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Old 14th September 2008, 04:07 PM   #1
Dogue is offline Dogue  United States
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Default Pressure sensor to control amplitude

There's probably an easy solution to this:

How do I use a pressure sensor (which would normally operate either at 4.5 / 5V) to control the output amplitude of a simple Panasonic electret condenser microphone circuit?
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Old 13th October 2008, 12:20 PM   #2
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Default Pressure sensor

Why?

What use would this be for?

There are "Strain Guages" used in bathroom scales that would work,but the circuitry could be a bit tricky.

You might want to go over to www.nutsvolts.com because this is kinda 'esoteric'.
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Old 13th October 2008, 04:00 PM   #3
Dogue is offline Dogue  United States
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Why? A simple microphone -> effects -> speaker -> instrument body -> microphone feedback loop, with the amplitude of the mic output being controlled by the (breath) pressure sensor. I have to believe this is exceedingly easy; the purpose shouldn't matter too much.
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Old 13th October 2008, 08:55 PM   #4
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Simplest way is probably something along the lines of an optical compressor
Pre-Amped microphone audio signal through a light-dependant-resistor to whatever its destination (mixer, recorder etc). Or stick the LDR into the 'insert' patch point on a mixing desk.
Presure sensor signal - amplified if necessary - to an LED., which is physically in close contact with the LDR.

Depends a lot on the exact output signal from the presure sensor.
Strictly speaking, a microphone is a pressure sensor too.
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Old 13th October 2008, 09:51 PM   #5
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I messed around with pressure sensors a bit. Typically the ones I used were in the range of about an atmosphere or so. You can register on these by blowing (like to inflate a balloon) into a tube attached to the port. You can get them for smaller values too, but they typically have a small entry port, and I don't think you'll get the effect you're looking for.

That said, pressure sensors are usually arranged in a wheatstone bridge. If I wanted to run a volume control off a pressure sensor, I'd be taking the voltage generated by the bridge and using it to control a voltage controlled amplifier, or you could read it with the A/D on a PIC micro and use that to control a digital potentiometer.

It's not trivial to figure out the exact details of how to arrange the gain and offset trimming in the first case and it's similarly not trivial to program the PIC. It's not monumentally difficult tho' and you should be able to get a prototype circuit together by reading up a bit on the web. If you post it here someone will critique it for you...

w
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Old 15th October 2008, 11:22 PM   #6
Dogue is offline Dogue  United States
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Thanks for the replies.

Perhaps I've been underthinking this.

But what I've been thinking is something like this:

A Honeywell ASDX series pressure sensor replaces the pot in an LM386-based amplifier (if necessary using a circuit like the one combining the pot and pressure sensor at the bottom of the page here: http://music.columbia.edu/~douglas/p...d.sensors.html).

I've tested the the pressure sensor using the CREATE USB Interface as well as the uHID interface and it works great for converting breath pressure to USB.

So, the question is, am I able to replace the pot in a low-power LM386-based amplifier with the pressure sensor-based circuit?

And if so, is this the easiest way to control audio amplitude with the pressure sensor?
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Old 15th October 2008, 11:22 PM   #7
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To clarify, the output of the particular pressure sensor ranges from 0.5V at no pressure applied to 4.5V at maximum pressure applied.
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Old 15th October 2008, 11:22 PM   #8
Dogue is offline Dogue  United States
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Quote:
Originally posted by Steerpike
Presure sensor signal - amplified if necessary - to an LED., which is physically in close contact with the LDR.
That actually seems like a good solution -- should be quite simple to build. Thank you.
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