IoT Bytes

Bits and Bytes of IoT

Basic IoT Sensors

Pradeep Singh | 27th May 2016


Sensors are hardware components that can detect events or changes in its surroundings, and then provide a corresponding output. Sensors are the eyes and ears of any IoT Project. Without sensors, there’s no IoT. Lets explore some of the commonly used sensors in IoT Applications.

1. Temperature Sensors:



The TMP36 is a low voltage, precision centigrade temperature sensor. It provides a voltage output that is linearly proportional to the Celsius temperature. It also doesn’t require any external calibration to provide typical accuracies of ±1°C at +25°C and ±2°C over the -40°C to +125°C temperature range.



LM35 series Temperature Sensor is a precisely integrated circuit whose voltage output is linearly proportional to the centigrade temperature. These sensors have an added advantage over kelvin calibrated sensors and do not require the subtracting of constant voltage from its output to obtain convenient centigrade scaling.


ds18b20The DS18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements and has an alarm function with nonvolatile user-programmable upper and lower trigger points. The DS18B20 communicates over a 1-Wire bus that by definition requires only one data line (and ground) for communication with a central microprocessor.

Waterproof DS18B20:

waterproof-ds18b20This sealed digital temperature probe lets you precisely measure temperatures in wet environments with a simple 1-Wire interface. The DS18B20 provides 9 to 12-bit (configurable) temperature readings over a 1-Wire interface, so that only one wire (and ground) needs to be connected from a central microprocessor.

2. Temperature and Humidity Sensors:


dht-11This DHT11 Temperature and Humidity Sensor features a calibrated digital signal output with the temperature and humidity sensor complex. Its technology ensures the high reliability and excellent long-term stability. A high-performance 8-bit microcontroller is connected. This sensor includes a resistive element and a sense of wet NTC temperature measuring devices.


dht22The DHT22 is a basic, low-cost digital temperature and humidity sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air, and spits out a digital signal on the data pin (no analog input pins needed). Its fairly simple to use, but requires careful timing to grab data. The only real downside of this sensor is you can only get new data from it once every 2 seconds

3. Temperature, Humidity and Barometric Pressure Sensors:


BME280The BME280 is as combined digital humidity, pressure and temperature sensor based on proven sensing principles. Its small dimensions and its low power consumption allow the implementation in battery driven devices such as handsets, GPS modules or watches. The BME280 achieves high performance in all applications requiring humidity and pressure measurement.

4. Temperature, Altitude and Barometric Pressure Sensors:


BMP180The BMP180 is a very high performance atmospheric pressure sensor designed for use in applications such as smart phones, tablet devices, sports devices, etc. The sensor has a pressure range of 300 to 1100hPa and the device also features low power consumption and small size, making it ideal for installation in mobile and hand-held devices.


MPL3115A2This pressure sensor from Freescale is a great low-cost sensing solution for precision measurement of barometric pressure and altitude. The MPL3115A2 has a typical 1.5 Pascal resolution, which can resolve altitude at 0.3 meters . It has interrupt outputs for ultra-low power usage, and a lot easier to read altitude with a built in altimeter calculation.

5. Motion Sensors:

PIR Sensor:

PIRPIR sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range. They are small, inexpensive, low-power, easy to use and don’t wear out. For that reason they are commonly found in appliances and gadgets used in homes or businesses. They are often referred to as PIR, “Passive Infrared”, “Pyroelectric”, or “IR motion” sensors.

6. Light Sensors:



A photoresistor (or light-dependent resistor, LDR, or photocell) is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity.



A photodiode is a semiconductor device that converts light into current. The current is generated when photons are absorbed in the photodiode. A small amount of current is also produced when no light is present. Photodiodes may contain optical filters, built-in lenses, and may have large or small surface areas.


A phototransistor is a light-sensitive transistor. A common type of phototransistor, called a photobipolar transistor, is in essence a bipolar transistor encased in a transparent case so that light can reach the base–collector junction.

7. Gas Sensors:

MQ-2 (LPG, Butane, Propane, Methane, Ethanol, Hydrogen, Smoke Sensor):


MQ – 2 is a flammable gas and smoke sensor detects the concentrations of combustible gas in the air and outputs its reading as an analog voltage. It is used for home or factory gas leakage monitoring devices, suitable for liquefied petroleum gas, butane, propane, methane, ethanol, hydrogen, smoke and other monitoring devices.

MQ-3 (Alcohol Sensor):


This alcohol sensor is suitable for detecting alcohol concentration on your breath, just like your common breathalyzer. It has a high sensitivity and fast response time. Sensor provides an analog resistive output based on alcohol concentration. The drive circuit is very simple, all it needs is one resistor. A simple interface could be a 0-3.3V ADC.

MQ-6 (LPG, Iso-Butane, Propane):

MQ 6 Gas sensor is used as LPG, Butane and Propane Sensor to generate alarm when there is leakage of these gases from the source. MQ6 is a highly sensitive gas sensor to petroleum based gases but less sensitive to Alcohol and Carbon di oxide. This simple sensor can be installed in the kitchen to give warning alarm if there is leakage of LPG.

MQ-7 (Carbon Monoxide Sensor):

MQ-7This is a simple-to-use Carbon Monoxide (CO) sensor, suitable for sensing CO concentrations in the air. The MQ-7 can detect CO-gas concentrations anywhere from 20 to 2000ppm. This sensor has a high sensitivity and fast response time. The sensor’s output is an analog resistance. The drive circuit is very simple; all you need to do is power the heater coil with 5V, add a load resistance, and connect the output to an ADC.

MQ-135(Air Quality Sensor):

MQ135This sensor is used in air quality control equipment for buildings/offices, are suitable for detecting of NH3,NOx, alcohol, Benzene, smoke,CO2 ,etc.

8. Distance / Proximity Sensors:

HC-SR04 (Ultrasonic Distance Sensor):

UltrasonicDistanceSensor The HC-HR04 ultrasonic sensor uses sonar to determine distance to an object like bats or dolphins do. It offers excellent non-contact range detection with high accuracy and stable readings in an easy-to-use package, from 2cm to 400 cm or 1” to 13 feet. It operation is not affected by sunlight or black material . It comes complete with ultrasonic transmitter and receiver module.

GP2Y0A02YK0F (IR Distance Sensor):

IRDistanceSensorGP2Y0A02YK0F is an Infrared proximity sensor made by Sharp. It has an analog output that varies from 2.8V at 15cm to 0.4V at 150cm with a supply voltage between 4.5 and 5.5VDC. The sensor has a Japanese Solderless Terminal (JST) Connector.

9. Motion / Direction / Location Sensors:

L3G4200D (3-Axis Digital Gyroscope):

L3G4200DThe L3G4200D is a low-power three-axis angular rate sensor. It has a full scale of ±250/±500/±2000 dps and is capable of measuring rates with a user-selectable bandwidth. It works great in gaming and virtual reality input devices, GPS navigation systems and robotics.

MPU-6050 (3-Axis Digital Gyroscope):

mpu6050The InvenSense MPU-6050 sensor contains a MEMS accelerometer and a MEMS gyro in a single chip. It is very accurate, as it contains 16-bits analog to digital conversion hardware for each channel. Therefor it captures the x, y, and z channel at the same time. The sensor uses the I2C-bus to interface with Controller.

ITG3205 (3-Axis Digital Gyroscope):

ITG-3200The ITG-3200 features three 16-bit analog-to-digital converters (ADCs) for digitizing the gyro outputs, a user-selectable internal low-pass filter bandwidth, and a Fast-Mode I2C (400kHz) interface. Additional features include an embedded temperature sensor and a 2% accurate internal oscillator.

HMC5883L (3-Axis Digital Compass):

HMC5883LHMC5883L is Honeywell’s  3-axis digital compass. Communication with the HMC5883L is simple and all done through an I2C interface. There is no on-board regulator, so a regulated voltage of 2.16-3.6VDC should be supplied.

FGPMMOPA6C / MT3339 (GPS Module):

MTK3339The GlobalTop FGPMMOPA6C is an ultra‐compact POT (Patch On Top) GPS Module, The module utilizes the  MediaTek new generation GPS Chipset MT3339  that achieves the industry’s highest level of sensitivity (‐165dBm )  and  instant Time‐to‐First Fix (TTFF) with lowest power consumption for precise GPS signal processing to give the ultra‐precise positioning under low receptive, high velocity conditions.

10. Imaging Sensors:

Raspberry Pi Official Camera Module:

Raspberry-Pi-CameraThis camera module is capable of 1080p video and still images and connects directly to your Raspberry Pi. Connect the included ribbon cable to the CSI (Camera Serial Interface) port on your Raspberry Pi, boot up the latest version of Raspbian and you are good to go.


OV7670/OV7171 (640×480 VGA CMOS Camera):

VGA_OV7670The ov7670 is an image sensor manufactured by Omnivision. It can provide the full functionality of a single-chip VGA camera and image processor in a small footprint package. The OV7670/OV7171 provides full-frame, sub-sampled or windowed 8-bit images in a wide range of formats, controlled through the Serial Camera Control Bus (SCCB) interface.

11. Magnetic Sensors:

Reed Switch:

reed-switchThe reed switch is an electrical switch operated by an applied magnetic field. It was invented at Bell Telephone Laboratories in 1936 by W. B. Ellwood. When the device is exposed to a magnetic field, the two ferrous materials inside the switch pull together and the switch closes. When the magnetic field is removed, the reeds separate and the switch opens.

Magnetic Switch (Magnetic Door / Window Sensor):

ReedSwitchMagnetic Switch is a small reed switch assembly specifically designed to alert you when doors, drawers, or any other aperture opens. These types of switches are primarily used in home security systems. One half of the assembly set on a window or door frame and the other attached to the window or door itself. When the switch set is separated from each other the contact is broken and triggers an alarm.

US1881 (Hall Latch):

US1881The US1881 is an integrated Hall effect latched sensor. Holding a magnet near the sensor will cause the output pin to toggle. This makes for a robust presence sensor. A reed sensor also works nicely, but can be limited by the glass encapsulation and size. A hall effect sensor is much smaller, but can handle less current than a reed switch.

SCT-013-000 (Non-invasive AC Current Sensor):


The split core type sensor, is particularly suitable for DIY projects. It can be clipped straight on to either the live or neutral wire coming into the building without having to do any high voltage electrical work. The measured current is alternative, and the sensor is calibrated to measure a max of 100A AC. 100A is the RMS value of the maximum current the sensor can handle.

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