Can I not source my own ADC pullup??? Very confused, with pic

[iso9001]

So.....

I think I may have messed up. My intention was to use some external switches hooked to my ADC. I planned on sourcing the voltage to the pullups from other PIC PORTA pins so that when I wanted to sleep, I could kill the power going to the switches.

**broken link removed**

The issue I'm having is that when the pullup's/output is off the ADC reads 0 as it should. When the pullups are on, the ADC reads 5V constantly. However, I can tell the switches are working and are changing the voltage on the two wires, the ADC is just not seeing it.

Any ideas?

 

[iso9001]

Not shown of course is where the ADC0/1 go to external switches with their own resistors and then to ground.

 

[Mosaic]

Your issue is one of impedance and loading.

The port pins both source & sink. If u want to 'block' the 5VDC pull up effect of the port pins use a diode oriented to allow sinking and not sourcing. Flip the diode if u want to force the 5VDC pullup but have no effect when the port pin "pulls down".

Is your ADC vref set as Vdd?

What are the voltages on the ADC lines when pullup is on and your switched voltage is applied, is it 5VDC or some other voltage.