Hi everyone!
I'm working on a DIY synth controller, sort of drum pad on which I could strike, but also rub, play with a violin bow...
The first idea is to use an arduino to capture data from piezos. But arduino isn't fast enough to capture "simultaneously" 8 audio signals and track the envelope. And I don't really anything else than the envelope for my purpose. So I prefer save arduino ressources to compite antrhing else than high sampling rate data.
So, what I'd like is to build an envelope follower between the piezo and the arduino ADC.
So I would make one from this basic one :
But I would like to improve it a bit if it keeps beeing quite simple.
What I'd like to add is a gain pot in the input of this follower, and a decay pot to be able to adjust the decay time of the envelope follower.
So I imagined this circuit. But I miss some skills to well understand everything. So I guess this could be better.
I've added an inverting amp at the input with a pot to control the gain. I guess this is OK. I've let the unity gain amp the same, with this 10Kohms resistor (R3) which I just don't know what it is for? And I replaced the 2Mohms restistor and 0.1µF cap by a standart 100Kohms pot (R4) and a 4.7µF cap (C1) to control the decay time.
But my question is : is that modifications still OK to enter the arduino ADC? Is the impedance OK? WOuld there be something better to do? Simpler?
Thank you very much for your help!
Cheers,
Fred
I'm working on a DIY synth controller, sort of drum pad on which I could strike, but also rub, play with a violin bow...
The first idea is to use an arduino to capture data from piezos. But arduino isn't fast enough to capture "simultaneously" 8 audio signals and track the envelope. And I don't really anything else than the envelope for my purpose. So I prefer save arduino ressources to compite antrhing else than high sampling rate data.
So, what I'd like is to build an envelope follower between the piezo and the arduino ADC.
So I would make one from this basic one :
But I would like to improve it a bit if it keeps beeing quite simple.
What I'd like to add is a gain pot in the input of this follower, and a decay pot to be able to adjust the decay time of the envelope follower.
So I imagined this circuit. But I miss some skills to well understand everything. So I guess this could be better.
An externally hosted image should be here but it was not working when we last tested it.
I've added an inverting amp at the input with a pot to control the gain. I guess this is OK. I've let the unity gain amp the same, with this 10Kohms resistor (R3) which I just don't know what it is for? And I replaced the 2Mohms restistor and 0.1µF cap by a standart 100Kohms pot (R4) and a 4.7µF cap (C1) to control the decay time.
But my question is : is that modifications still OK to enter the arduino ADC? Is the impedance OK? WOuld there be something better to do? Simpler?
Thank you very much for your help!
Cheers,
Fred
Last edited:
Thank you! Seems the attachment didn't work correctly. I uploaded the file again and updated so you should be able to see and open it.
Why have you drawn a zener diode instead of a normal signal diode?
You may need to review the bias arrangements for a single-supply-rail opamp. I don't know what the 10k resistor is for, but I suspect it is an attempt at input bias.
Bear in mind that no envelope detector can follow an arbitrary envelope perfectly, so you need to think about attack time and decay time. The capacitor cannot charge up instantaneously, as the previous stage can only supply a finite current. I would use a smaller cap than 4.7uF, and if necessary add a buffer after it.
You may need to review the bias arrangements for a single-supply-rail opamp. I don't know what the 10k resistor is for, but I suspect it is an attempt at input bias.
Bear in mind that no envelope detector can follow an arbitrary envelope perfectly, so you need to think about attack time and decay time. The capacitor cannot charge up instantaneously, as the previous stage can only supply a finite current. I would use a smaller cap than 4.7uF, and if necessary add a buffer after it.
Short answer: that schematic does not work at all so forget it.
Search for single supply envelope followers.
If nothing better, take a hard look at "Auto Wah" guitar pedals, they use an envelope follower to modulate bandpass filters and, by definition, are designed for single supply 9V because they are supposed to run on battery power; adapting them to just 5V is a reasonable task.
Here´s one: notice the FET input, needed by the high impedance Piezo capsule, single supply operation, LM358 will work properly with just +5V supply, take your Arduino signal across the "range" pot, which can be a 22k fixed resistor instead.
Also use a conventional diode, say 1N914/1N4148 instead of the Red Led rectifier and replace 1N914 at the right with a wire link.
You may use the now unneeded second half of LM358 as a unity gain buffer if you wish, with +IN connected straight your output resistor hot pin, LM358 can read and follow 0V/ground voltages with no problem at all.
Search for single supply envelope followers.
If nothing better, take a hard look at "Auto Wah" guitar pedals, they use an envelope follower to modulate bandpass filters and, by definition, are designed for single supply 9V because they are supposed to run on battery power; adapting them to just 5V is a reasonable task.
Here´s one: notice the FET input, needed by the high impedance Piezo capsule, single supply operation, LM358 will work properly with just +5V supply, take your Arduino signal across the "range" pot, which can be a 22k fixed resistor instead.
Also use a conventional diode, say 1N914/1N4148 instead of the Red Led rectifier and replace 1N914 at the right with a wire link.
You may use the now unneeded second half of LM358 as a unity gain buffer if you wish, with +IN connected straight your output resistor hot pin, LM358 can read and follow 0V/ground voltages with no problem at all.
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