Basics of Sensors

A sensor is a device which is used to sense the surroundings of it & gives some useful information about it. This information is used based on our

requirement. An electronic sensor gives the information by giving some electronic signal. This information is used to perform a

given task which needs interaction with the surroundings.

What is a Sensor?

What does an electronic sensor do?

• An electronic Sensor takes the input from its surroundings(thermally, mechanically, luminously etc.) and converts that input in an electronic signal which can be processed more easily than the original input.

• Few electronic sensors are IR sensor, TSOP sensor, SHARP, Ultrasonic, etc.

Infrared Sensor

Infrared sensors use the infrared radiation to detect some object & gives information about it.

Infrared (IR) sensors are sensitive to infrared range. Since IR is invisible to human eyes, it will not disturb humans if used in devices that project the light out. If a device needs light to measure a large distance for navigation purpose, IR can be used without attracting attention or disturbing anyone.

Application of IR sensorIR sensor is the most basic sensor & it's used in basic

applications.

IR sensor has an emitter & receiver pair. The emitter LED emits IR & if the surface near to the emitter is black thenthe IR light gets absorbed & the receiver doesn't get any value, but if the surface is reflective(white in color) then the IR light gets reflected & the receiver receives a logical HIGH.

So an IR sensor can be used basic applications like making a Linefollower

in which the bot needs

to detect a line & follow

the line.

Application of IR sensor(cntd.)IR sensor can be used as a digital as well as an

analog sensor.

In the circuitry of an IR sensor there has to be an amplifier which will amplify the very small amount of signal received from the receiver.

We generally use an Opamp as an amplifier which amplifies the input of the

receiver & the amplified voltage

value can be used in operating

the bot that your are making.

SPECIFIC USAGE OF IR SENSORS

This sensor can be used mostly for indoor applications where the effect of ambient light is minimum.

1.Line follower : Most of you must have used them.

2. Block detection: This sensor can be used to detect a block.

Limitations of IR Sensor

1. IR sensor is very sensitive to ambient light.So the lighting conditions of the ambient during it's use should be such that it affects the least.

2. Applicable in a very short range. So it can't be used as a long range sensor.

3.Sometime two IR sensor may not be identical, so they need to be calibrated during there usage.

TSOP SENSORS

TSOP sensor is a series of IR receiver which is capable of receiving IR radiation modulated at some particular frequency.

The working is same as IR sensors but it's a

receiver. We need to use an LED to do the

work of an emitter and we can

modulatethe signal by providing

an electric signal which will

generate the required frequency

for detection.

Application of TSOP sensor

The range of TSOP is more than the common IR sensor. The range is around 15 cm & this can be varied using the circuit which is used.

As TSOP only works in a particular frequency, it doesn't get affected by the ambient light condition.

So this sensor is perfect for medium range object detection.

The commonly used TSOP is TSOP1738 which detects radiation at 38 Khz frequency.

Circuitry of TSOP Sensor

To generate the particular

frequency, timer circuit

using NE555 is used and

by calibrating the pot in

the circuit, we can adjust

the frequency.

The output of TSOP is

LOW when it receives the

pulse & HIGH otherwise.

TSOP SENSOR MODULE

Advantage of TSOP over IR Sensor

• The ambient conditions hardly affect the data given by the Sensor.

• The range of TSOP(around 5 cm to 25 cm) is more than normal IR sensor.

• As the range can be modulated, it's very convenient to use TSOP which can change its working range according to the given parameters.

Ultrasonic Sensor

Ultrasonic sensors are mainly used to measure the distance of the obstacle and speed of air or water.

They can also be used to measure the amount of liquid in tank, as humidifiers, Burglar alar, non-destructive testing etc.

How ultrasonic sensors work?

Ultrasonic sensors generate high frequency

(18000 Hz) sound waves and evaluate the echo which is received back by the sensor. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to the reflecting object.

Ultrasonic Sensors structure

Most common ultrasonic

sensors has one receiver

and one emitter.

Both of these can be on

a single board or on

different boards.

Advantages of Ultrasonic Sensors

• Discrete distance of moving objects can be measured.

• The received values doesn't gets affected by colors of the object.

• Resistance to external disturbances, such as IR radiation, Vibration, ambient noise,etc.

• The range of detection is very large which makes the Sensor useful in many applications.

• Highly accurate within a range.

Applications of Ultrasonic Sensors

• Ultrasonic sensors are one of the best sensors for accurate distance measurements within a given range.

• This sensor can be used anywhere where task is to detect some object within a distance or maintain a specific distance from a given wall etc.

• There can be many other application where this can be used trickily.

SHARP SENSOR

SHARP sensors are very accurate distance measuring analog sensors that gives an analog output based on the distance of the object from the sensor.

The sensor readings are highly accurate(within a range ofcourse).

There are different SHARP sensors available with different range of application.

SHARP Sensor

SHARP sensor pin diagram

is shown.The output given

by the sensor is not

proportional to the distance

of the object from the sensor.

There is a characteristic

curve for the output given by

the sensor.

SHARP Sensor(cntd.)

The shown curve is the characteristic curve of a

specific sensor.

The portion of the

curve after the peak is

used to measure the

distance.

It's clear that the output

isn't proportional to the

distance of the sensor.

Distance Measurement

We need to linearize the curve to find the distance

given the voltage output.

For the previous curve & sensor, the

equation y= 20.99*x + 0.19 fits where

y is the voltage output & x is the inverse

of the distance(in cm).

This gives a range for the sensor,the

voltage range is (0.45V, 2.8V) & the

corresponding distance is (7.5cm, 80cm).

The characteristics of this sensor can be applied

in many projects & the results are also very accurate.

• SHARP sensors are a popular choice for many projects that require accurate distance measurements.

• This is also a kind of IR sensor which is more economical than sonar rangefinders, yet it provides better performance than other IR alternatives.

• The analog output can be used in many way by the microcontroller. The analog value can be converted in digital value, or it can be compared by putting a threshold, or 2 SHARPs can be used to match the distance, etc.

• There is almost no effect of the ambient lights, so this sensor is a very convenient to use as an electronic sensor.

Advantages

Disadvantages

• One major issue with the SHARP sensor is going below the minimum sensor range. This is when an object is very close to the sensor & the output tells your robot that the object is very far, whereas it's very near.

• Another issue is the narrowness of the IR beam. In getting high accuracy, a thin beam is ideal but the problem with a thin beam is that, if it's not pointed exactly at the object, the object might become invisible

So before using SHARP sensor, above limitations should be taken care.

Other Useful Sensors

Few others sensors are:

• LM35: This is an IC which is used to measure temperature. The analog output of this IC is

• proportional to the temperature in *C.

• Humidity Sensor: This sensor is used to measure the relative humidity. One such IC used for this purpose is SHT71.

• Acceleration Sensor: Accelerometer is usedto measure acceleration about some axis. One such IC used is ADXL330.

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