Open doors with a Raspberry Pi and RFID module

Lead Image © wittaya jitchatree,

Open Sesame

A Raspberry Pi combined with an RFID module can open doors automatically, but only if proper access rights are presented.

People who let their cats outdoors at night know how difficult it is to get up at 3:00am to let the cat back inside. The alternative is to build a cat door, but then you run the risk of inviting other animals into your home. Help is on the way with an RFID-controlled door that truly allows only your cat to get inside.

RFID Technology

Radio frequency identification (RFID) technology uses radio waves to identify objects. This technique is older than most would believe. Friend or foe recognition by means of secondary surveillance radar was already in use during the Second World War. Today, RFID is applied to all kinds of object identification tasks, access control, anti-theft security, and even card payment systems.

An RFID system consists primarily of a transponder and a device that can read the transponder ID. In simple terms, the reader creates an electromagnetic alternating field that provides power to the transponder. This causes the transponder to influence the characteristics of the alternating field in such a way that the reader can unambiguously identifiy the field.

The result is a contact-free exchange of identification information. The devices used for identification normally use NFC (near-field communication), so the transponder must be in close proximity of the reader. In the project described here, the distance should be about 3cm.

The Door

A simple piece of plywood can be used for the cat door (Figure 1). The important thing to remember is that the door has to be 1mm smaller than the frame in which it will sit. You can attach the spacer strips to frame the door.

Figure 1: A cat door design.

A small servo motor raises the door via a string (Figure 2, left) and lowers with the help of gravity. The RFID module should be right next to the entrance. The entire construction process should only take about two or three hours.

Figure 2: On the left, you can see a view of the back of the door. To the right is the entrance. The RFID module is on the entrance side.

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