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Please explain me this AD envelop plus moding question.
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RuiGomes



Joined: Feb 09, 2014
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Location: Almada

PostPosted: Sun Feb 09, 2014 4:39 am    Post subject:  Please explain me this AD envelop plus moding question. Reply with quote  Mark this post and the followings unread

Hello

I have build this envelop generator sometime ago and it works good for my needs. But the gate responds to 5V gate and i want to mode it to respond to 3V gates. Then i realized that i don't have any clue on how this schematic works...
Could someone be so kind and explain me this circuit and point me out were i should do the modification to achive my needs?

Posted Image, might have been reduced in size. Click Image to view fullscreen.
I don't remeber where i got this schematic, but i belive it was from here, years ago Smile

kind regards,
Rui
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PHOBoS



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PostPosted: Sun Feb 09, 2014 7:08 am    Post subject: Re: Please explain me this AD envelop plus moding question. Reply with quote  Mark this post and the followings unread

welcome Rui

ok let's see
The 2 NAND gates in the lower left corner (1/2 x 4011) are configured as a set/reset flip flop. If the bottom NAND get's a high to low pulse it's
output will go high and stay high untill the top NAND get's a high to low pulse. You're trigger signal will mostly likely be a low to high pulse so
there is an extra transistor inverter at the input, this also makes it possible to use a lower trigger voltage.

ATTACK:
When the output goes high the capacitor (1-10uF) get's charged through the diode and potentiometer at the top. The signal get's buffered and
amplified by the opamp which will be the output voltage. This voltage also goes to a comparator made with another opamp and when the voltage
reaches the treshold level (set with the 4K7 and 10K) resistor it's output will go high. This then get's inverted by another transistor and triggers the
top NAND.

DECAY:
When the output of the top NAND goes high the flip flop get's reset. As a result the output of the bottom NAND goes low and the capacitor get's
discharged through the potentiometer and diode at the bottom. Then buffered and amplified, the comparator output goes low and it's ready for
the next cycle.


I would suspect that it allready works with 3V but if it doesn't then you have to change the resistors at the trigger input. You can remove the 1K2
resistor and maybe decrease the value of the 100K on the base of the transistor. if that still doesn't work you could try experimenting with a
different value for the pullup resistor (100K connected to the NAND). Another thing is the diode on the input which causes a voltage drop, you
could leave it out if you always use a positive voltage for the trigger. Or use a schottky diode which has a lower forward voltage.

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elmegil



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PostPosted: Sun Feb 09, 2014 7:57 am    Post subject: Reply with quote  Mark this post and the followings unread

If it doesn't work with 3V it's likely because the transistor's not turning on, I would expect. Assuming a 15V supply, the divider for when it's on is going to drop the input to the flip flop to .2V, which ought to be plenty low, and that should be independent of the trigger voltage.

So the diode or possibly dropping the input resistor (though not too much, you don't want to muck up the input impedance) would be where I'd look.

Of course test it first, it ought to work with 3V too.
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RuiGomes



Joined: Feb 09, 2014
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PostPosted: Sun Feb 09, 2014 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the help guys!
the explanation was great! hopefully tomorrow ill have time to work on the circuit.
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fantozzi



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PostPosted: Sun Feb 16, 2014 9:30 am    Post subject: Reply with quote  Mark this post and the followings unread

once uppon a time i had the same problem, i found out that it is not possible to switch a higher Volatge (here the high level of ur NAND) with a lower voltage.
u have to use a levelshifter, a dual-inverting-transistor-switch
with the standard noninverting version is that not possible

example circuit, from http://www.mikrocontroller.net/topic/36812
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richardc64



Joined: Jun 01, 2006
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PostPosted: Mon Feb 17, 2014 7:03 am    Post subject: Reply with quote  Mark this post and the followings unread

fantozzi wrote:
... i found out that it is not possible to switch a higher Volatge (here the high level of ur NAND) with a lower voltage.

???

Where did you get that idea? It simply isn't true.

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Thomas_Henry



Joined: Jul 24, 2009
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PostPosted: Thu Mar 06, 2014 5:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

The input protection diode is in the wrong place. (As noted, it will create a drop as shown here).

Instead, connect it from the base of the transistor to ground (cathode to base, anode to ground).

And, there is nothing wrong with a lower voltage trigger switching a higher voltage on the transistor. A single transistor will do it.

Also, the circuit can be greatly simplified. I just posted an easier version over on the Thomas Henry section.

Thomas Henry
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Blue Hell
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PostPosted: Thu Mar 06, 2014 6:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

the link being : http://electro-music.com/forum/post-397258.html#397258 I guess.
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