I'm very confused about ADC. I do apologize if these questions sound silly. I use ATMEGA328P for ADC.
Why is the negative terminal required for ADC to take measurements, if the ADC pin is already negative by itself?
Why does the ADC only take measurements when resistance is present between the ground and the ADC input pin? If I remove the 1k resistor, then measurements no longer work, why doesn't ADC pick this up, unless a resistor is present?
- If I take the VCC and GND wire between my fingers in separate hands, and let the ADC wire 'float', I get a wave: (no photo-cell, just bare wires, GND in my left hand VCC in my right hand and ADC input floating in the air)
What is this wave representing? If I don't hold the VCC and GND, then the ADCH is just showing random output, so the wave doesn't occur by itself. My vref is set to AREF of 4v.
If I connect the ADC to an aluminium jar, I see what appears to be square wave, is that possible that I'm picking up some kind of signal from random device, like for example wifi chip? or not without op-amp?