The basic circuit that can be used to use Photo Transistors As Light Sensors can use the following simple circuit.
1. Basic Circuit With HIGH Logic When Detecting Light
With the configuration in the first image above the photo transistor is able to provide HIGH logic when receiving light emission. At the receiving light, the collector-emitter foot conductivity value will rise so that Vout gets a voltage source from Vcc through the photo emitter’s emitter legs so that Vout is HIGH logic and vice versa when not receiving light then the photo transistors OFF and Vout are connected to ground through RL so that LOW .
Then for the second configuration of figure 1 above. When the photo transistor receives light then the photo transistor conducts so TR1 does not get the base bias so TR1 OFF and Vout HIGH logic. Then when the photo transistor does not receive the light fed photo transistor OFF and base transistor TR1 gets forward biased so TR1 ON and Vout are connected to ground through TR1 so Vout LOGIK logic LOW.
2. Basic Circuits With LOW Logic When Detecting Light
From the first set of images above when the photo transistors receive the light then the photo transistor ON so that Vout is connected to the ground through the photo transistor so that Vout LOW logic and vice versa when not receive light then the photo transistor OFF and Vout connected to Vcc through RL so HIGH logic. Then for the second configuration of picture 2 above when photo transistor receive light then photo transistor conducts so TR1 gets base bias so TR1 ON and Vout are connected to ground by TR1 so that Vout is logged LOW.
Then when the photo transistor does not receive the light fed photo transistor OFF and base transistor TR1 does not get forward bias so TR1 OFF and Vout are connected to Vcc through RL so Vout is HIGH logic. If there is time and components can be tried Light Switch With Photo Transistor . Light switches can be made from several kinds of light sensors. The following series of light switches are made using a light sensor in the form of photo transistors.
This series of light switches or light-controlled switches is very simple, because it is made with 1 transistor, 1 photo transistor, 1 relay, 1 variable of resistor and diode. This series of light switches can work on voltages 6 – 12 VDC or DC voltage that match according to the relay used. To set the light reception sensitivity is adjusted with VR1. Circuit Light Switch With Photo Transistor can be used to control multiple lamps in parallel with power depending on the ability of the relay used
Light Switch Series With Photo Transistor above can be used to control the garden lights, street lights, or lights that want to be turned on at night only automatically.