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Monitoring battery voltage

Mohammad Mohiuddin
Prodigy 230 points

I am using F2350 µC.

Power for the µC will come from CR2032 battery. To monitor this battery’s voltage level, I can use internal reference voltages (1.8V or 2.5V) and some firmware. No additional component is needed. Correct?

 

There is another battery in this system. The starting voltage for that battery will be 1.5V (single AA cell). How can this voltage be monitored? Any reference design.

Can this battery be connected to CA0 (pin 15) and internal voltage reference be used also?

Thanks,

  • 0
    Guru 227245 points

    Mohammad Mohiuddin said:
    Power for the µC will come from CR2032 battery. To monitor this battery’s voltage level, I can use internal reference voltages (1.8V or 2.5V) and some firmware. No additional component is needed. Correct?

    Yes. The ADCs haev an internal input channel that measures VCC/2 against a reference voltage. Of course it makes no sense to measure against VCC as reference. So 2.5V reference is needed (and consumes energy while active). 1.5V reference is not recommended here since the input voltage is near 3V. YOu wouldn't be able to detect a battery voltage above 3V with 1.5V reference. (se ebelow)

    Mohammad Mohiuddin said:
    The starting voltage for that battery will be 1.5V (single AA cell). How can this voltage be monitored?

    Simply connect it to anotehr external analog input and convert it against any reference you like. You may even check it against VCC, once you have measured VCC against 2.5V and know its value. So if your VCC check happens less often than teh rest, thsi allows you to keep the reference off for the 'normal' conversions.

    However...

    Mohammad Mohiuddin said:
    I am using F2350 µC.

    Thsi one neither has an ADC nor does it have any reference voltages. The comparator it has can only compare against 1/4 VCC or 1/2 VCC or roughly 0.5V. So it is not suitable to check VCC itself. Or to get any absolute voltage.

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