door

This page was featured on slashdot on 2002/1/11. Here's how that went. You're all still welcome to email me at drewp@bigasterisk.com with your stories, ideas, and comments, though.

The front of the house. The windows on the left are to my room.

In my window sits a cheap barcode reader. It's powered by a computer power supply I ripped from an old computer.

Anyone who wants to get into the house can scan a barcode that they carry. A video store gave me a little keychain barcode which I'm using here. The scanner has a CCD; I don't have to slide the barcode. The scanner actually has a beeper that I can control from the computer. You can hear it beep from outside the window.

Here's the driver circuit I slapped together for the barcode reader. It's just a MAX232 chip that converts CMOS/TTL levels to the RS232 spec. The output connects to the serial port of one of my Linux boxes. That box runs a trivial python program to read a packet from the serial port and send it via TCP/IP to another computer in the house. The scanner interface program is now available here, and it now uses the pyserial module so it might run on mswindows too.

The receiving computer is connected to this K8000 experimenter board. I2C chips on this board . If your barcode was on the list of allowed keys, I raise output 7 on this board for 6 seconds. Input 6 (the right-hand illuminated LED) shows that the door was closed when I took this picture. See below for how I sense if the door is opened or not.

Some successful reads.

When the K8000 board raises the right output signal, this driver circuit sends 24VDC to the door strike, shown below.

In this electric strike is a solenoid that relaxes the part of the strike that was holding the door closed. The door still functions as it did before, but now I have an additional way to allow the door to open.

This is the top of the door frame, where I have wedged a reed switch into the wood. There's a magnet on top of the door that closes the switch when the door is closed (hence the turned-on LED in the picture above).

Closeup of the reed switch in the wood.