Any idea??? Multiple Piezos as sensor with Mux Shield

Other Hardware Sensors
1

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 (Mux Shield II - DEV-11723 - SparkFun Electronics) 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.

2

You should post your code.

The people can look at it.

3

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.