1. SENSORS
ThinkLABS
www.thinklabs.in

2. SENSORS
 Capability and Complexity of any robotic system is
directly dependent on its number of sensory
inputs
www.thinklabs.in

3. SENSOR: THE FAMILY
Sensors
Proximity/ Range Environmental
Mechanical Reflective Light
Tactile
Infrared Temperature
Switches
Visible Light Pressure
Ultrasound Humidity
Gases

4. PROXIMITY: TACTILE SWITCHES
 Mechanical Switches
(limit switches) to
detect the presence or
absence of an obstacle
 Most reliable and
widely available
 Simple to use
www.thinklabs.in

5. PROXIMITY: INFRARED
 Sensors working in the
infrared region
 Invisible to human eye
 Detectable by digital
cameras
 Widely used in non-
contact proximity
sensing
 780nm to 1300nm
www.thinklabs.in

6. PROXIMITY: IR REFLECTIVE
Obstacle
 Infrared LED paired with
an infrared photodiode or
phototransistor
 Based on the property of
reflection
 Measuring the intensity of IR IR
the reflected signal LED Detector
www.thinklabs.in

7. PROXIMITY: IR LED
 Transmits infrared light
 Available in different
shapes and sizes
 Categorized according to
output wavelength and
power
[ TV remote viewed through a digi-cam]
 Can be hacked from old
computer mice or remote
controls
www.thinklabs.in

8. EXPERIMENTS: IR LED
R1 = 100, 150, 620
www.thinklabs.in

9. PROXIMITY : IR PHOTODIODE
 Used in either zero bias or
reverse bias mode
 In zero bias it acts like a
solar cell
 In reverse bias, its
resistance changes with
the change in intensity of
incident light
www.thinklabs.in

10. IR PHOTODIODE
 IR Photodiode Spectral Responsivity
www.thinklabs.in

11. EXPERIMENTS: Photodiode
R1 could be anywhere between
4.7K to 10K
Photodiode in reverse biased condition
www.thinklabs.in

12. EXPERIMENTS: Photodiode
Photodiode in reverse biased condition
www.thinklabs.in

13. PROXIMITY : IR PHOTOTRANSISTOR
 Similar to a transparent
BJT without the base
terminal
 Much more sensitive than
an IR photodiode due to
internal amplification
 Slower response
www.thinklabs.in

14. EXPERIMENTS: IR Pair
www.thinklabs.in

15. PROXIMITY: ULTRASONIC
 Using sound frequencies
above 25Khz
 Based on the principle of
echo
 Calculation of time of
flight, phase change and
attenuation of received
signal [ Ultrasonic transducer pair ]
 Highly accurate
 Slow response
www.thinklabs.in

16. SENSORS: ENVIRONMENTAL
 Light
 Temperature
 Pressure
 Humidity
 Gases
www.thinklabs.in

17. ENVIRONMENTAL: LIGHT
 Light Dependent Resistor
(LDR)
 Made up of Cadmium
Sulphide (Cds)
 Range: 200 Ohms in light
to 2M Ohms in darkness
 Sensitive to the whole
spectrum of light
 Cheap and easy to use
www.thinklabs.in

18. ENVIRONMENTAL: TEMPERATURE
 Thermistors
 Resistance changes with
the change in temperature
 Types: PTC & NTC
www.thinklabs.in

19. LDR CIRCUIT
LDR min value < R1 < LDR max value
R1 value should be close to the mean
of Max and Min values of the LDR
LDR in a potential divider
www.thinklabs.in

20. ANY QUESTIONS?
www.thinklabs.in