Here are Some hardware question following schematic and specification.
Vbat range: "AA or AAA''. What are the high and low limits for voltage range? ( destruction for high and SAMD21 behaviour for low)
Analog input: Could you confirm that internal ADC Is referenced to AVREF. If we plan to use it, do we need to connect it to external ref ? 3V3 could be used?
Schematic: I open eagle design files and I don't understand why Vbatt has two net names : VBATT/2.5A and VBATT/1.4C. In schematic I understand they are not connected. In layout I see they are connected. Thus PB08_AIN3 is used to monitor battery with resistor voltage factor = 33/(68+33)=0.326
To use this input for battery voltage monitorg, do we need to use code :
analogRead(ADC_BATTERY) or analogRead(A3)
and performed scaling conversion ( Vref= ? ; 1024bit ; 0.326 ratio see above)
Hi, the uppper limit is 3V while the lower limit is more or less 1.8V since the D21 stops working under this voltage.
The voltage divider is designed in such a way you can use the 1.0V bandgap voltage reference so you should use
analogReference(AR_INTERNAL1V0) before making the analogRead(ADC_BATTERY)
Thank for your helps. Here is ma solution :
I add the 1.032 due to real measurement, for compensation. As explained in datasheet
SAM D21E / SAM D21G / SAM D21J chapter 44.6.3 : The 1V internal reference is not high precision. For precision use ratiometric reference or external ref.
For max voltage range I read in 8.2.1 : 1.62V to 3.63V. Need more reading in datasheet. 3.8v is the destructive value.
we need to check also the sigfox module limitation and datasheet.