Internet controlled door lock

I'm new at Arduino, infact this post is mostly about what parts I should buy to get started.

Here is what I wish to accomplish: I want a door to unlock when I enter a password on a website.

I know that I'll need an Arduino-board and an Ethernet shield, but several variations exist, and I don't have the knowledge to choose between them, so suggestions are welcome :-)

The door-lock requires a 12v DC signal, so I'm think it'll need a relay to turn it on/off as I please. Does a pre-built relay-shield exist, or will I need to build my own? If so, I would like suggestions on what parts I'll need for that, perhaps even schematics on how to assemble it?

Once I have my hardware, I'm sure I can get the programming to work :-) If not, I've noticed that there are lots of tutorials out there, so I don't think that will be a problem. (Also this isn't my first time programming micro processors.)

But long story short: What would your shopping-list look like, if you had to complete this project?

I would go for an Arduino Uno or Duemilanove. Easiest to get started with, and its most compatible with shields.

If you don't mind a ScoobyDoo sandwich style solution, then you could stack a relay shield (yes they exist) onto an Ethernet shield onto the Uno, and you won't have to do any soldering at all!

You can power the Arduino from a 12V supply (wall-wart check it can provide enough current for the lock).

Strip the positive connection from the power supply before it reaches the low voltage plug and route this to one side of your relay's switch, ready for it to power the lock.

Before buying the shields, check in their datasheets that they don't conflict by using some of the same pins.

Good luck and let us know how it goes :)

I found theese two, those are the ones you ment, right? ← Arduino Uno ← Ethernet Shield

(Sorry about the pages beeing in Danish, but I wanted to link to the site I will likely be buying from)

I went for the Arduino Uno instead of Duemilanove, since from what I can tell, the only difference in specs is that Uno has about twice as much memory, and when they cost the same, the choice seems clear.

I havn’t been able to find any relay-shields, could you by any chance provide a link to an example of one?

If I can infact get a pre-made relay-shield, it sounds like all my hardware-requirements will be met, without me even warming up my soldering iron :smiley:

...and just as I had given up, my friend mails me a link to a relay-shield :-D

Do you think this would be compatible with both the Arduino Uno and the Ethernet Shield?


This web site is pretty good for checking if they are compatible:

Very cool site, makes it quite clear to compare shields.

Si said to check for pin conflicts, and the Ethernet Shield uses pin D4 for the SD-card (I won't be using the SD-card), and the Relay Shield uses Pins D4-D7.

Does that count as a conflict, if I won't need the SD-card on the Ethernet Shield? Won't the Ethernet shield just ignore activity on pin D4 then?