I am trying to use PDV-P8103 photocell as a sensor for LCD dimming circuit. The application requirements are to have comfortable brightness level from almost total darkness up to direct sunlight.
The problem is that the cell swings between about 300 Ohm all the way to over 1M. Usual connection as part of voltage divider simply does not work, as depending on fixed resistor the ADC quickly saturates at either 0 or VCC.
Is there a simple way to squeeze dynamic range of a photocell into something useful for reading by ADC? Note, that the precision is not important for this application, only the ballpark ambient light assessment.
Here are some approaches I have considered:
Adding OP-Amp in attenuator configuration;
Powering the voltage divider from DAC output and use it to select range first before sampling ADC;
Giving up on full range and picking fixed resistor for dark conditions, since human eyes adapt to darkness much better than to bright light.
Neither of the above struck me as ideal solution, so any ideas are welcome.