Computerize Your Room/House

Home > Circuits > Major Projects > Computerize Your Room/Home

Search:

Author	Views	Views Today	Rank	Comments
	363,549	1		122

You will first need a computer, but since your reading this, I assume that you already have that taken care of. Second, you will have to buy about 20 IC's and a very expensive ISA experimenters prototyping board. These boards cost anywhere from $16 to $45, and can be purchased from your local electronics store or from Jameco Electronics (See Where To Get Parts). They have a fairly wide selection. Buy the 8 bit version, the 16 bit varsion is not needed for this project.

Since this is a major project, it will be presented in sections, starting with the Simple Parallel Port Interface. The 8 Bit Output Card will come next, followed by the 8 Bit Input Card. All three interfaces came from the book "The Robot Builders Bonanza", by Gordan McComb.

I must also stress that this is a major project and should not be attempted unlesss you have a good understanding of electronics. If done wrong, you run the risk of not only destroying the circuit, by also destroying an expensive computer as well. Double, no, triple check your work to make absolutely sure that is free from errors before installing it in any computer.

DISCLAIMER: I am not responsible for any damages caused due to a lack of knowledge or mistakes in the circuit when building and using these projects.

Now then, with that out of the way, on to the Parallel Port Interface.

Parallel Port Interface

Description

This is about the most basic interface you will see. It uses only 3 74376's (74LS367). This interface provides 8 outputs (plus 3 address lines) and 5 inputs. This is usually enough for one room, providing you make use of some demultiplexers and the address lines. You could have up to 128 output lines using the address lines, a 74LS138 and 8 74LS154's.

Begin construction by mounting the IC sockets on the board. I used a experimenters universal solder board due to the large number of wires that must cross. If a PC board were used, you would need either a multi-layer board or many, many jumpers.

Now, solder wires along the top and bottom of the board, making all the connections between the IC sockets. Do not install the IC's yet. Assemble the cable using 26 conductor ribbon cable and a 25 pin crimp connector. You will have one conductor left over so just "peel" it off. Connect the cable to the board and wire it into the circuit. I used an 18 pin socket to make connections to the outputs and inputs on the interface easy. You could do the same if you like, or use a terminal strip.

Schematic Of The Parallel Port Interface

Parallel Port Pin-Out

Parts

You operate the interface by sending bit patterns to the printer port. BASIC, GWBASIC or QBasic are the languages of choice since most computers already have them installed (in your DOS directory). If you wish, you can download control software from my files section.

The command you use is the OUT command. The decimal address of most printer ports (assuming LPT1) is 888. Use this with the OUT like this:

OUT 888,X

X is a number from 0 to 255 that represents the binary bit pattern.

Although designed primarily to get data out of the computer, the printer port has 5 input lines (on some computers it could be less). You access these lines with the INP function. This time, however, the decimal address is 889. The syntax of the INP command is:

Y=INP(X)

Y is the variable used to store the decimal value that is returned. X is the port number, which in this case is 889.

You may also use the OUT command to send data to the address lines. Just use address 890 instead of 888. Remember that there are only 4 address lines.

8 Bit Output Card

OK. With the basic parallel port interface done, you can build the more advanced 8 Bit Output Card.

Description

This is much more complicated then the parallel port interface, mostly because of the address lines used by the computer to send data to different devices plugged into it's bus.

This interface is constructed on an IBM 8 bit prototyping board. These are available from Jameco Electronics (see Where To Get Parts).Connections are made with point to point soldering or wire wrap. Note that if you use the wire wrap method the board will require about 1/2 inch clearence on the connection side.

Use sockets for all IC's. Begin construction by first mounting the sockets. Depending on which board you buy, you might have lots or very little space. Connect the IC's together using either point to point or wire wrap. I used a 36 pin connector to facilitate connection to the back of the computer, but you can use any other method. Whatever the method, install that connector and wire it into the circuit now. You may now wire the connections to the bus (the gold contacts on the bottom of the card). If you need a reference as to what the bus connections are, check out The IBM Bus Pinout (I apologize for the poor image quality). It is a good idea to bypass power supply pins with .1uf capacitors to avoid problems with interference, power supply spikes, etc. Triple check your work before installing the circuit in any computer. The simple circuit to connect the interface to relay's is showen after the schematic.

Schematic

Parts

IC Power Pins

The power connections were left off the schematic for clarity. Here they are:

Chip	Vcc	GND
7400	14	7
7404	14	7
7430	14	7
7432	14	7
74374	20	10

Relay Driver Circuit

8 Bit Input Card

This input circuit can be built on the same board as the output circuit, and share the same bus connections. This circuit is necessary if you wish to use almost any type of remote control circuit, which will most likely require more then 5 inputs as provided by the printer port.

Description

Since this is quite similar to the output circuit, I won't go into the details again. Only the parts list and schematic will be showen, as well as the "power pins" chart.

Schematic Of The 8 Bit Input Card

CAUTION: Be sure that the signals being sent to the input card do not exceed 5 volts or fall below ground!

Parts

The power connections were left of the schematic for clarity. Here they are:

Chip	Vcc	GND
74LS00	14	7
74LS04	14	7
74LS30	14	7
74LS32	14	7
74LS224	20	10

Controlling The Input And Output Cards

Controlling the cards is straight forward, using the basic INP and OUT statements as explained in the Simple Parallel Port Interface. The only difference is the address. The address for the input card is decimal 701 while the output card is decimal 703.

Choosing The Right Computer

This is the last section of this document. Choosing the right computer is getting harder these days. Since new computers no longer come with ISA slots, that basically means you are stuck using older machines. In a way this is good since it's no great issue if you fry one. Pentium class machines are essentially junk these days and basically free. Pentium II and III machines are quickly dropping into that catagory. Just make sure that you triple check your work before installing it into any computer.

Well, thats it. For more information on programming the parallel port, see Programming The Parallel Port In QBasic or Programming The Parallel Port In Visual Basic.

If you would like to leave a comment, you can do so using the form below. Comments can be things like suggestions, successes or failures, improvements, similar circuits, error reports, an answer to a previous commenter's question, or anything in between. However if you would like to ask a question it is suggested that you use the forum instead. The forum provides a more robust environment for discussion.

Important: If you post a technical question here, there is no guarantee it will be answered. All technical questions should be posted to the forum. The owner of this site generally does not answer questions in comments.

All comments are subject to approval before they are displayed here, so your comment will not appear immediately. This is done mainly to prevent spam and other abuse. If you wish to remain anonymous, simply enter "anonymous" for your name and/or email.

Name:
Email:
Subject:
Comments:
Anti Spam Code:	Please enter the exact text shown in the image above into the box below. Browser cookies must be enabled to comment on circuits.
Privacy Policy

Back To Circuits Page | Mail Me | Search |