# Help with 16F876

Discussion in '8bit Microcontrollers' started by CJunk, Jun 1, 2004.

1. ### CJunkGuest

Hi there. Just was wondering if anyone can lead me to a site or give me
info that will show me basic operation of the ADC in the PIC16F876. I have
tried getting it to work but cannot seem to do it. I have checked out
www.microchip.com and the info there but it dont help me. Would like a
simple schematic and software guide if possible.thx

2. ### CJunkGuest

Dont worry I figured it out.

thx

3. ### davidGuest

was it a simple mistake why tell us how you fixed so quickly it might help
someone else.
David

4. ### CJunkGuest

ok.... Initially I was connecting the 5k pot to the analogue input (RA0),
but didnt put the connection to the center of it and + to the one pot pin
and Gnd to other pot pin. I was just using two of the pins on the pot. I
hope what I typed came out all right. ...and hopefully it will help some
beginners out there.

5. ### Howard LongGuest

The other 'gotha' I've encountered on the 16F876 ADC is the relatively low
impedance of the ADC input.

Kind Regards, Howard

6. ### CJunkGuest

Could you please let me know what 'impedance' affects? thx

7. ### Eric BohlmanGuest

It means that the ADC will draw a non-trivial amount of current from the
source of the voltage that it's measuring. If the voltage source has a
high impedance, then drawing too much current from it will actually lower
the voltage it's supplying, and the reading will be wrong.

Consider a hypothetical ADC input with an input impedance of 5K. If you
were to connect it directly to a 5-volt supply, you'd accurately read 5
volts. But now consider connecting it to the 5-volt supply through a 1K
resistor. You'd read only 4.17 volts, because the impedance of the ADC
input forms a voltage divider with the resistor. If, OTOH, the input
impedance were 50K, you'd read 4.9 volts; you'd still have a voltage
divider, but the drop across the source resistor would be much smaller.

8. ### Howard LongGuest

.... I think that about covers it!

Regards, Howard

9. ### CJunkGuest

thx

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