:
voltage comparator.jpg peak detector.jpg
And below are the screenshot of oscilloscope after peak detector and voltage comparator:
upload_2017-2-21_11-3-29.png
upload_2017-2-21_11-3-46.png
As you can see, it kind of works, it detect the peak at the very beginning, however, what I am interested is the returning signal after the first pulse (the signal that appears in the middle of the screen), and my peak detector is not able to detect it.
Any idea about how to do it?
Thank you.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
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Jan 21, 2010
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25,510
Google for a peak and hold circuit if you want something that will hold the peak value better.

Then reset the hold very briefly after the pulse has been sent. Another option is to hold it in reset while the signal is sent, lifting the reset after a small delay.

In general, a MOSFET or a bjt across the cap will work pretty well as a reset.
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
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3,656
The duration of your peak detector is much too long for it to detect the return pulse. Shorten the duration by reducing the value of R1 to 47k or less. Then it will show the transmitted pulse, zero then the return pulse.
 

Joe Wu

Feb 9, 2017
11
Joined
Feb 9, 2017
Messages
11
The duration of your peak detector is much too long for it to detect the return pulse. Shorten the duration by reducing the value of R1 to 47k or less. Then it will show the transmitted pulse, zero then the return pulse.

I have tried, nothing changes. Thank you
 
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