ЁЯдЦ

Introduction to IR Sensor and Wiring

Sep 16, 2025

Procedure: Construction and Testing of an Infrared (IR) Sensor Circuit

This procedure outlines the step-by-step assembly and testing of an IR sensor circuit, detailing the connections and orientation of each component.

1. Preparation of Components

  • Gather the following components:
    • 1 IR LED (transmitter)
    • 1 photodiode (receiver)
    • 2 resistors (330 ╬й each)
    • 1 standard LED (for indication)
    • Connecting wires
    • 9V battery (or suitable power supply)

2. Identifying Terminals

  • IR LED:
    • The positive terminal is typically the longer leg or the side with a smaller internal area.
    • The negative terminal is the shorter leg or the side with a larger internal area.
  • Photodiode:
    • The negative terminal is identified by the flat side at the base of the photodiode.
    • The positive terminal is the opposite leg.

3. Connecting the IR LED (Transmitter)

  • Connect the positive terminal of the IR LED to the positive terminal (VCC) of the 9V battery.
  • Connect the negative terminal of the IR LED to one end of a 330 ╬й resistor.
  • Connect the other end of this resistor to the ground (negative terminal) of the battery.
  • Once powered, the IR LED will emit infrared rays. These rays are not visible to the naked eye but can be seen as a faint purple glow through a camera.

4. Connecting the Photodiode (Receiver) and Indicator LED

  • Connect the negative terminal (flat side) of the photodiode to the positive terminal (VCC) of the battery.
  • Connect the positive terminal of the photodiode to one end of the second 330 ╬й resistor.
  • Connect the other end of this resistor to ground (negative terminal of the battery).
  • At the junction between the photodiode and the resistor, connect the anode (positive leg) of the standard LED.
  • Connect the cathode (negative leg) of the standard LED to ground. If necessary, add an additional resistor in series with the LED to limit current and prevent damage.

5. Powering the Circuit

  • Connect the positive terminal of the 9V battery to the VCC lines of both the IR LED and the photodiode circuits.
  • Connect the negative terminal of the battery to the ground lines of both circuits.
  • Ensure all connections are secure and that there are no short circuits.

6. Alignment and Testing

  • Position the IR LED and the photodiode so that they face each other directly. Adjust their angles to ensure the IR rays from the LED can reach the photodiode.
  • Power on the circuit by connecting the battery.
  • Observe the indicator LED:
    • If the IR LED and photodiode are properly aligned, the indicator LED will glow, indicating that the photodiode is receiving IR rays.
    • If the indicator LED does not glow, adjust the alignment of the IR LED and photodiode until the LED lights up.
  • To test the sensorтАЩs response, place an obstacle (such as a piece of cardboard) between the IR LED and the photodiode:
    • The indicator LED should dim or turn off, showing that the IR rays are blocked.
    • Remove the obstacle; the indicator LED should glow again.
  • Note: Ambient light, especially daylight, may cause the photodiode to conduct slightly, so the indicator LED may glow faintly even without direct IR LED transmission.

7. Additional Observations

  • If the IR LEDтАЩs legs are trimmed and difficult to distinguish, identify the terminals by examining the internal structure: the larger internal area is negative, and the smaller area is positive.
  • For the photodiode, if the internal structure is not visible, use the flat side at the base to identify the negative terminal.
  • The IR LED should always be connected in forward bias (positive to VCC, negative to ground through a resistor).
  • The photodiode should always be connected in reverse bias (negative to VCC, positive to ground through a resistor).

8. Application Note

  • This basic IR sensor circuit demonstrates the principle of wireless detection using infrared light.
  • The same configuration is used in applications such as line follower robots, where a pair of IR LED and photodiode is used for path detection.
  • In advanced circuits, operational amplifiers may be added for signal processing and decision-making, but the fundamental connections remain the same.

By following this procedure, the IR sensor circuit can be constructed and tested to demonstrate the detection of infrared rays and the effect of obstacles on signal transmission. Proper identification of terminals and careful alignment of the transmitter and receiver are essential for successful operation.

Full transcript