Sensors for Robotics

Motion and Orientation Sensors

Accelerometer

Function: Measures linear acceleration forces and tilt
Types: Capacitive MEMS, Piezoresistive, Piezoelectric
Applications: Motion detection, orientation sensing, vibration analysis, fall detection
Examples: ADXL345, MPU-6050, LIS3DH

Types of Accelerometer

The 3 important types of accelerometers are:

Capacitive MEMS Accelerometer: Detects changes in capacitance instead of resistance. Most mobile devices use this type of accelerometer.
Piezoresistive Accelerometer: Measures vibrations by changes in resistance. Effective for measuring very slight vibrations, such as gravity vector.
Piezoelectric Accelerometer: Uses crystals or ceramics (like lead zirconate, lead titanate) that absorb vibrations and produce equivalent electrical signals.

Working Principle

The main working principle of an accelerometer is converting mechanical energy into electrical energy. When a mass placed on the sensor (which acts like a spring) moves due to acceleration, this movement generates an electrical signal proportional to the acceleration. This signal is used to measure variations in the device's position.

Accelerometers are available in both analog and digital forms and can detect static forces like gravity or dynamic forces in devices like phones and laptops.

Applications in Robotics

Motion detection and orientation sensing
Vibration analysis
Navigation systems
Fall detection in safety systems
Tilt sensing for balance control

Gyroscope

Function: Measures angular velocity and rotation
Types: MEMS, Fiber optic, Ring laser
Applications: Stabilization, navigation, motion control
Examples: L3GD20H, ITG-3200, MPU-6050

Working Principle

Modern MEMS gyroscopes use vibrating elements to detect changes in orientation based on the Coriolis effect. When the gyroscope rotates about any of the sense axes, the Coriolis Effect causes a vibration that is detected by a MEM inside the sensor. This signal is amplified, demodulated, and filtered to produce a voltage proportional to the angular rate.

Applications in Robotics

Stabilization systems for drones and robots
Navigation and orientation tracking
Camera stabilization
Balancing robots
Motion control in gaming and VR

Magnetometer

Function: Measures magnetic field strength and direction
Types: Hall effect, Fluxgate, Magnetoresistive
Applications: Compass heading, metal detection, position tracking
Examples: HMC5883L, LSM303, MAG3110

Working Principle

Magnetometers work on the principle of Faraday's Law of induction and magnetic properties of matter. Copper coils wrapped around a magnetic core detect fluctuations in magnetic fields, which induce current flow. Modern magnetometers use technologies like TMR (tunnel magnetoresistance) for higher accuracy.

Applications in Robotics

Navigation and heading determination
Position tracking in GPS-denied environments
Metal detection and mapping
Gesture recognition in combination with other sensors
Augmented reality applications

IMU (Inertial Measurement Unit)

Function: Combines accelerometer, gyroscope, and often magnetometer
Applications: Drone stabilization, robot orientation, motion capture
Examples: MPU-9250, BNO055, ICM-20948

Working Principle

An IMU combines multiple sensors (typically accelerometers, gyroscopes, and sometimes magnetometers) to provide complete motion tracking. The accelerometer measures linear acceleration, the gyroscope measures rotational rate, and the magnetometer (if included) measures magnetic field direction.

Modern IMUs often include sensor fusion algorithms that combine data from all sensors to provide more accurate orientation information than any single sensor could provide alone.

Applications in Robotics

Drone stabilization and navigation
Robot balance and orientation
Motion capture
Autonomous vehicle navigation
Virtual and augmented reality

Distance and Proximity Sensors

Infrared (IR) Proximity Sensor

Function: Detects nearby objects using IR reflection
Range: 2cm to 30cm typically
Applications: Obstacle detection, line following, motion detection
Examples: TCRT5000, QRE1113, GP2Y0A21YK

Working Principle

IR sensors work by emitting infrared light and detecting its reflection. The sensor consists of an IR LED (emitter) and a photodiode (detector). When the emitted IR light hits an object, it reflects back to the detector, creating a measurable electrical signal.

Applications in Robotics

Line following
Obstacle detection
Motion detection
Encoders
Color detection
Edge detection

IR Distance Sensor

Function: Measures distance using triangulation
Range: 10cm to 80cm typically
Applications: Precise distance measurement, mapping
Examples: Sharp GP2Y0A02YK, GP2Y0A710K

Ultrasonic Sensor

Function: Measures distance using sound wave reflection
Range: 2cm to 400cm typically
Applications: Obstacle avoidance, level sensing, mapping
Examples: HC-SR04, US-100, MB1240

Working Principle

An ultrasonic sensor generates high-frequency sound waves (40 kHz) and evaluates the echo received back. By measuring the time between emission and reception, the sensor can calculate the distance to an object using the formula:

Distance = Time × Speed of sound / 2

Most ultrasonic sensors like HC-SR04 can measure distances from 2 cm to 400 cm.

Applications in Robotics

Obstacle avoidance
Level sensing
Object detection in transparent materials
Mapping and navigation
Proximity detection

Time-of-Flight (ToF) Sensor

Function: Measures distance using light travel time
Range: Up to several meters with high precision
Applications: 3D mapping, gesture recognition, precise ranging
Examples: VL53L0X, VL53L1X, TMF8801

LIDAR (Light Detection and Ranging)

Function: Creates detailed distance maps using laser
Types: 1D, 2D (planar), 3D
Applications: Navigation, mapping, obstacle detection
Examples: RPLIDAR, Velodyne Puck, YDLIDAR

Position and Motion Tracking

Encoders

Types: Incremental, Absolute, Optical, Magnetic
Function: Measures rotation of wheels or motors
Applications: Position tracking, speed control, odometry
Examples: E6B2-CWZ6C, AMT102, AS5048A

Working Principle

A typical encoder uses optical sensors, a moving mechanical component, and a special reflector to provide a series of electrical pulses to your microcontroller. These pulses can be used as part of a PID feedback control system.

There are two main types:

Incremental encoders: Generate pulses as the shaft rotates, counting these pulses determines position change
Absolute encoders: Provide a unique digital code for each shaft position

Applications in Robotics

Motor speed control
Position feedback
Navigation systems
Robotic arm joint position sensing
Wheel odometry for localization

Potentiometer

Function: Measures angular position through resistance
Applications: Joint angle sensing, user input, simple position feedback
Examples: 10K linear potentiometer, 3590S precision pot

Linear Variable Differential Transformer (LVDT)

Function: Measures linear displacement
Applications: Precision motion control, industrial automation
Examples: Macro Sensors GHSE/GHSER Series

Environmental Sensors

Temperature Sensor

Types: Thermistor, Thermocouple, RTD, Digital IC
Applications: Thermal monitoring, environmental sensing, motor protection
Examples: DS18B20, TMP36, DHT22, MAX6675

Humidity Sensor

Types: Capacitive, Resistive, Thermal
Applications: Environmental monitoring, weather stations
Examples: DHT11, DHT22, BME280, SHT31

Barometric Pressure Sensor

Function: Measures atmospheric pressure
Applications: Altitude estimation, weather prediction
Examples: BMP280, BMP388, MS5611

Gas Sensors

Types: MQ series (MQ-2, MQ-3, etc.), electrochemical, infrared
Detects: Various gases (CO, CO2, methane, alcohol, smoke)
Applications: Air quality monitoring, leak detection, safety systems
Examples: MQ-2, MQ-135, CCS811, SGP30

Vision and Light Sensors

Camera Sensors

Types: CMOS, CCD, Thermal, Depth
Applications: Computer vision, object recognition, navigation
Examples: OV7670, Raspberry Pi Camera, Intel RealSense

Light Sensor (Photoresistor/Photodiode)

Function: Detects ambient light levels
Applications: Light-following, day/night detection
Examples: LDR, TSL2561, BH1750

Color Sensor

Function: Detects surface color (usually RGB)
Applications: Line following, color sorting, object identification
Examples: TCS34725, TCS230, APDS-9960

Working Principle

Color sensors work by detecting what colored light is being reflected off a surface. Each sensor typically has LEDs that illuminate with white light and a light detector. The white light hits the surface, some is absorbed and some reflected based on the surface color. The sensor detects the returning reflected colored light and determines the color.

Applications in Robotics

Line following robots
Color sorting systems
Object identification
Quality control
Environmental monitoring

Force and Pressure Sensors

Force Sensitive Resistor (FSR)

Function: Measures applied force/pressure
Applications: Touch detection, grip sensing, weight measurement
Examples: FSR400, FSR402, Interlink FSR

Load Cell

Function: Precise weight/force measurement
Applications: Weight sensing, force feedback, industrial automation
Examples: HX711 with strain gauge load cells

Pressure Sensor

Types: Absolute, Gauge, Differential
Applications: Pneumatic systems, weather stations, altitude sensing
Examples: BMP280, MS5803, MPX5010

Strain Gauge

Function: Measures deformation/strain in materials
Applications: Structural monitoring, force measurement
Examples: BF350-3AA, KFG series

Tactile and Contact Sensors

Bump Sensor

Function: Detects physical contact/collision
Types: Mechanical switch, spring-loaded
Applications: Collision detection, boundary sensing
Examples: Basic microswitches, roller switches

Working Principle

Bump sensors are simple switches that close a circuit when physical contact is made. When the sensor bumps into an object, the mechanical contact completes the circuit, sending a signal to the microcontroller.