Photocell Sensor

Basic Photocell Sensor Circuit

What is a photocell sensor?

Photocell sensor can be regarded as a transducer that is used to detect the light intensity. At full intensity beam with a photocell resistance could be worth about 10 Ohm and the low intensity light (in darkness) could be worth several hundred Ohm.

Photocell Light Sensor

A photocell sensor resistance value varies between the two terminals based on the number of photons (light) it receives. Electronic application that uses a photocell sensor as a light sensor, such as  overcast (rain) sensor, auto-afternoon street lamps, photographic light meters, and other applications that are sensitive to light.

Semiconductor material used to manufacture  photocell usually use cadmium sulfide (Cds) in addition to other additional elements. Included in photocell sensor family of Light Dependent Resistor (LDR) and Photoresistor. Photocells and diodes are used for similar applications, but the photocell through bi-directional flow, while the diode is a one-way. When the photocell receives more photons, reducing the resistance between two terminals.

Basic Photocell Sensor Circuit

Here is the basic photocell detector circuit using a Cadmium Sulfide (Cds) photocell sensor. The workings of this photocell sensor circuit, when the light falling on the photocell (PC1) is blocked, the resistance will increase and the voltage on the PC1 will rise. When the voltage rises above half of the supply voltage, the output of the comparator will turn on and the LED will light.

Basic Photocell Sensor Circuit Schematic

Because of wide variation in CdS photocells is usually best to install the cell and then measure the resistance under normal lighting conditions. A resistor with a value of approximately three to five times the cell resistance measured is then selected for R1. For example, if the cell resistance was measured at 400 ohms then from 1200 to 2200 ohm resistor is used.

Increasing the value of R1 will cause the sensitivity of the photocell sensor decreases. This may be required when the light that falls on these cells is not too strong or shadows can affect the photocell.

This photocell detector circuit can be adapted for use in dark areas by placing a small light on the photocell. For external use, you can use the an outdoor photocell sensor, in this basic circuit used 12 volt photocell sensor.

Read more: Auto Battery Charger Circuit-LM338 Power Supply Circuit