Arduino Due: ADC gain adjustment problem

Question

I want to increase gain of the ADC channel. To achieve this I'm using adc_set_channel_input_gain function from adc.h. Here is the entire sketch:

const byte aPin = A6;

void setup() {
  analogReadResolution(12);

  // Configure ADC gain
  // Arduino/hardware/arduino/sam/system/libsam/include/adc.h
  adc_channel_num_t ch = (adc_channel_num_t)(g_APinDescription[aPin].ulADCChannelNumber);
  adc_set_channel_input_gain(ADC, ch, ADC_GAINVALUE_3);
  Serial.begin(9600);

  // Delay for serial stabilization
  Serial.println("Begin.");
  delay(2000);
}

void loop() {
  int analog = analogRead(aPin);
  Serial.println(analog);
  delay(500);
}

The problem is that output values are not depending on the gain value.

The function adc_set_channel_input_gain() is not compliant with the basic analog input library which use only analogReadResolution() and analogRead(). Please read more about adc_init(ADC... for the "sam3x". — J. Piquard
– J. Piquard, Commented Dec 8, 2016 at 21:44
@J.Piquard, thank you for help, where can I find documentation? — kelin
– kelin, Commented Dec 8, 2016 at 23:04
Take a look to that Guide: "Quickstart guide for SAM ADC driver". — J. Piquard
– J. Piquard, Commented Dec 8, 2016 at 23:17

kelin · Accepted Answer · 2016-12-21 22:52:29Z

Well, the solution was very simple. We just need to call adc_enable_anch() before changing gain or offset of the ADC. I improved my setup and the sketch works as expected now:

void setup() {
  analogReadResolution(12);

  // Configure ADC gain
  // Arduino/hardware/arduino/sam/system/libsam/include/adc.h
  adc_channel_num_t ch = (adc_channel_num_t)(g_APinDescription[aPin].ulADCChannelNumber);
  adc_enable_anch(ADC); 
  adc_set_channel_input_gain(ADC, ch, ADC_GAINVALUE_3);

  Serial.begin(9600);

  // Delay for serial stabilization
  Serial.println("Begin.");
  delay(2000);
}

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