L
Lars Torben Wilson
- Jan 1, 1970
- 0
Hi all,
I recently posted about a bat detector (read ultrasonic pitch
downshifter) I'm building from the following schematic:
http://home.kabelfoon.nl/~bertrik/bat/simphet.htm
My goal is to build it without the indicated coils. Bob Eldred
showed me the light on getting rid of one of the coils, reminding
me that the 47mH coil and its cap were simply a passive LPF, which
I then replaced with an active Sallen Key LPF (TL072 and some
resistors/caps).
Now my detector works quite well. I can easily hear several
harmonics from my TV, my pocket chain clinking sounds REALLY
weird, etc. But I want to see if I can improve the bandwidth
of the piezo UST.
Bertik (author of the schematic) has a good page on how to
do this with caps, resistors, and a 5-8mH coil, but before
I get into trying to make the coil, I was wondering if there
are any active/non-coil ways to do it.
Any answers/tips/links appreciated,
Torben
P.S. I've googled/teoma'd/mootered for this a million times,
but either the answer's not out there or I didn't
recognize it for what it was.
I recently posted about a bat detector (read ultrasonic pitch
downshifter) I'm building from the following schematic:
http://home.kabelfoon.nl/~bertrik/bat/simphet.htm
My goal is to build it without the indicated coils. Bob Eldred
showed me the light on getting rid of one of the coils, reminding
me that the 47mH coil and its cap were simply a passive LPF, which
I then replaced with an active Sallen Key LPF (TL072 and some
resistors/caps).
Now my detector works quite well. I can easily hear several
harmonics from my TV, my pocket chain clinking sounds REALLY
weird, etc. But I want to see if I can improve the bandwidth
of the piezo UST.
Bertik (author of the schematic) has a good page on how to
do this with caps, resistors, and a 5-8mH coil, but before
I get into trying to make the coil, I was wondering if there
are any active/non-coil ways to do it.
Any answers/tips/links appreciated,
Torben
P.S. I've googled/teoma'd/mootered for this a million times,
but either the answer's not out there or I didn't
recognize it for what it was.