ADC Unstable under 1.5V input

Discussion in 'Troubleshooting' started by oregon187, Feb 26, 2014.

  1. oregon187

    oregon187 New Member

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    I have tested two different UDOO boards now and the results have been the same. The analog to digital converter does not turn on until an input of 700mV and it is very unstable until the input reaches 1.5V (I tested several different analog input pins also, with the same results). I tested an Arduino Uno and an Arduino Due as well. The Uno and the Due both returned accurate linear results. For the test procedure I used a potentiometer connected to the 3.3V output of the UDOO (which actually tops out at 3.441V) and a common ground between all boards tested. The ADC resolution was left at the default of 10 bits, so the digital output should have been between 0 and 1023. Here is the code I used on all boards:

    Code:
    int sensorPin = A0;    // select the input pin for the potentiometer
    int ledPin = 13;      // select the pin for the LED
    int sensorValue = 0;  // variable to store the value coming from the sensor
    
    void setup() {
      // declare the ledPin as an OUTPUT:
      pinMode(ledPin, OUTPUT);
      Serial.begin(115200);  
    }
    
    void loop() {
      // read the value from the sensor:
      sensorValue = analogRead(sensorPin);
      // turn the ledPin on
      digitalWrite(ledPin, HIGH);
      // stop the program for <sensorValue> milliseconds:
      delay(1000);
      Serial.println(sensorValue);
      // turn the ledPin off:
      digitalWrite(ledPin, LOW);
      // stop the program for for <sensorValue> milliseconds:
      delay(1000);
    }
    The only difference in the setup with all the boards is the IDE. I used the Arduino 1.5.4 IDE on the UDOO to program the onboard Sam3X chip and I used the Arduino 1.5.6 IDE to program the Uno and Due from a Linux PC.

    I have attached a picture of the test results.



    Is this a flaw in the design of the UDOO board? Or is it possible that the boards that I have happen to have the exact same problem (perhaps a bad batch or something along those lines)?
     

    Attached Files:

  2. oregon187

    oregon187 New Member

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    I have now tested a 3rd UDOO board and it performed just like the other two UDOO's. Also, the fact that the Atmel chip heats up even under light usage as many other forum posts have stated, points to a possible design flaw in the UDOO board.
     
  3. delba

    delba Administrator Staff Member

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    Thanks for the heads up oregon187, we'll definitely run some tests.
     
  4. oregon187

    oregon187 New Member

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    Also, I don't know if this is relevant, but we are not able to program the arduino side of the UDOO from a PC the way it is described in the tutorial section, regardless of the presence of J18. With J18 removed, I am able to open the Arduino IDE serial monitor to the device from a PC, but trying to actually upload code gives a device not found error.
     
  5. oregon187

    oregon187 New Member

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    :D Okay, today I received the fourth UDOO that my university had me order. I tested it using the onboard Arduino compiler and I got the same non-stable results as the other three.

    However, I was able to program this one using my Linux PC and the results were much different. The readings were linear just like they should be and just like the Uno and Due boards. I then tested one of the other boards that I received a few months ago and this time, programming it from my PC worked (not sure why I could never get it to work before :? ). Anyway, the older board showed the good linear results as well.

    My conclusion is that there is something wrong with the Arduino IDE compiler for the UDOO board and not with the UDOO hardware.

    This is definitely a relief, software is much easier to fix/work-around than hardware.

    Thanks for all the help on this.

    Is there a good way to find out the differences between the UDOO Arduino IDE v. 1.5.4 and the PC Arduino IDE v. 1.5.6? There is a lot of source code to compare with no direction.
     

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