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Author Topic: Any idea??? Multiple Piezos as sensor with Mux Shield  (Read 583 times)
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hello,

I am looking for helps here.
Any feedbacks or suggestions would be so helpful and great since I am not really familiar with using Arduino and sensing system.

I am working on a prototype for a sound installation. 
I've got 6 of 4' by 4' wooden platforms that underneath of each platform has 4 piezo transducer sensors and one contact mic.

the contact mic is for MOTU inputs, and other 4 piezo sensors (https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_1956776_-1) that wired to Mux shield  (http://www.sparkfun.com/products/9832) as 24 analog inputs. I refer to the Arduino circuit diagram called "Knock "(http://www.arduino.cc/en/Tutorial/Knock) basically 1M ohm for each inputs. Also, I am using Mux Shield Anlog Input sketch for reading sensors. (http://mayhewlabs.com/code/Mux_Shield_AnalogIn_Example.pde)

So on my breadboard, there are 24 piezos x 1M ohms and connect to analog inputs(mux 0 and mux 1) and all shared the same ground.

Then,  I have faced two problems.

1) When I only worked with Arduino(only 6  analog inputs) without Mux shield, i get some values when i knock the platform; however, when i use Mux shields (more piezos are hooked up), the values are very small range to use.  For example, Mux0 the first 4 inputs worked, but nothing else, everything else says 0.

2) I have heard that piezo wire voltages could drop out if the wire is 16ft long, so I try to use Operational Amplifier,
but it doesn't seem to work at all with Mux Shield.

So I don't know where to start debugging this.
I am happy to think about Arudino Mega, If this could be the best solutions. But again, not sure whether that will be the best solutions,
and I have to reduce inputs.

Thank you for reading this long concerns. I  looked through the forums on Piezo pre Amplifier circuit, but not sure how I can even start.
Partially, I think i don't understand the mechanism enough.
I really appreciate your inputs. Once again, thank you so much.
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Georgina Ontario
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You should post your code.

The people can look at it.
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Just another Hacker

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 IMHO, multiplexers chips have a big pass-trough capacitance, that with high impedance source
 could significantly drop amplitude of signal.

I download a Mux Shield schematic and find out that there is no option to bias  
output/input pin  with DC offset VCC/2, as recommended by chip maker, at least all their performance testing was done so. Not going deeply in CMOS operation specific,
there are two solution:
- bias input/output with VCC/2;
- OP amplifier before mux, you says it doesn't works, please show schematic and type OP
you try with. OP has to be high input resistance (FET input stage) 1Mohm and above.
 
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