Block Diagram
The robot uses IR sensors tosense the line, an array of 8 IR LEDs(Tx) and sensors (Rx), facing the ground has beenused in this setup. The output of the sensors is an analog signal which dependson the amount of light reflected back, this analog signal is given to the comparatorto produce 0s and 1s which are then fed to the µC.
| L4 | L3 | L2 | L1 | R1 | R2 | R3 | R4 |
Left Center Right
Sensor Array
Starting from the center, thesensors on the left are named L1, L2, L3, L4 and those on the right are namedR1, R2, R3, R4.
Let us assume that when a sensor is on the line it reads 0 and when it is off the line it reads1
The µC decides the next move soas to position the robot such that L1 and R1 both read 0 and the rest read 1.
| L4 | L3 | L2 | L1 | R1 | R2 | R3 | R4 |
| 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 |
Left Center Right
Desired State L1=R1=0, and Rest=1
Algorithm:
1. L= leftmost sensor which reads 0; R= rightmost sensor whichreads 0.
If no sensor on Left (or Right) is 0 then L (or R) equals0;
For example:
| L4 | L3 | L2 | L1 | R1 | R2 | R3 | R4 |
| 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |
Left Center Right
Here L=3 R=0
| L4 | L3 | L2 | L1 | R1 | R2 | R3 | R4 |
| 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
Left Center Right
Here L=2 R=4
2. If all sensors read 1 go to step 3,
else,
IfL>R Move Left
If L<R Move Right
If L=R Move Forward
Go to step 4
3. Move Clockwise if line was lastseen on Right
Move Counter Clockwiseif line was last seen on Left
Repeat step 3 till line is found.
4. Go to step 1.
Sensor Circuit
Fora good voltage swing from the potential divider use
R1=Sqrt (Resistance of sensor when light falls on it *
Resistanceof sensor when light does not fall on it)
Motor Interface andControl Circuit:
The 8 sensors are connected to PORTA.
You need not connect anythingto AVCC and AREF,
it is required only if ADC is used.
The L298 Motor Driver has 4 inputs to control themotion
of the motors and two enable inputs which are used for
switching themotors on and off. To control the speed of the motors a
PWM waveform withvariable duty cycle is applied to the enable pins.
Rapidly switching thevoltage between Vs and GND gives an effective
voltage between Vs and GND whosevalue depends on the duty cycle
of PWM. 100% duty cycle corresponds to voltageequal to Vs, 50 %
of the motors from disturbing the remaining circuit.
Download:
Source code: Lfsource.c
Complete Document: AVR Line Follwing Robot