Created on: 3 January 2018
Pinout of the photo resistor sensor module from the 37 in 1 sensor kit for Arduino from Geekcreit, Elegoo, Elektor and others. A photo resistor is also known as a Light Dependent Resistor (LDR) or photocell. Although the kit describes it as a "photo resistor", it is more commonly written "photoresistor" or "photo-resistor".
The photo resistor module detects light intensity. As the intensity of light on the photoresistor increases, so the resistance of the photoresistor decreases. A built in 10k resistor on the module can be used to build a divider circuit for measuring changes in light intensity from the photoresistor. A device such as an Arduino can be used to read the light intensity using and analog input pin.
This photo resistor module is found in the 37 in 1 sensor kit that is branded under several different names and found in many online shops.
To find out more about photoresistors, see the photoresistor Wikipedia article.
There are two different configurations for this module, depending on which kit they come from. The difference is which pins the 10k resistor is connected to on the module.
Before continuing, check your module with a multimeter to make sure which configuration your module is using. Both configurations are shown in the pinout images below.
Note one difference in the below images of the module – on the first module, the text R1 is silk-screened to the left of the board and is upside down. In the second image, R1 is silk-screened at the right of the board.
The image below shows the pinout for the Geekcreit photo resistor sensor module. The photoresistor connects between the outer two pins of the module. A 10k resistor connects from the middle pin to the right pin as can be seen in the circuit diagram of the module at the right of the image.
It is suggested to use a multimeter to check whether this is the configuration of your module, or if your module uses the configuration in the next pinout image below.
In the image below, an alternate configuration of the photo resistor sensor module can be seen. The 10k resistor connects between the middle pin and the left pin of the module.
Resistance of the photoresistor is typically less than 80 Ohms (< 80Ω) in full light.
Dark resistance is typically greater than 20 Meg Ohms (> 20MΩ) – when the photoresistor is in full darkness.
The photo resistor module tutorial shows basic use and testing of the photo resistor module with Arduino.