Digital sensors

Pushbutton

Pushbutton makes contact when pressed and breaks when the button is released. Together with a resistor this gives digital signal.

Reed relay

Reed relay makes contact in presence of magnetic field and breaks when the field is absent. Together with a resistor this gives digital signal.

Photo interrupter

Sensor contains infrared emitting diode and a phototransistor. Sensor changes state when some obstacle is inserted into the gap between the diode and the phototransistor. Sensor has three pins. Pin 1 (marked '-') is ground, pin 2 is power (Vcc), pin 3 is output. High voltage on pin3 means no obstacle, low means presence of an obstacle.

Remark: Together with appropriate mechanical system this sensor can be used to count rotations or to detect when mechanism reached prescribed position.

Rotary encoder

Rotary encoder has two switches and an axis. When axis is rotated switches produce sequence of pulses. Counting pulses we can detect rotational position of the axis. High speed high resolution rotary encoders use photoelectic switches. In fact, it is possible to use a disc with holes attached to an axis and a pair of photo interrupters as a rotary encoder. Simpler rotary encoder has mechanical switches. We have simple low resulution encoders which can serve as elements of user interface: user rotates a knob and encoder converts this to digital signal. More information about rotary encoders and examples.

Digital Hall sensor

Hall sensor detects magnetic field. We have sensor module using A44E sensor chip which changes output when field is strong enough. The detection threshold is rather high, so we need strong magnet to trigger change.

Passive infrared motion detector

Sensor contains a matrix of elements sensing infrared radiation and a circuit detecting change. A person or an animal emits infrared radiation. When in movement a person causes changes in level of infrared radiation, which is detected by the sensor. Sensor has one output line with high level signalling that change was detected. Sensor has three pins, marked Vcc (power supply), GND (ground) and OUT (output line).

Remark1: Such sensors are widely used in alarm system and to turn on lights when movement is detected.

Remark2: Internally this sensor is quite complex. However, externally it behaves as simple digital sensor.

Infrared proximity sensor

This sensor changes output when obstacle is within short distance.

Analog sensors

Photoresistor

Photoresistor has resistance which depend on ambient light. Combined with normal resistor gives voltage depending on light.

Thermistor

Thermistor has resistance depending on temperature. Combined with normal resistor gives voltage depending on temperature.

Linear Hall sensor

Linear Hall sensor produces voltage proportional to magnetic field. Our sensor modules contains A49E sensor chip. One module just gives signal from the chip. Another module additionally contains a comparator so it provides both digital and analog signal.

Complex sensors

Ultrasonic range sensor

The sensor contains ultrasound transmitter and receiver. The sensor has four connections: power supply (Vcc) which must be 5V, ground (GND), Trig and Echo. Short impulse on Trig turn on ultrasound transmitter. Change on Echo signals that echo was detected by the receiver. The "Ping" example in "Sensors" group in Arduino shows how to use it.

Remark: The Arduino example assumes that a single line works both as Trig and Echo: the example has to be modified to work with our sensor.