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16  Using Arduino / General Electronics / Re: Arduino Uno ADC input inpedance on: July 30, 2012, 04:10:45 am
The ADC inputs are intended for source impedances of 10k or less.

Thanks for the info Leon. My callsign is k4wde
17  Using Arduino / General Electronics / Re: Arduino Uno ADC input inpedance on: July 30, 2012, 03:38:25 am
Wow, thanks Mike.  I haven't programmed in over 20 years.  Getting old isn't for sissies.  LOL
Thought I'd take it up again as a hobby in my old age. Maybe I should try boxing.  heheh

Walt
North Carolina
18  Using Arduino / General Electronics / Re: Arduino Uno ADC input inpedance on: July 30, 2012, 03:04:23 am
Interesting.  I just started learning how to use the LCD library yesterday.  The example that I got somewhere (hehehe, that's the problem) the author wondered why pin 14 was used, as it had no effect on LCD operation.
I just changed the sketch to A5 and everything works as it should.  510 of 1023 on the LCD and 2.5 volts at the center of the divider with the Fluke 77. So I guess I've got to figure out how to properly use the LCD library now.  LOL
And my ignorance of the Arduino must be showing also as there is no Pin 14 silk screened on the board. So I'm wondering how you figured this one out.  In any event, thanks a lot.

Walt
North Carolina
19  Using Arduino / General Electronics / Re: Arduino Uno ADC input inpedance on: July 30, 2012, 01:13:26 am
Well, here's my problem.  I got rid of the 10 k pot just in case it was flaky.  I replaced it with two 220 ohm resistors in series across the 5V and ground of the arduino. With the A0 pin not connected to the junction the junction measures close to 2.5 volts as expected.  When the A0 lead is connected the voltage across the bottom resistor drops to .4 volts!!!! To say I'm bumbfuzzled about this result would be a mild understatement. Obviously something is going on here that I'm not aware.

Resistance of both resistors measured with Fluke 77 at 221 ohms. Same fluke was used to measure the DC voltage at the junction of the resistors.

This is the simple sketch I'm running on the arduino:

Code:
#include <LiquidCrystal.h>  // I have a LCD connected to display the result

LiquidCrystal lcd(12, 14, 11, 7, 8, 9, 10);

int sensorPin = A0;    // select the input pin for the
int sensorValue = 0;  // variable to store the value coming

void setup()
{
lcd.begin(16,2);
lcd.setCursor(0,0);
}

void loop()
{
  
 sensorValue = analogRead(sensorPin);
  lcd.clear();
  
  lcd.print(sensorValue);
  delay(100);  
}


I must be making some mistake with this sketch.  I can't see it. LOL

Walt
North Carolina


Moderator edit: [code] [/code] tags added.
20  Using Arduino / General Electronics / Arduino Uno ADC input inpedance on: July 29, 2012, 11:42:44 pm
Just starting out on the Arduino Uno v3.  After playing around with a 10k pot wired from 5V to Gnd, with the wiper attached to A0, some of the results are a bit puzzling to me. I'm wondering just what the input impedance of the ADC portion of the Arduino presents to the outside world. I'm seeing much more effect on the variable voltage divider created by the pot than I would have expected.

Also I'm starting to think that the A0-5 pins might just be one ADC being multiplexed. I would get very jiggly readings on analogReads until I introduced a delay of 100 miliseconds in the loop. I guess I was expecting much more from this inexpensive chip than it was prepared to provide.  LOL

Thanks;
Walt E.
North Carolina
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