1. IR Sensor for Line Follower
Characteristic of IR sensor
- The emitter transmits IR light
- The receiver receives the reflected IR light

2. IR Sensor for Line Follower
Characteristic of IR sensor
- The current passing through the IR receiver is proportional to the IR light energy intensity received by it.

3. IR Sensor for Line Follower
IR sensor circuit used in CEG3430 robot
More intensity of reflected IR light received by sensor, more voltage drop across the resistor in series with sensor.
VR1 used to adjust the
sensitivity of sensor circuit.

4. IR Sensor for Line Follower
IR sensor circuit used in CEG3430 robot
Modulated IR sensor circuit avoid interference by the ambient light.

5. IR Sensor for Line Follower
Differential IR sensor circuit proposed by Prof. K.H. Lee
The basic idea of differential IR sensor circuit is to compare two adjacent IR sensors output value.
- Only the difference between adjacent sensors value is used to detect the line.
v1>v2 -> high
v1<v2 -> low
IR Emitter S2 v1 S1 + v2 -
Comparator

6. IR Sensor for Line Follower
Differential IR sensor circuit proposed by Prof. K.H. Lee
Advantages of using differential IR sensor circuit :
Independent of ambient light.
Independent of floor material and color.
Avoid interference by fluctuation of light condition in surrounding environment. Such as camera flash etc.
More reliable.

7. IR Sensor for Line Follower
Design of Differential IR sensor circuit
Define v =| v1-v2|.
If v > 0.6 volt then line is detected.
Else if v <= 0.6 volt then no line is detected.
Comparator v1 -
If v1-v2 > 0.6 volt
then output - > low
v2+0.6 + v2 -
If v2-v1 > 0.6 volt then output -> low
v1+0.6 +

8. IR Sensor for Line Follower
Design of Differential IR sensor circuit
To achieve the previous rules, we have to use two comparators. One for determine v1-v2 > 0.6 volt, another for determine v2-v1 > 0.6 volt.
The circuit can be further modified as follow:
Comparator v1 -
If v1-v2 > 0.6 volt
then output - > low
v2+0.6 +
v2+0.6 -
If v2-v1 > 0.6 volt then output -> low
v1+1.2 +

9. IR Sensor for Line Follower
Implementation of Differential IR sensor circuit.
The actual implemented circuit is as follow:
VCC
VCC 2K
10K
Comparator
VCC
v1=v2-0.6 s1
10K s2 -
0.6 volt
LM339_1 +
Out
1N4148
v2=v1+0.6
VCC D1 - D2
0.6 volt
10K
LM339_2 D3
v1+1.2 +

10. IR Sensor for Line Follower
Implementation of Differential IR sensor circuit.
Diode 1N4148 D1, D2 and D3 provide 1.2 volt voltage difference between S1 output and negative terminal of LM339_2 .
Initially, tune the 10K VR such that v1 < v2 by 0.6 volt (both s1 and s2 sensors are at the same condition).
The voltage value at different points of the comparator should be as shown in the figure.
Pull up resistors must be added at the outputs of LM339, because LM339 is an open collector output device.

11. IR Sensor for Line Follower
Differential IR sensor module circuit diagram.

12. IR Sensor for Line Follower
References
Diode 1N4148 datasheet:
Comparator LM339 data sheet:
OR gate 74LS32 data sheet: