Connecting a reed switch

A reed switch is a small device that when the device is exposed to a magnetic field, the two materials inside the switch pull together and the switch closes. When the magnetic field is removed, the two materials then separate and the switch will open.

Here is a picture of the reed switch breakout we will use in this example There are kits of sensors you can buy and this is a common one.

reed switch
reed switch

Here is the pinout in detail

Pin Label Arduino Connection
1 AO Analog input
2 G Ground (GND)
3 + 5 volt power
4 DO Digital input


We will connect this up, read the analog and digital signals and monitor using the serial monitor, we will then postion the reed switch near a magnetic source and see if the readings change.



Same as a previous example


[codesyntax lang=”cpp”]

// Arduino pin numbers
//D2 and A0 used
const int digital = 2;
const int analog = 0;

void setup()
pinMode(digital, INPUT);

void loop()




Here are the results you will see

As you can see  there are two basic sets of values

1/ The reed switch open/ no magnet – 0 and 1023
2/ The reed switch closed/ magnet present – 1 and 0


Here are links to the sensor kit

Ultimate 37 in 1 Sensor Modules Kit for Arduino from Amazon UK
Ultimate 37 in 1 Sensor Modules Kit for Arduino from Amazon US

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