AnalogReference for the Seeeduino Xiao

[jrdoner]

I am working on a fire detection system with the Seeeduino Xiao board. I have a thermistor attached, and so I'm reading a voltage which provides me with a temperature, after some mathematical juggling.

However, I find that the analogRefernce() function won't compile: the compiler claims that EXTERNAL, INTERNAL, or DEFAULT are not declared within the scope of the code. Also, I don't find any reference anywhere to an ARef pin, as exists on many Arduino variants.

So the XIAO appears to have a fixed ARef, internally chosen. Nominally, I would expect that to be 3.3 volts, but since it uses 5 volts as a power supply, that may not be right.

Can anybody enlighten me on this subject?

Thanks in. advance for any insights.

jrdoner

[missdrew]

Can anybody enlighten me on this subject?

Probably a better question for SeeedStudio. While the board CAN be programmed by the Arduino IDE, the manufacturer wrote the plugin, and know the specifications very well.

[missdrew]

Found in 'wiring_analog.h'. Only tried AR_INTERNAL1V1, it does compile.

typedef enum _eAnalogReference
{
AR_DEFAULT,
AR_INTERNAL1V0,
AR_INTERNAL1V1,
AR_INTERNAL1V2,
AR_INTERNAL1V25,
AR_INTERNAL2V0,
AR_INTERNAL2V2,
AR_INTERNAL2V23,
AR_INTERNAL2V4,
AR_INTERNAL2V5,
AR_INTERNAL1V65,
AR_EXTERNAL
} eAnalogReference ;

[jrdoner]

Thanks for the data. Oddly enough, when I use AR_INTERNAL2V5, I find I must use 3.14, not 2.5, as the reference voltage. It seems to be impossible to locate any detailed information of the accuracy and full range of the XIAO's ADC process.

[uxomm]

My experience with Seeeduino XIAO and AnalogReference is:
only 4 settings are working:

analogReference(AR_DEFAULT);    // 3.3 V
analogReference(AR_INTERNAL1V0);
analogReference(AR_INTERNAL2V23);
analogReference(AR_INTERNAL1V65);

All others will be treated like "AR_DEFAULT": 3.3 V

General experience with XIAO and analogRead: it is not too accurate.
So if you need accurate readings you may look for an external ADC.