Joy Yokley - Coverted document from Linuxdoc to DocBook v4.1 (SGML).
Many people asked me, "Is it possible to control some electrical stuff [e.g. lights, radio, tv, etc.] by using a home computer?" The answer is YES. The process is very easy, and anyone can do it.
After I read the Coffee Machine Mini-HOWTO, I got an idea of how to control my home electrical appliances. I made some modifications on the circuit discussed in that Coffee Machine Mini-HOWTO, and wrote a simple program. The circuit can control many small electrical devices.^_^ You can use crontab to set your lights to come on automatically or to turn on your airconditioner. I use it to control my VCR and VCD ( I do still need some modification on VCR/VCD). By writing a simple program, you can control everything over the web. You can use telnet with SSH and your telephone dial in to control all the appliances you have on the circuit.
This circuit is VERY SIMPLE. Even if you don't know anything about circuits, you can set up this circuit.
Get any computer that is running Linux and has a working parallel port. :) I'm using a 386DX with 4MB RAM 40MB HD. You will need gcc to compile the program. If you want to use telnet or SSH, you will also need telnetd or sshd. You can write your own program by using ioperm and outb. If you would like to use my program, you will need g++.
Click the following link to download my program. You will need g++ to compile it. edc.sourceforge.net/paralle.tar.gz.
The data line of the parallel port can provide between 0 and 5 volts. Therefore, we can use this line to control a relay and let that relay control an electrical device.
Use pins 2 through 9 to get +5V
Use pins 18 through 25 as the Ground
Below is the key to the diagram above:
+5 volts from parallel port will turn on the relay. Once the relay is on, the device connected to that relay will be on. When the parallel port's data line goes back to 0, it will turn off the relay, and device is off.
The diagrams below are used to explain how relays work.
The relay itself is just a switch as seen in the diagram below:
The diagram below demonstrates the setup of a 4 pin relay.
In the diagram above, pin 3 and pin 4 are disconnected by default. When you send +12V between pin 1 and pin 2, it will turn on a switch, and pin 3 and 4 are now connected.
The following is a 5 pin relay:
In the above diagram pin 3 is connected to pin 5, by default. By sending +12V between pin 1 and pin 2, you will will turn on a switch. Pin 1 and pin 2 will disconnect, and pin 5 and pin 4 will connect.
Some relays may have more that 5 pins. More pins just means there are more switches.
I wrote a simple program that can control 8 relays. The program is available at the following location and will need g++ in order to be able to use this program. http://edc.sourceforge.net/paralle.tar.gz
A complete circuit can control up to eight relays, that means that a complete circuit can control eight different devices. You will need a DB25 connector. Using a parallel switch cable, connect this relay board to your computer. I put the relay board in a box and use a parallel switch cable to connect it to my Linux box:
Below is an example of how a relay board would connect with your electrical device:
To connect the system, just connect your home electrical device to the power outlet. That is it! You don't need to make any change on the electrical device. And you can connect any kind of device to that power outlet. Plug this power outlet into any wall outlet.
To see photos of what the finished product looks like, go to the following sites:
The following URL shows a complete electronic circuit (control 8 devices): http://edc.sourceforge.net/01.png
Special thanks to Rufus Chang firstname.lastname@example.org.
Special thanks to Chih-Wei Huang email@example.com.