Multiple ADC differential measurement

[Shille88]

I have ran into a problem which I have tried to find the cause for, but not being able to.

I am trying to establish 3 ADC differential channels (tot. 6 pins) for measuring 3 different analog signals. However this is not working if I have all the three analog signals connected to the 3 ADC differential channels.

If I disconnect all the analog signals. Connect only one at a time and measure it, and disconnect the signal after measurement, then all the three ADC differential channels will work. See detailed explanation below, AS# = Analog signal ADCD# = ADC differential (each channel has 2 pins)

// Results of all three ADC are wrong AS1 - connected - ADCD1 AS2 - connected - ADCD2 AS3 - connected - ADCD3

// Works Step 1 AS1 - connected - ADCD1 AS2 - disconnected - ADCD2 AS3 - disconnected - ADCD3

Step 2 AS1 - disconnected - ADCD1 AS2 - connected - ADCD2 AS3 - disconnected - ADCD3

Step 3 AS1 - disconnected - ADCD1 AS2 - disconnected - ADCD2 AS3 - connected - ADCD3

My code: /* Name: AdcDifferential.ino Created: 11/16/2020 9:26:38 AM Author: SherjeelTon */

#include "ATSAMD21_ADC.h";

#define Negative1 A0 #define Positive1 A3

#define Negative2 A4 #define Positive2 A6

#define Negative3 A5 #define Positive3 A7

int16_t signedResult; float result; float voltRef = 2.048; float elevenBitResolution = 2047; float fifteenBitResolution = 32767;

// the setup function runs once when you press reset or power the board void setup() { Serial.begin(9600); analogReference2(ADC_REF_VREFA); analogReadExtended(16); analogPrescaler(ADC_PRESCALER_DIV512); analogGain(ADC_GAIN_1); analogCalibrate(); }

// the loop function runs over and over again until power down or reset void loop() { signedResult = analogDifferential(Positive1, Negative1); result = signedResult * voltRef / fifteenBitResolution; Serial.print("Channel 1: "); Serial.println(result, 6); delay(1000);

signedResult = analogDifferential(Positive2, Negative2);
result = signedResult * voltRef / fifteenBitResolution;
Serial.print("Channel 2: ");
Serial.println(result, 6);
delay(1000);

signedResult = analogDifferential(Positive3, Negative3);
result = signedResult * voltRef / fifteenBitResolution;
Serial.print("Channel 3: ");
Serial.println(result, 6);
delay(1000);

}

[Molorius]

I realize this is is over a year old, were you able to figure out the problem? Do you still need help with this?

[Shille88]

No, I never figured out how to solve this problem. I tried to find out if it was a problem within the library or the hardware itself but i didn't get so far.