This repository contains the circuit design and logic implementation for a Line-Following Robot built using 4 sensors, logic gates, and DC motors. The robot uses basic digital logic gates to determine motor speeds based on sensor input and follows a line efficiently.
This line-following robot utilizes:
- 4 QTR sensors to detect the position of the line.
- Logic gates (AND, OR, NOT) to process the sensor signals.
- Two DC motors controlled via an H-Bridge Motor Driver (L293D).
- Two 555 Timer ICs to generate PWM signals for motor speed control.
The logic gates are implemented using 74HC series ICs, and the robot adjusts motor speed dynamically to align itself with the line.
| Item | Quantity |
|---|---|
| 10 kΩ Potentiometer | 2 |
| Diodes (LN4148) | 4 |
| 74HC04 (NOT Gate IC) | 1 |
| 74HC32 (OR Gate IC) | 2 |
| 74HC11 (AND Gate IC) | 2 |
| DC Motors | 2 |
| L293D (H-Bridge Driver) | 1 |
| 5V Power Input (Or regulate from 12V) | 1 |
| 12V Power Input | 1 |
| 5 kΩ Resistor | 2 |
| 1 kΩ Resistor | 2 |
| 5 nF Capacitors | 2 |
| 100 nF Capacitors | 2 |
| 555 Timer ICs | 2 |
| Single Channel Cables | 1m |
The robot consists of two main sections:
-
Sensor Processing Unit:
- 4 QTR sensors detect line position and output binary signals (0 or 1).
- These sensor signals are fed into NOT gates (inverters), AND gates, and OR gates to implement the decision-making logic.
-
Motor Control Unit:
- Two 555 Timer ICs generate PWM signals to control the motor speeds:
- 33% PWM for slow speed.
- 66% PWM for medium speed.
- 100% PWM for full speed.
- The H-Bridge Motor Driver (L293D) controls the direction and speed of the motors based on the logic output.
- Two 555 Timer ICs generate PWM signals to control the motor speeds:
The robot's logic is designed based on the following truth table:
| S1 | S2 | S3 | S4 | Left Motor | Right Motor | Explanation |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0% | 0% | No input - robot stops |
| 0 | 1 | 1 | 0 | 100% | 100% | Robot moves forward straight |
| 0 | 0 | 1 | 0 | 100% | 66% | Robot adjusts slightly to the right |
| 0 | 1 | 0 | 0 | 66% | 100% | Robot adjusts slightly to the left |
| 0 | 0 | 1 | 1 | 100% | 33% | Robot turns slowly to the left |
| 1 | 1 | 0 | 0 | 33% | 100% | Robot turns slowly to the left |
| 1 | 1 | 1 | 0 | 0% | 100% | Robot turns sharply left |
| 0 | 1 | 1 | 1 | 100% | 0% | Robot turns sharply right |
| 1 | 0 | 0 | 0 | 0% | 100% | Robot turns sharply left |
| 0 | 0 | 0 | 1 | 100% | 0% | Robot turns sharply right |
| 1 | 1 | 1 | 1 | 0% | 0% | Robot stops |
| 1 | 0 | 0 | 1 | 100% | 100% | Robot moves forward straight |
| 1 | 0 | 1 | 0 | 100% | 100% | Robot moves forward straight |
| 0 | 1 | 0 | 1 | 100% | 100% | Robot moves forward straight |
| 1 | 1 | 0 | 1 | 100% | 100% | Robot moves forward straight |
| 1 | 0 | 1 | 1 | 100% | 100% | Robot moves forward straight |
-
Sensor Input:
- The 4 QTR sensors detect the black line and provide binary outputs.
- Sensor values are processed through logic gates to determine motor actions.
-
Logic Processing:
- 74HC04 ICs (NOT gates) invert signals where necessary.
- 74HC11 ICs (AND gates) and 74HC32 ICs (OR gates) combine inputs to produce control signals.
-
Motor Speed Control:
- Based on the truth table, the two 555 Timer ICs generate PWM signals at different duty cycles.
- These PWM signals adjust motor speeds to steer the robot and keep it aligned with the line.
-
Motor Driving:
- The L293D H-Bridge Driver receives the control signals and drives the motors in the desired direction with the appropriate speed.
-
Connect the 4 QTR sensors to the breadboard and configure them to detect the line.
-
Wire up the NOT gates (74HC04), AND gates (74HC11), and OR gates (74HC32) according to the truth table.
-
Implement the 555 Timer ICs to generate PWM signals for motor speed control.
-
Connect the L293D Motor Driver to the motors and integrate it with the PWM outputs.
-
Power the circuit with:
- 5V for logic gates and sensors.
- 12V for the motors.
-
Test the circuit:
- Adjust the potentiometers to fine-tune motor speeds.
- Verify the sensor logic and motor responses against the truth table.
- Power on the robot with the 5V and 12V power lines. You can use a regulator (like LM7805) or L298n's regulator.
- Place the robot on a line (black tape or track).
- The robot will:
- Adjust motor speeds based on sensor inputs.
- Follow the line smoothly using the predefined logic.
- No Microcontroller: This robot relies purely on logic gates and analog electronics.
- Dynamic Speed Control: Motors adjust speeds to correct alignment deviations with potantiometers.
- Modular Design: Easily customizable for additional sensors or motors.
- Add more sensors for better precision.
- Turning to the last direction with a flip-flop circuit to prevent crossing the line.
This project is licensed under the MIT License.