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 Forum index » DIY Hardware and Software » Developers' Corner
line audio -> gate
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stoopid



Joined: Apr 06, 2009
Posts: 7
Location: holland

PostPosted: Thu May 24, 2012 2:36 am    Post subject: line audio -> gate Reply with quote  Mark this post and the followings unread

hi folks!

for a small project, i'd like to convert sine signals from max/msp to 0-5v gate signals, using a cheap usb sound card.

does anybody know what kind of circuit would work best for this?

I'm guessing to work from a schmitt-trigger?

help is much appreciated!
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PHOBoS



Joined: Jan 14, 2010
Posts: 1524
Location: Moon Base
Audio files: 319

PostPosted: Thu May 24, 2012 7:01 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm guessing you are going to need two circuits, because the signal will probably be very low so you'll
have to amplify it first. (simple opamp amplifier can do this). The second circuit is what you actually need to
convert it to a gate signal and is a comparator. You can find some usefull info about that one here.

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stoopid



Joined: Apr 06, 2009
Posts: 7
Location: holland

PostPosted: Sat May 26, 2012 5:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for that Phobos,

I came across this in another forum: a 'diode-pump' & comparator based circuit. Being noobish, i'm having a hard time judging, what do you guys think?

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Cheers!
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PHOBoS



Joined: Jan 14, 2010
Posts: 1524
Location: Moon Base
Audio files: 319

PostPosted: Sun May 27, 2012 4:55 am    Post subject: Reply with quote  Mark this post and the followings unread

stoopid wrote:
Thanks for that Phobos,

I came across this in another forum: a 'diode-pump' & comparator based circuit. Being noobish, i'm having a hard time judging, what do you guys think?

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Cheers!

Depending on the level of your input signal this should work. If it's low it shoud still work but only a
small part of the pot will be usefull, which might make it a bit harder to adjust. Since you allready
need an opamp for the comparator (unless you're using a real comparator chip but the's not necessary
for this purpose) I'd say use a dual version and use one of them to amplify the signal. You could
add a pot for gain control so you can use it for a wide range of input levels.

btw If I'm correct the 2.2uF in this circuit will give it a slow responce time. It actually looks similar to a
circuit used for sound controlled lights. (Add a LED to the ouput and it'll blink to the music)

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stoopid



Joined: Apr 06, 2009
Posts: 7
Location: holland

PostPosted: Sun May 27, 2012 10:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Cool, thanks

I guess i'll just have build the thing, maybe on breadboard first, this way I can swap some caps and see the response.

Another simple circuit I stumbled upon is this thingie

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Looks even simpler, I guess the RL is a pull-up?
Too bad there are no resistor values mentioned.

Any clue on how to figure those out?

Cheers!
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PHOBoS



Joined: Jan 14, 2010
Posts: 1524
Location: Moon Base
Audio files: 319

PostPosted: Sun May 27, 2012 11:47 am    Post subject: Reply with quote  Mark this post and the followings unread

yes, breadboard and experiment Smile

Here's a simple test you can do with a comparator circuit:
Take two pots (100K) that you connect between your supply voltage rails with the wiper of one pot attached to
the non-inverting input of the opamp (+) and the wiper of the other one to the inverting input (-). Add two LED's
to the ouput of the opamp. One between the ouput and the positive supply rail (with series resistor) and one
between the output and negative supply rail (also with a series resistor). Now put one pot in the center position
and turn the other one both ways. Watch what happens,. now do the same thing but with the other pot in the
center position. You can try different positions and it should be pretty clear what it does. And what size
resistors are usefull.

As for the RL, those examples use a real comparator with an open collector output so it can only sink.
(pull to ground) This means that anything you want to control has to be between the ouput and the positive rail
and that's RL (L stands for Load). But yeah you could also put a pullup resistor there in case you want to control
some CMOS chips.

One more thing. you say you want 0-5V gate signals, a standard opamp might not work very well with
such a low voltage, so you should power it from a higher voltage (say 12V=) and use a resistor zenerdiode
combination or an extra transistor. I might draw something up since I'll be needing something like it in the future Wink

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stoopid



Joined: Apr 06, 2009
Posts: 7
Location: holland

PostPosted: Mon May 28, 2012 1:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

nice!

might give that led trick a try!

I ordered the components today for the first circuit,

i'll post my findings!

cheers
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