Path Following Robot with Obstacle Detection

The main aim of this project is to design a robot that can follow a black path without collisions detect the end of the path and turn back. The black path below the car can be determined using the principle that black color absorbs all radiations and the presence of an obstacle is detected using ultrasonic waves.

The project comprises of four main blocks

Infrared Transmitter and Receiver

IR transmitter consists of a IR led while the receiver used is IR transistors L14G2. When the Infrared rays fall over base of the IR Led, it is turned on. To catch this variation, the collector of IR transistor is fed to a comparators in LM324 IC  as shown in the circuit diagram. We use 4 such Tx Rx modules each at the corner of a rectangle. When the robot reaches the end of the path, only the forward Tx Rx detect white path while the backward Tx Rx module still detect the black path. This case is used to turn around the robot until the forward Tx Rx modules detect black path. In other cases, the robot turns left if one/both of the right Tx Rx module detect a white path. Similarly, the robot turns right if one/both of the left Tx Rx module detect white path. If all of the Tx Rx module detect a black path the robot moves forward.

Black Line Detection Circuit

Ultrasonic Transmitter and Receiver

Ultrasonic signals are used to detect obstacles in the path of the robot. Ultrasonic signals scores over Infrared signals in that they can detect obstacles of irregular shape as well as that of black color. Complete design of the circuit can be found here :  Ultrasonic Transmitter and Receiver

Microcontroller

The  microcontroller used here is 89c51. It is interfaced with DC motor driver H-Bridge IC L293D. The pins P0.0 to P0.3 receive the 4 IR signals indicating weather they are on black or white path. The microcontroller is programmed to drive the robot in either forward, left or right direction. The   microcontroller also continuously monitors the pin P0.4 which is connected to the output of ultrasonic obstacle detection circuit. When the pin P0.4 detects a obstacle, the microcontroller stops the robot. On reaching the end of the path, the microntroller rotates the robot until it encounters the black path and then continues foward. 




Microcontroller interface to H-Bridge

H-Bridge and DC motors

The robot is driven by DC motors. To drive the motors we use an H-bridge-L293d which boosts the microcontroller logic voltage to 9v that is required to drive these motors. In our case, we used a 9v, 100rpm DC motor. To achieve higher speeds, DC motors of higher torque and voltage can be used.