It was easy enough to look through the text string to find the relevant password and act accordingly.
The cellular shield communicates with the microcontroller using UART serial comms, sending cryptic text strings to show what is happening in the GSM cellular receiver.
I also added the ability for me to enable/disable the whole system using an SMS and my own master code, as well as a feature where I could change the regular access code at any time. My first working solution used SMS messages, where the gate was opened on reception of a text featuring a four letter password. A-HA! I could tap into the button on this remote control and have my system sit in the Playroom (or anywhere in range of the gate control receiver)!Īrduino + Cellular shield + Gate remote = :)Īfter figuring out the required hardware I moved on to thinking about how I would control access. Then one day I stumbled across an unused remote control for the gate – its plastic buttons had broken off and it was just lying in the kitchen drawer. Of course I could add some XBees or other wireless point to point link, but I didn’t feel the extra expense and complexity would be worth it. But as I spend most of my time in the Playroom I wanted to be notified visually or audibly of guests arriving, and dreaded the thought of running cable from inside the house to the Playroom. I first thought that I would tap into the intercom receiver’s gate “open” button, maybe close the connection with a relay.
The next problem would be how to open the gate remotely. I browsed around the web and read over a couple of forums where others had discussed similar GSM-telemetry Arduino projects, and settled on Sparkfun’s Cellular Shield, based on the SM5100B GSM/GPRS module. Once I had decided that I would be using the Arduino platform as a base, I then searched for a suitable GSM shield. Now it has a fridge and a Samsung LED HDTV, and the piano has been replaced with my workbench.
It has its own bathroom, some comfy couches and used to feature cupboards full of toys and games and even an old piano.
*the Playroom was given its name when my parents built the room for my sister and I to play in when we were children.
Coming from a background working with PICs and AVRs from scratch, it was actually quite nice to spend more time tweaking a mostly working design, as opposed to tweaking a design to be mostly working.
But my research was already consuming much of my time, and I took the path of choosing the Arduino platform, for its plug ‘n play attitude, minimal setup and well documented pre-written libraries. I could sit and design an elegant solution featuring only the necessary electronic components, using power-saving design techniques and choosing just the right microcontroller for the job based on number of used IO pins and peripheral features. And some of you seasoned electronics engineers will think WHAT! WHY USE ARDUINO WHEN YOU CAN BE 11.8x MORE EFFICIENT USING A CUSTOM MICROCONTROLLER-BASED DESIGN! Which is true. At the time I was busy finishing off my Master’s degree in electrical engineering, where I focussed on wireless communications, designing custom PCBs for a platform using Microchip PIC18F microcontrollers. I had recently been exposed to the world of Arduino by my friend and collaborator Tegan Bristow and thought this would be a great problem to solve using the Arduino platform, learning as I went along. ZZZzzzz BORING! I figured why not let my guests let themselves in, using their mobile phones! And so the idea of GSM-enabled gate access control was born. One solution to this problem is to add extra intercom extensions to the Playroom and the braai area.