Sometimes padlocks, zip ties, sternly-worded signs and keyed ignitions just don't cut it. Maybe what you're looking for is something more like...

...a web-enabled RFID interlock loosely based on 23b's Open Access Control system? Indeed! This is a horrible photo, but inside the lovingly-crafted cardboard box is a custom-made Arduino shield, an Arduino Ethernet, some wiring, and then the visible RFID reader, buttons, and LEDs. Also there's a piezo speaker in there.

Off to the side is a relay board with a transistor and 120V 10A relay that switches stuff off and on to its heart's content.

Its purpose? To get spliced in between the critical wiring of whatever you want to control, and then you can control its usage via a separate web server and database.

For example, effective parent control over an Xbox; keeping noobs out of the pantry; making sure only certified people use the laser cutter; having the coolest high-tech bouncer for your party ever, etc.

For code, schematics and circuitry, check out https://github.com/zyphlar/open-access-control-minimal-http WARNING, there is an error in the circuitry here. One of the pins from the shift register isn't going to the LCD screen as intended. The webserver component isn't uploaded yet either; the interface simply relies on  a webserver (in the code at http://10.1.1.1/~access/access?id=YOURID&device=THISDEVICE ) which returns ^username|OK$ when YOURID is a valid ID for accessing THISDEVICE. The username is then displayed on the LCD.

The code is also useful for its Wiegand26 Arduino library, which lets you use any Wiegand-compatible RFID readers/keypads desired.

Here are some photos:

[caption id="attachment_236" align="alignleft" width="300" caption="Old version of the Eagle board layout for the shield"][/caption]

[caption id="attachment_237" align="alignleft" width="300" caption="Prototyping the shield on our laser; didn't work out."][/caption]

[caption id="attachment_242" align="alignleft" width="300" caption="Shield fabricated by Seeed"][/caption]

[caption id="attachment_235" align="alignleft" width="300" caption="Prototyping the relay board on the laser; worked well!"][/caption]

[caption id="attachment_238" align="alignleft" width="300" caption="Selecting relays to use"][/caption]

[caption id="attachment_249" align="alignleft" width="300" caption="Assembled relay board"][/caption]

[caption id="attachment_248" align="alignleft" width="300" caption="Assembled shield"][/caption]

[caption id="attachment_247" align="alignleft" width="300" caption="Assembled shield and Arduino Ethernet"][/caption]