I posted a treatise on the ADC input and references a month ago,
hopefully that will solve some problems. For mica's anyway.
Specific to the battery reading on mica ADC7, it is converting
a fixed 2.something value (not the ATMEGA internal ref which I believe
is not used at all), and is using the battery Vcc voltage
as a reference, so when the bat goes down, the ADC7 level goes up.
Could it be more confusing? Sure....but I think there is a conversion
formula in the Getting Started manuals someplace.
Since the ADC ref is the battery, any sensor that is powered from
the same battery will droop in sync (hopefully linearly) so you
shouldn't need to do any correction as the batteries die. You won't
be able to get a "real" voltage from any other ADC without doing a
reverse calculation based on the ADC7 value, but you can get constant
relative readings.
MS
#AUNG AUNG PHYO WAI# wrote:
Hi All,
I would like to confirm with all of you for converting ADC readings into
battery voltage.
From MPR datasheet, we have a formula to change from ADC readings to
voltage at ADC channel 7 for measuring battery voltage.
*Vout = Vref xADC_FS/ ADC_output*
Vref = 1.223 V
ADC_FS = 1024
ADC_output = reading from ADC channel 7.
Is this formula can be applicable to other ADC channel readings
(ADC0..ADC6)? Currently, I got some readings from new sensor type, and I
would like to change ADC output to voltage for calibration of sensors.
Thanks you very much.
*Regards,*
*Aung Aung Phyo Wai *
**
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