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.

• J. Piquard: 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".
• kelin: @J.Piquard, thank you for help, where can I find documentation?
• J. Piquard: Take a look to that Guide: "Quickstart guide for SAM ADC driver".

Answer 1

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);
}