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Having Trouble with Serial Monitor Average

e14 Contributor

I have a load cell hooked up to a strain meter, which is then output in to the arduino. I have 8 pounds applied to the load cell and that equals .80 volts read into the analog output pin. Of course, when I read it on the serial monitor, it isn't a constant .80 volts as it fluctuates because of noise. I have tried to average the serial monitor to get a better read to as close to .80 volts as I can get. Here is part of the code that I'm working with right now:

[code]

int sensorValue = analogRead(sensorPin);

 

  long sum = 0;

 

  float voltage = sensorValue * (5.0 / 1023.0);

 

  for(int i=0; i< 5; i++)

  {

    sum = sum + sensorValue;

 

    float voltage = sum / 1023;

   

    delay(300);

  }

 

  Serial.println(voltage, 3); 

[/code]

I changed the delay 3 times (300ms 1sec and 1 min) and then took a sample size of about 200 from the serial monitor and posted it on an excel spreadsheet to take the average. The average was always around .80V which is what I want, but the max and min are not close to .80V. There really is not difference between the 3 time intervals I've done. The max - min of each sample of each time interval is about .40V. It seems like the serial monitor is just printing out the voltage it reads after the delay instead of taking the average. I figured that if I took the average, the number it prints should be roughly the same each time. After having it average for a minute, there would be times where it would print .835V and then .795V (rough estimate). Is my code not really taking the average? Thank you for taking the time to read this.

  • 0

    Hi Edward,

     

    I'm guessing (not very knowledgeable with Arduino) but it looks like you are defining a variable outside the loop (float voltage) but also inside the loop too. If you declare it inside the loop, then it is possible that it disappears and is not what you're printing outside the loop at the end of your code.

    I think the code in the loop needs the word 'float' removed basically.

     

    However, I didn't really understand how the loop was performing an average, if the value was read from the ADC just once when you issued the analogRead(sensorPin) statement.

    In your loop, the delay is therefore having no effect except just delaying to reach the same outcome as if there was no delay.

    So, I think you meant for the analogRead command to be inside your loop.