About Reed Sensor
A reed switch is type of sensor works with magnetic field. Reed sensor is normally open naturally
before exposing to magnet and the switch is closed when it found magnet around it. If you place magnet around the reed switch then it becomes closed and circuit will start working and pass the signal to the circuit. You may find many types of example over the internet how to connect and interface with 89C51 microcontroller. To make this sensor work it is must to have magnetic field around it, then the sensor will become closed. Module will work with 10K Ohm resistor which is included with every package. Its a very low cost sensor available in the market and online websites.
How Reed Switch Sensor Works
As mentioned above, Reed Sensor is a magnetic sensor which works when if founds a magnetic field 
near. When the sensor is exposed to magnetic field, two ferrous pins equipped inside glass shields comes together because of the magnetic fields. This way switch becomes open and capable of passing current or signal through it. Then microcontroller 89C51 or any other MCU detects the high signal on the pin then intended function starts working inside the microcontroller 89S51 or any microcontroller. Now when the magnetic field is removed then two pins inside the sensor separates from each other and becomes open. This is the state when the sensor stops pass signal to the microcontroller.
Specifications and Features of Reed Switch Sensor
Sensor consists of two metal pins inside the a glass tube that comes closer when it found magnetic
fields and becomes open when magnet is removed. The sensor can carry approx 1.2A current. Its a very inexpensive module sensor can be used in every environmental condition, atmosphere has not impact on this. It works perfectly with accuracy in -50 C to +150 C temperature approximately. Its a very small and easy to install any where with the length of 45mm but it comes in various lengths and can be used in projects and applications as per the need. It has following basic features
- Naturally its an open open reed switch, when gets magnetic fields then it becomes closed.
- Normal Working voltage level is 3.3Volts to 12Volts.
- Uses More than 15mA.
- Output Signal format is in zero and one, Means 0 and 1.
- Dimensions: 1.57 in x 0.55 in x 0.28 in and 0.18 oz (5 g).
- Uses voltage LM393 comparator.
Interfacing Circuit is Given Below
Circuit and diagram reed switch or sensor to connect it with microcontroller. Interfacing is so simple and easy to understand due to its low pin count, it has only two pins, and how to connect with 8051 is given below, you may use same circuit with any microcontroller that you know and want to build circuit.
