Photoresistor Notes
Choosing an optimal resistor for photoresistor voltage divider-
http://www.buildcircuit.com/voltage-divider-rule/
The value of the resistor R will determine the range of the output Voltage Vo. For best results you need a large ‘swing’ (range) for Vo and this is achieved if the resistor is much larger than the sensor’s minimum resistance Rmin, but much smaller than the sensor’s maximum resistance Rmax.
You can use a multimeter to help you find the minimum and maximum values of the sensor’s resistance (Rmin and Rmax). There is no need to be precise, approximate values will do.
Then choose resistor value: R = square root of (Rmin × Rmax)
Choose a standard value which is close to this calculated value.
For example:
An LDR: Rmin = 100R, Rmax = 1M, so R = square root of (100 × 1M) = 10K.
For more information, see "Reading a Photocell" at https://learn.adafruit.com/photocells/using-a-photocell
http://www.buildcircuit.com/voltage-divider-rule/
The value of the resistor R will determine the range of the output Voltage Vo. For best results you need a large ‘swing’ (range) for Vo and this is achieved if the resistor is much larger than the sensor’s minimum resistance Rmin, but much smaller than the sensor’s maximum resistance Rmax.
You can use a multimeter to help you find the minimum and maximum values of the sensor’s resistance (Rmin and Rmax). There is no need to be precise, approximate values will do.
Then choose resistor value: R = square root of (Rmin × Rmax)
Choose a standard value which is close to this calculated value.
For example:
An LDR: Rmin = 100R, Rmax = 1M, so R = square root of (100 × 1M) = 10K.
For more information, see "Reading a Photocell" at https://learn.adafruit.com/photocells/using-a-photocell