Hi,
I have a 2.2uF cap and 330K resistor in parallel going into the A/D channel of the PIC at the emitter of a phototransistor.The Top part of the circuit is part of a light sensor. The PIC has a 10 bit A/D.
However I am not seeing a full scale of 0V to 2.8V. Note. Using VDD (3.3V) as VREF for A/D. I am seeing around 690mV.
Do i need to lower the resistor value as i think the impedance is greater than the 10K input impedance of the PIC A/D. Hence the holding cap can't sample for long enough. Also any A/D leakage current multiplied by the 330K may cause a voltage drop. Or do i try snd reduce the 2.2uF to a lower value.
I cant seem to upload a schematic at all.
I would be grateful for any help.
Thanks in advance.
I have a 2.2uF cap and 330K resistor in parallel going into the A/D channel of the PIC at the emitter of a phototransistor.The Top part of the circuit is part of a light sensor. The PIC has a 10 bit A/D.
However I am not seeing a full scale of 0V to 2.8V. Note. Using VDD (3.3V) as VREF for A/D. I am seeing around 690mV.
Do i need to lower the resistor value as i think the impedance is greater than the 10K input impedance of the PIC A/D. Hence the holding cap can't sample for long enough. Also any A/D leakage current multiplied by the 330K may cause a voltage drop. Or do i try snd reduce the 2.2uF to a lower value.
I cant seem to upload a schematic at all.
I would be grateful for any help.
Thanks in advance.