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Author Topic: Metal imaging system  (Read 2644 times)
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At what kind of speed do you want to get your results? You may be better off getting multiple channel external adc's and use spi,  then you'll be able to sample faster and do other things while the adcs sample,

This sounds like what I need.  Can I get hundreds of lead wires into this?  What's spi?

Thank you
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My biggest problem is how to plug hundreds of sensors into the arduino.

I suggest you need to get one sensor working and show that it does what you want before you worry about the practicalities of making a hundred of them.
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OK everyone seems to agree that I should build just one sensor.  I'm going to use electrical resistivity testing, instead of coils or Hall effect sensors.  Here are the schematics: http://www.state.nj.us/dep/njgs/geophys/elec.htm

Below is the code I'm using.  It's just a mix of Blink and AnalogRead.  The idea is to send the LED blink current through lead wires into the "ground" (I'm using a cup of water), and pick up the residual voltage through the AnalogRead AO wire.  I put a piece of metal in the cup to pick up the current and hopefully hold the charge long enough for the AO wire to measure a voltage.

It's not working.  All zeros on the serial monitor, except for a couple blips when I was jostling the cup around.
Code:
/*
  Blink
  Turns on an LED on for one second, then off for one second, repeatedly.
 
  This example code is in the public domain.
 */
 
// Pin 13 has an LED connected on most Arduino boards.
// give it a name:
int led = 13;

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.
  pinMode(led, OUTPUT);
  Serial.begin(9600);  
}

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);               // wait for a second
  int sensorValue = analogRead(A0);
  // Convert the analog reading (which goes from 0 - 1023) to a voltage (0 - 5V):
  float voltage = sensorValue * (5.0 / 1023.0);
  // print out the value you read:
  Serial.println(voltage);
}
 

Moderator edit:  the usual.


« Last Edit: December 08, 2012, 11:35:03 am by AWOL » Logged

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I don't think you connected the grounds, Dave.
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What sort of effect are you expecting to measure after a second?
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I put a piece of metal in the cup to pick up the current and hopefully hold the charge long enough for the AO wire to measure a voltage.

Is this a recognised detection technique? It does not strike me as a particularly promising approach.
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It should pick up residual voltage traces left in the metal object after the current is blinked off.
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Yes the electrical resisitivity and induced polarization techniques have been used for over a hundred years.  I think it started during the california gold rush.
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I don't think you connected the grounds, Dave.
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But after one second?
Really?
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It should pick up residual voltage traces left in the metal object after the current is blinked off.
That is pure rubbish. It is just snake oil, that is not how electricity works.
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But after one second?
Really?

I'm sure leaving it longer works better, but regardless, I'm not even picking up a signal when the charge is "live".
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It should pick up residual voltage traces left in the metal object after the current is blinked off.
That is pure rubbish. It is just snake oil, that is not how electricity works.

Rubbish?  http://en.wikipedia.org/wiki/Induced_polarization
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I just think my program is not working, or I don't have the leads hooked up in the right spots.
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That link is fine, how you are interpreting it is rubbish.
Terms like residiual voltage traces are pure rubbish as is the way you are testing it.
It dosn't work you said, that is not news, what would be news is if you got some sort of effect from that test. You are totally missunderstanding how geophysical measurements work.
These sorts of effects are observable in bulk ground measurements, not with a lump of metal in a cup.
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OP, I think you're confused about timescales.
One thousand milliseconds is one whole second.
Any effects you're likely to measure will be on the milli or micro second scale.
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I think you will need some pretty fancy analog processing before you even get to the arduino input, this is one of the reasons I gave up on the Proton magnetometer,  trying to dig the fading signal out of the noise after energising the target.
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