Lesson 12 Photo-interrupter

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Introduction

A photo-interrupter (as shown below) is a sensor with a light-emitting component and light-receiving component packaged and placed on face-to-face. It applies the principle that light is interrupted when an object passes through the sensor. Therefore, photo-interrupters are widely used in speed measurement.

Required Components

– 1 * Raspberry Pi

– 1 * Breadboard

– 1 * Dual-color LED module

– 1 * Photo-interrupter module

– 2 * 3-Pin anti-reverse cable

Experimental Principle

Basically a photo-interrupter consists of two parts: transmitter and receiver. The transmitter (e.g., an LED or a laser) emits light and then the light goes to the receiver. If that light beam between the transmitter and receiver is interrupted by an obstacle, the receiver will detect no incident light even for a moment and the output level will change. In this experiment, we will turn an LED on or off by using this change. The schematic diagram:

Experimental Procedures

Step 1: Build the circuit.

Raspberry Pi	GPIO Extension Board	Photo-interrupter Module
GPIO0	GPIO17	SIG
3.3V	3V3	VCC
GND	GND	GND

Raspberry Pi	GPIO Extension Board	Dual-color LED Module
GPIO1	GPIO18	R
GND	GND	GND
GPIO2	GPIO27	G

For C Users:

Step 2: Change directory.

    cd /home/pi/SunFounder_SensorKit_for_RPi2/C/12_photo_interrupter/

Step 3: Compile.

    gcc photo_interrupter.c -lwiringPi

Step 4: Run.

    sudo ./a.out

For Python Users:

Step 2: Change directory.

    cd /home/pi/SunFounder_SensorKit_for_RPi2/Python/

Step 3: Run.

    sudo python3 12_photo_interrupter.py

Now the LED will light up green. Stick a piece of paper in the gap of photo interrupter. Then “Light was blocked” will be printed on the screen and the LED will flash red. Remove the paper, and the LED will turn green again.