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Reed switch

A magnetic reed switch is a switch that change it's state whenever a magnetic field is present.
Magnetic reeds are cheap and really easy to find online.
They have a lot of practical uses like checking if a window/door is open or not.
We will use them in our A-H-A project.
There are two options of these magnetic switches.
The N.O. (normally open) and the N.C. (Normally Closed) ones.
Normally Closed (NC) is a reed switch that the current passes when the magnet is not present.
The same type of reed is also called Normally Open with magnet.
On the other hand a reed switch is called NO, when without the presence of a magnetic field the current does not pass (open circuit).
The same type of reed switch can be also called Normally Closed with magnet.
In alarms it is most common to use a NO or alternatively called NC with magnet reed switch since the alarm when is broken or being cut by thieves then the circuit results open/broken even if the magnet (door) is in place.

Reed Switches
Reed Switches

That's why most residential alarm systems use NO or alternatively called NC with magnet reed switches.
More about reed switched will be discussed in other theoretical articles. If you are interested you can visit the dedicated wikipedia page.
Let's find out how we can connect this switch into an arduino board.

...continue reading "Connecting a magnetic reed door switch into arduino"

AHA Project RFID Part 2

In this tutorial we will see how we can recognize persons using our RFID reader.
Two LEDs will be added at the project in order to get some better user experience.
A "security line" will be also added. The concept of the "security line" is pretty simple.
If the line get's 5V (is HIGH) then arduino knows that the RFID reader is working correctly otherwise the RFID reader is broken (or the communication between arduino - RFID reader).
As always we will make an "object based" approach.
From the first article of RFID we can find the TAG IDs.
...continue reading "Connecting 125Khz RFID module to arduino – Part 2"


In this tutorial we will see how we can connect a RDIF reader into arduino.
We are going to use a 125 Khz RFID module  that can be bought from seeedstudio.
Some 125 Khz tags are also needed. We bought them from ebay but you can also find them on other online shops.
This guide is the first of a series of articles.
Starting from this article we are going to construct from scratch a home alarm based on arduino duemillanove.
Since the project is big we are not going to see a lot of details of each part / sensor.
In the future we will try to cover the theoretical gap.
These series of tutorials will be easy to understand and will help you to construct step by step the "A-H-A" (Arduino Home Alarm) project.

...continue reading "Connecting 125Khz RFID module to arduino – Part 1"