0 - 10V input on PIC 16F876

[Robinzon Kruso]

Charles hit the nail on the head.

0-10v input  ----------+
                       |
                      _|_
                      | |
                      |R|
                      |_|
                       |
                       |
                       +--------- PIC ADC Input (0-5v)
                       |          |
                      _|_         |
                      | |        __
                      |R|         /  5V
                      |_|        /\
                       |         --
                       |          |
                       | ________ |
                     Ground

You should make sure that more than five volts not to be loaded to microcontrollers pin otherwise it could become foul. For example if for any case you have more than 10V as an input you will get more than 5V on the resistor and on PIC as well, so it is not bed to think about some zener diode on PIC ADC input. Or maybe is better to use a scheme with comparator LM239 which will sharply cut any voltage bigger than Vcc ref+ loaded on pin 6 of LM239.

Regards

[slayerizer]

ah, yes, I see.... if the voltage over the pin exceeds 5 V, the zener will pull the pin to 0...
it is yet a prototype, but when I make a final design, I should probably add it for safety...
thanks...
I think my prototype is ready for testing, Thanks all

[Dave]

slayerizer, The zener does not pull the pin to 0 volts but, starts to conduct at the breakover voltage it is designed for. It will then maintain that voltage as long as the power of the component is not exceeded. In other word it is acting as a limiter....

Dave Purola,
N8NTA

[Ioannis]

...

In other word it is acting as a limiter....

Yes but not like a switch! It is like a normal diode in characteristics slightly steeper. But has a knee. That means if voltage is increasing above about 4,3Volts the zener might start to conduct and spoil the readings of the ADC.

I may have not stated correctly in engineering terms. If anyone with native english understood, please help here.

Ioannis