PIC16F877 and voltage measurment on LED

[tomas]

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

 

[betwixt]

If your -Ve reference is VSS (it usually is) and the bottom of the LED is connected to VSS, connect the analog pin to the junction of the LED and resistor.

Brian.

 

[tpetar]

Like Betwixt says connect ADC pin on LED anode (between led and resistor). Gnd is common.


You can see this existing EDABoard thread:

https://www.edaboard.com/threads/196948/



Also look this simple 3-digit LED voltmeter:

https://www.coolcircuit.com/project/meter/

 

[tomas]

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

 

[tpetar]

Yes my friend make it common (connect both Gnd together).

 

[betwixt]

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.

 

[tomas]

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