A Keyless Electronic Lock

Design and Construction of a bluetooth enabled electronic lock

Wireless Electronic Lock

Introduction

Having recently moved house, the side door to the garage is outside the house which has its own lock. As I'm a garage-sort-of-guy, I often find the door locked and don't have the key with me. Even when I do it is fiddly to unlock, especially if carrying something. I needed to do something about this as it is frustrating so I decided to put an electronic lock on the door.

Trigger Options

Once the door has an electronic lock, there are various mechanisms available to open it.

• A keypad
• RFID
• Wireless
• Fingerprints
• Butt scanner

I don't really want a keypad/RFID or an wireless blibber as that means having to carry a 'key' of some kind, a keypad is annoying and a butt scanner is just wrong. It comes down to a compromise between security and ease of use. Since the door is only 3 paces from the front-door, I was thinking a pressure mat inside the house would be useful so that when I step out, the garage would be unlocked (regardless whether I want to go in there or not). It would then auto-lock after 5 seconds or so. That seems a fine no-brainier option to me.

The Physical Lock

Electric locks come in Fail-Secure and Fail Safe falvours. I needed a Fail-secure version. I toyed with the idea of having a separate electronic dead-bolt but decided it would be more useful to reuse the existing mechanism and put in an electric latch-plate. The existing key could then be used if necessary. This required more mechanical grunt-work but would be more useful in the long run.

The door is aluminium framed. This meant getting an angle grinder in there with a few shims and drilling through the internal wall to bring out the lock electrics. A few hours and a lot of dust later we were set.

Operating the Lock

The locked worked on 12V DC and required 450mA to open it. I made a small box that contained a 5V relay board to switch the 12 volts to the lock. As this will be mounted near the lock, it has a push-switch to allow the lock to be operated from inside the garage to allow easy exit. A parallel 5V input is brought out which can be used to remotely open the lock.

Remote Triggering

My initial thoughts were to bring the trigger through the garage wall, into the house and have a pressure mat just inside the front-door, no power supply, just a simple switch. However, my wife was not keen on me drilling wires through the walls. I could have gone through the garage roof, into the house roof and back down the walls but to be honest, I did not really want another day of fumbling around in the dust and muck. So I needed a plan-B. If fact, a plan-B and a plan-C.

Reed Switch

The first option was do do something simple that worked. I found a reed switch in my toolbox and decided that would work fine for a Plan-B. Taping this to the inside of the garage door meant you could then open the the door with a strategically placed magnet. Not the most secure option, but a lot better than leaving the door unlocked. No wires in the house and a lot easier than fumbling with a key. It does mean you have to have a magnet handy but we keep one just inside the front door (as does everyone!).

This is the basic garage door opener circuit. It uses a 5v regulator and a remote input that (in the case of plan-B) will be a 5v switched input from the reed switch. There is a push-switch on the box that allows the door to be opened from the inside of the garage.

Wired it together and tested the push switch. It does not trigger the relay. After a bit of fault-finding and thought, I put this down to the large surge of current into the relay was affecting the regulator. So I put a capacitor between the regulator output and ground to buffer this. Initial testing shows that this appears to have solved the problem.

Here is the control box. Just a few switches and a relay. The choc-block is connected via a wire to the reed switch which is used to open the door by placing a magnet in the correct position. So all pretty simple and a good place to start.