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Energia with TM4C123 battery monitoring ADC problem

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Hello,

 

I am trying to measure voltage across a voltage diviter with a Tiva-C series boards, and I am consistently getting mis results.

 

I get 0-4096 for 0 to 3.3V. I also have a seperate battery, that goes in to a 100K + 15K voltage divider network and PE_2 is connected to the middle of the voltage divider.

 

It measures 1.1V approximately, when it should be measuring 0.77V. But here is the interesting part. When I use a multimeter to measure the same middle point in the voltage divider, it reads 0.77, and the value from the analog read also converges to 0.77 - then i disconnect the multimeter it will go up to 1.1V back.

 

This brings the question: what is the analog state of this adc pin? does it has to be initialized with pinMode as input, in order to do analogRead?

 

Best regards,

C.A.


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