Lights and Display Board Circuits

PHOTOTRANSISTOR-BASED LIGHT-SENSITIVE SCHEMATIC CIRCUIT DIAGRAM

A Phototransistor-Based Light-Sensitive Circuit is a circuit that uses a phototransistor to detect light levels and produce an output voltage or current based on the intensity of the light. Phototransistors are light-sensitive transistors that can be used as sensors in various applications, such as light meters, automatic streetlights, and optical communication systems. Here’s a description of the components and their functions in the schematic circuit diagram of a basic phototransistor-based light-sensitive circuit:

Phototransistor:

  • It is the key component in this circuit. It acts as a light sensor. When exposed to light, the phototransistor conducts, allowing current to flow between its collector and emitter terminals. The amount of current flowing through the phototransistor is directly proportional to the intensity of the incident light.

Resistor (Biasing Resistor):

  • A resistor is connected in series with the phototransistor to bias it properly. The value of this resistor is chosen based on the specifications of the phototransistor and the desired operating conditions.

Load Resistor:

  • A load resistor is connected in series with the collector of the phototransistor. The voltage across this resistor is used as the output signal. The value of the load resistor determines the output voltage or current based on the current flowing through the phototransistor.

Power Supply:

  • Provides the necessary power to the circuit. The power supply voltage should be compatible with the specifications of the phototransistor.

Output:

  • The voltage across the load resistor serves as the output signal of the circuit. This signal can be further processed or used to drive other electronic components based on the light level detected by the phototransistor.

PHOTOTRANSISTOR-BASED LIGHT-SENSITIVE SCHEMATIC CIRCUIT DIAGRAM

In this circuit, when activated, the component passes current through the conduction transistor BC547. When BC547 conducts, it triggers the relay, illuminating the lamp. When the light on the phototransistor is blocked, the relay returns to its initial state. The desired illumination intensity can be adjusted using the R1 potentiometer. As evident, the circuit is sensitive to daylight. To make it specifically responsive to infrared rays, the phototransistor’s lens needs to be covered with dark transparent plastic, allowing it to detect only the infrared rays emitted by the transceivers.

Consider setting up a room alarm. A mini infrared transceiver circuit is placed on one side of the room, while the circuit shown in figure 3.22 is installed on the opposite wall. When an object passes between the two circuits, the infrared rays received by the phototransistor are interrupted. This interruption causes the phototransistor to stop conducting through the BC547 transistor. The change in BC547’s state alters the relay contacts, turning off the lamp.

BC547, known for its affordability and ease of use, is often employed in designing low-cost water level indicators. It finds practical applications in everyday scenarios, such as detecting water levels in containers.

Additionally, BC547 serves as a versatile transistor for current amplification, rapid switching, and pulse-width modulation (PWM). Consequently, it is widely used in projects where precise control over motor speed or actuators is required.

BC547 Transistor Features

  • Bi-Polar NPN Transistor
  • DC Current Gain (hFE) is 800 maximum
  • Continuous Collector current (IC) is 100mA
  • Emitter Base Voltage (VBE) is 6V
  • Base Current(IB) is 5mA maximum
  • Available in To-92 Package

Applications

  • High Voltage: BC546, VCEO=65V
  • Low Noise: BC549, BC550
  • Complement to BC556 … BC560
Tags

Related Articles

Leave a Reply

Your email address will not be published.

Back to top button
Close
Close