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IR Sensor for Line Follower
Characteristic of IR sensor
- The emitter transmits IR light
- The receiver receives the reflected IR light
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.
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.
IR Sensor for Line Follower
IR sensor circuit used in CEG3430 robot
-Modulated IR sensor circuit avoid interference by the ambient light.
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
S1
IR Emitter
S2
v1
v1<v2 -> low
+
v2
Comparator
IR Sensor for Line Follower
Differential IR sensor circuit proposed by Prof.
K.H. Lee
-
Advantages of using differential IR sensor circuit :
(1) Independent of ambient light.
(2) Independent of floor material and color.
(3) Avoid interference by fluctuation of light condition in
surrounding environment. Such as camera flash etc.
(4) More reliable.
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
v1+0.6
+
If v2-v1 > 0.6 volt
then output -> low
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
v1+1.2
+
If v2-v1 > 0.6 volt
then output -> low
IR Sensor for Line Follower
Implementation of Differential IR sensor circuit.
-
The actual implemented circuit is as follow:
VCC
VCC
2K
10K
s1
s2
Comparator
v1=v2-0.6
0.6 volt
VCC
10K
LM339_1
+
VCC
10K
1N4148
Out
v2=v1+0.6
D1
D2
0.6 volt
LM339_2
D3
v1+1.2
+
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.
IR Sensor for Line Follower
Differential IR sensor module circuit diagram.
IR Sensor for Line Follower
References
-
Diode 1N4148 datasheet:
http://download.siliconexpert.com/pdfs/diode/hit/e208147_1
n4148.pdf
-
Comparator LM339 data sheet:
http://www.onsemi.com/pub/Collateral/LM339-D.PDF
-
OR gate 74LS32 data sheet:
http://ece-www.colorado.edu/~mcclurel/dm74ls32.pdf