Arduino Due analog output has 500mV offset

Question

I use a simple serial connection to tell the Due what to output into an analog output pin. However, the outputs are offset about 550mV (as seen on an oscilloscope) and the maximum value of 255 gives ~2.7V. What am I missing? Why can't the DAC output 0V - 3.3V mapped onto 0 - 255 values?

int output = DAC1; // analog output pin
String inData;
void setup()
{
 Serial.begin(9600);
}
void loop() {
 while (Serial.available() > 0) {
 char value = Serial.read();
 inData += value;
 if(value == '\n'){
 val = inData.toInt(); // 0..255
 analogWrite(output, val);
 Serial.println(val);
 inData = "";
 }
 }
}

• Ignacio Vazquez-Abrams: What is the voltage on VDDANA?
• aaaaa says reinstate Monica: how do I check that?
• Ignacio Vazquez-Abrams: With the black lead of the DMM on ground and the red lead on VDDANA, with the DMM in DC volts mode.
• aaaaa says reinstate Monica: it reads about 4.2V, if by VDDANA you mean Vin pin. I don't know where to measure VDDANA otherwise
• Ignacio Vazquez-Abrams: The datasheet for the MCU gives its pinout.

Answer 1

I don't know how old this thread is, anyway I thought it doesn't hurt to give some insight because I experienced the same problem. Look at: http://www.atmel.com/Images/Atmel-42187-ATSAM3X-and-ATSAM3A-Series-Checklist_AP-Note_AT03462.pdf page 13: DAC0 and 1 voltage lays between 1/6 ADVREF and 5/6 ADVREF which corresponds to approximately ADVREF=3.2v; Span is (4/6)*3.2 = 2.1v for periodic signals, Offset can be removed by using a small decoupling capacitor which will act as a high pass filter. Hope this helps

• aaaaa says reinstate Monica: Thank you for help! Numbers on atmega datasheet do make sense, they are close to what I see on oscilloscope.

Answer 2

int output = DAC1; // analog output pin
String inData;
int val; 
void setup()
{
 Serial.begin(9600);
}
void loop() {
 while (Serial.available() > 0) {
 char value = Serial.read();
 inData += value;
 if(value == '\n'){
 val = inData.toInt(); // 0..255
 val=constrain(val, 543, 2720);
 analogWrite(output, map(val,543,2720, 0, 255));
 Serial.println(val);
 inData = "";
 }
 }
}

• Greenonline: Hi and welcome. Please edit your answer and provide an explanation as to why your code works. Code only answers are frowned upon. Thanks.