PIC16F877 and voltage measurment on LED

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tomas

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How can I measure voltage which is on LED with microcontroller? How should I connect analog pin?
 

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LED and resistor is from other circuit, which is seperate from microcontroller. Should I make this GND common?
 

The measurement taken by the PIC is of one voltage relative to the other so you have to measure across the LED using ground and the ADC input as the two connections.

A word of warning - make sure it is safe to connect the two grounds first. Although they are both called ground, a true connection to Earth may not be present in the power supply feeding the PIC or the LED so they could be at different voltages.

Brian.
 
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thank you all for your time and answers Im done with my project
 

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