SENSORS: SENSORS CONTENT: CONTENT INTRODUCTION TYPES OF SENSORS IR SENSORS BUMP SENSORS SONAR PHOTO RESISTOR COLOUR SENSOR ACCELEROMETER INTRODUCTION : INTRODUCTION Sensors are the input devices to the robot.They are the means that the robot uses to connect to the external world.For a better understanding the sensors are like eyes for you and like a mouse to a computer.They play a very important and vital role in a robot.Sometimes it can be the winning factor between your bot and another bot in a competition depending on how well you calibrate your sensor to the surroundings. INTRODUCTION: INTRODUCTION There are different types of sensors available in the market depending upon your need and requirement.The various types of sensors will be dealt with in the following slides.Some of them are used so frequently and some are used only in complex robotics and at the same time hard to acquire.But none the less you should have a sound knowledge of all types of sensors to get more creative INTRODUCTION: INTRODUCTION Last year,the bots that we built for ROBOCON also depended heavily on sensors such as BUMP SENSORS IR SENSORS(ANALOG) IR SENSORS(DIGITAL ) The biggest task in making the sensors work properly is tuning it with the ambient light and checking the output voltages and to make sure that the readings do not change with the ambient light.Now lets see the types of sensors. TYPES OF SENSORS: TYPES OF SENSORS IR SENSORS BUMP/TACTILE SENSORS SONAR PHOTORESISTOR COLOUR SENSOR ACCELEROMETER SHARP IR SENSORS DIGITAL COMPASS ENCODER LOAD AND TORQUE SENSOR MERCURY TILT SWITCH Slide 7: As we all know that the sound emitted is reflected from the surface. The uC gives the go command to the emitter due to which the sound is emitted.At this instance the timer is started. When the sound returns to the receiver a square pulse is sent back to the uC.At this instance the timer is stopped.Depending upon the time taken for the sound to travel back and forth the distance of the obstacle from the sensor is determined. IR SENSORS: IR SENSORS IR stand for infra red rays which are just below the visible spectrum.These rays have wavelength which are just lower than the spectrum of the colour red. These rays are not visible to the naked eye. They are the most commonly used sensors. They are used in line followers,grid counting,motion detection and obstacle detection. Slide 9: We shall now look into the basic concept of this kind of sensors. There is an IR led which emits IR radiations. Just beside this led is fixed a photo transistor The led emits the radiation and the photo transistor receives the radiations. Depending upon if the radiations emitted are reflected and received by the photo transistor or lost in space an obstacle or a line is detected by noting the change in the output voltage of the photo transistor. Slide 10: The circuit diagram has been given below: Slide 11: R1 is to limit the flow of current thru the emitter. R2 should be larger than the greatest resistance of the photo transistor.This way the Vout will be close to zero when there is no signal. L1 is the emitter and T1 is the detector. The change in readings is seen on the Vout signal. Handy Tip:To check if your IR led is emitting properly,look at the led through a camera. Slide 12: The Vout signal can be given directly to the uC as an analog signal to the ADC pins or can be given to a comparator to convert to a digital signal. The circuit diagram with a comparator is shown in the next slide. A variable pot for ref. voltage is connected to the comparator whose voltage is the mean of the voltages of Vout max and min. The output of comparator is high or low Slide 14: The usual comparator used is LM324 or LM358. The pin config of LM324 is given. Slide 15: These type of sensors are the most commonly used sensors in simple robots. There are placed in a row to detect a line.The number of sensor pairs used depend upon the accuracy required for following the line. BUMP SENSORS: BUMP SENSORS Bump sensors are used on the edge of the bots body to detect walls or obstacle and avoid it. When the bot hits the obstacle in front of it the switch on the bump sensor gets depressed and this is how the bot knows of the presence of the obstacle in front of it and it tries to avoid it. Slide 17: The diagram of the bump sensor is given below. When the switch gets depressed it flips from the gnd to Vcc and the signal goes high which passes on the info to the uC . SONAR: SONAR These type of sensors are used to determine the distance of each obstacle from the sensor. In this type,there is one emitter and one receiver. The basic idea here is to determine the time taken for the sound emitted to reflect back from the obstacle and hit the receiver. Slide 19: The diagram of a sonar sensor is given below. PHOTORESISTOR: PHOTORESISTOR These type of resistors change the output voltage depending upon the amount of light falling on the surface of the resistor. The analog output of this sensor is given directly to uC input pin. The image of this kind of sensor and ciruit diagram is shown in the next slide. Slide 22: Fig 1 is a image of the sensor. Fig 2 is the case where the Vout increases with the amount of light incident. To find the value of the resistor used in the curcuit calculate the resistance of the photo resistor in the lowest light and the max light conditions and use the values in the formula R= sqrt ( r_min * r_max ) COLOUR SENSORS: COLOUR SENSORS These type of sensors are used to help the bot differentiate between colours and decide on the appropriate actions. The image of a colour sensor is shown in the next slide.We make use of the photo sensor to differentiate between colours . Slide 25: In the above pic we place three leds of green blue and red and the photo resistor in between them. Now each colour led is switched on for a period of time one by one and the readings of the photoresistor are noted. After getting the readings of the different colours we compare how different each reading is from the calibrated reading of every colour . This way whichever calibrated value is closest to the recorded values ,indicates that the object in front is of that colour . Slide 26: This happens because we know that when a light of a particular colour is incident on the same coloured object it reflects with more intensity than when a different coloured light falls on a object.Based on this we enter the calibrated values of all the colours required into the system and when the robot comes across the recorded value it compares it with the closest value. ACCELEROMETERS: ACCELEROMETERS These type of sensors detect any form of accelaration on the bot they are mounted upon.There are tiny micro structures that bend due to momentum and gravity.This in turn give out an electrical signal. There are many applications for these accelerometers in almost all electronics.