Arduino Forum

Products => MKR Boards => MKRFOX1200 => Topic started by: remis on Jul 10, 2017, 10:41 am

Title: specification details, Battery monitoring
Post by: remis on Jul 10, 2017, 10:41 am
Dear support,

Here are Some hardware question following schematic and specification.
https://www.arduino.cc/en/Main.ArduinoBoardMKRFox1200
https://www.arduino.cc/en/uploads/Main/MKRFox1200-schematic.pdf

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

voltage monitor:
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)

Many Thank's
Title: Re: specification details, Battery monitoring
Post by: Arduino_Genuino on Jul 11, 2017, 11:15 am
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)
Title: Re: specification details, Battery monitoring
Post by: remis on Jul 11, 2017, 04:40 pm
Thank for your helps. Here is ma solution :
setup :
 analogReadResolution(12);
  analogReference(AR_INTERNAL1V0);
main :
canvalue=analogRead(ADC_BATTERY);
  Vf=(canvalue/4095.0)*(1/1.032)*(1.0/(33.0/(68.0+33.0)));

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.