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→Analog voltage reading method
The way this works is that as the resistance of the photocell decreases, the total resistance of the photocell and the pulldown resistor decreases from over 600KΩ to 10KΩ. That means that the current flowing through both resistors increases which in turn causes the voltage across the fixed 10KΩ resistor to increase. Its quite a trick!
The way this works is that as the resistance of the photocell decreases, the total resistance of the photocell and the pulldown resistor decreases from over 600KΩ to 10KΩ. That means that the current flowing through both resistors increases which in turn causes the voltage across the fixed 10KΩ resistor to increase. Its quite a trick!
Ambient light like... Ambient light (lux) Photocell resistance (Ω) LDR + R (Ω) Current thru LDR +R Voltage across R
Dim hallway 0.1 lux 600KΩ 610 KΩ 0.008 mA 0.1 V
Moonlit night 1 lux 70 KΩ 80 KΩ 0.07 mA 0.6 V
Dark room 10 lux 10 KΩ 20 KΩ 0.25 mA 2.5 V
Dark overcast day / Bright room 100 lux 1.5 KΩ 11.5 KΩ 0.43 mA 4.3 V
Overcast day 1000 lux 300 Ω 10.03 KΩ 0.5 mA 5V
Source: [http://www.ladyada.net/learn/sensors/cds.html cds]
Source: [http://www.ladyada.net/learn/sensors/cds.html cds]