Upgrading Keyless Electronic Lock

Design and Construction of a radio-controlled enabled electronic lock

Wireless (radio) Electronic Lock

Introduction

My Bluetooth wireless lock was worked admirably for the last year but occasionally it takes a long time to pair. The "Users" in the house complain about having to dance on the doorstep while the pairing goes on. Picky, picky! However, I see the point so it needs some modification.

Trigger Options

I broached the idea of having a simple pressure mat but was again vetoed on drilling through the wall. I could go down the road of buying more expensive low power bluetooth modules that would always be paired by leaving the transmitter on. Or I could relax the security and just use a plain and simple wireless link.

Radio Wireless

I had about a 4 hour window at the weekend so I needed to make something that was operational without getting bogged down in things. I've also 'done' bluetooth so wanted to try something different. The decision was to go for a simple wireless link. Rather than using xbee, I went for a very simple wireless 'blibber', pre-constructed and an associated wireless receiver. The idea is to swap-out the bluetooth and replace everything with wireless. Same box, same wiring.

The TX/RX pair work out-of-the box. As long as the transmitter button is held down, a logic 1 appears on the appropriate receiver pin. So I pulled the timer circuit out of the bluetooth transmitter box I built with the aim of putting it in the receiver. I changed the timing capacitor, bringing it down form 100uF to 33uF and drove the circuit from 5v rather than 3v. This gave a timer delay of 10 seconds which seemed a good compromise of how long the door should be held open for.

Here is the original delay circuit diagram

And this was the circuit salvaged from the old bluetooth transmitter circuit

Interfacing

To wire the timer to the output of the RX module means essentially replacing the 'switch' on the above delay circuit. However, the RX using CMOS which has a drive capacity of 3mA whereas to charge the capacitor quickly, we need considerably more drive current than that. I Added a small NPN transistor to give this extra drive so the modified circuit diagram is now:

Construction

This all worked fine on a breadboard. As I will be taking the arduino out of the circuit, I need something that will give me 5V to drive the RX and timer circuit. A Simple 7805 regular can be used to bring the 12V supply as needed. I used a kiwipatch board as this has provisions for adding such a voltage regulator. This board thus contains the Regulator, The RX module and the driver transistor. The output feeds the timer module which in turn feeds out to the door relay (as before).

Results

It all works as expected. Nothing really difficult here as it was just wiring modules together. We now have a blibber that when pressed, immediately unlocks the garage door for 10 seconds which prevents all the dancing on the garage door mat. I will miss that but we need to keep the "Users" happy!

November 2018