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View Code? Open in Web Editor NEWFunctions for many of the ADC capabilities of the ATSAMD21 series.
Functions for many of the ADC capabilities of the ATSAMD21 series.
I'm not quite clear if this is a bug or if I'm missing something here, any help to get to the bottom of this would be great.
Is there any way to obtain a true 12bit differential result using analogDifferential()
?
For instance if we do a single ended analogRead of a 3V input the 12bit ADC result is the expected ~3720 (of a max 4095).
Simply switching ADC->CTRLB.reg
to CTRL DIFFMODE
and setting the MUXPOS/MUXNEGs, then applying 3V of difference between these differential inputs, produce half of the expected value. The reference is unchanged in both cases and is the default analogReference(AR_DEFAULT)
which should be 3.3V. If I change the reference to not do a DIV2 then the result saturates to 2047 (11bit).
In this Arduino forum post you seem to suggest the true 12bit value in differential reads is still available but I could not find a way to obtain it. Or maybe differential mode shifts the reference to half of whatever it is set to, and then yields a signed 12bit (11bits + 1 sign bit) result from that? That would seem quite wrong.
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);
}
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