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In the mid 80's there was the Intel 8052-BASIC chip. It had a decent integer BASIC with serial interactive I/O and could, with the proper 21(ish) VDC, burn EPROMs. I designed and manufactured a COCOT payphone using it. Quite the fun thing to play with.

Using a Dallas Smartsocket JEDIC socket with a 6564 SRAM chip made a great development environment.

This was back in the mid-80s. This has better speed and Ethernet, but for the decades that have past, not anything astoundingly new.

You can answer this question in 5 seconds on Amazon or Google... Axelson wrote a book on USB development as well. Check it out here

$ java net.sourceforge.pmd.PMD ~/tmp/eec/embedded_ethernet_complete_code/ text rulesets/unusedcode.xml -shortnames

Tini/RealTimeWebPage/RealTimeWebPag e.java 42 Avoid unused local variables such as 'server'
Tini/SendEmailMailto/SendEmail.java&nbsp ; 106 Avoid unused local variables such as 'mySendEmail'
Tini/TcpServer/TcpServer.java 35 Avoid unused local variables such as 'myTcpServer'
Tini/UdpReceive/UdpReceive.java 31 Avoid unused local variables such as 'myUdpReceive'
Tini/UdpSend/UdpSend.java 43 Avoid unused local variables such as 'myUdpSend'

Yeah, Byte magazine used to kick ass. I remember when they used to carry hardware hacking articles and print PCB solder side masks.

Computercraft/Microcomputer Journal used to be a good one too before they went belly up. Jan Axelson's articles were great.

I don't know of any current magazines that are like those two were.

I did this once. A cheap radio shack photocell tied to +5 volts via an active output pin on your parallel port, with the other end of the photocell going to an input pin on that same port, will cause that input pin to read 0 when little or no ambient lighting is present. When hit by a red laser pointer the resistance across the photocell is lowered and the voltage at the input pin ramps up above the binary threshold, to more than ~0.8 volt but less than 5 volts. Because of this, reading the input pin from software when the photocell is lit by a laser beam shows a binary value of 1. To avoid false alarms from stray light, I housed the photocell in a sealed, opaque box with a hole in it for the laser beam to enter and hit the photocell.

A simple C program that reads and writes the memory address of the parallel port can detect, log, and act on these "laser trip" events, doing something as simple as beeping, or as complex as taking a picture and asking for a code. The program should write a 1 to the bit that controls the output pin you are using so that +5 volts appears on it. It should then repeatedly read the input pin you are using. When the input pin transitions from 1 to 0, even for a moment, you know the laser beam has been cut.

The quick and dirty C code to do parallel port operations under linux can be found at here. For beginners I suggest you use one of control bits/pins as your output and one of the status bits/pins as your input. The data bits/pins are bi-directional and must be configured for input or output, and using them makes things slightly more complicated. If you want to get really fancy try using the parallel port IRQ to detect the transition from 1 to 0, this should save processing power by avoiding an expensive loop to check the state of the input pin constantly.

If you need a little more background on the parallel port before diving in, check out this resource

Finally, the above description is for a single laser beam. I used a mirror to bounce a single beam around, to get greater coverage, and to provide the effect of multiple beams in the presence of aerosol or powder. You should be able to support thirteen independent laser beams on a single parallel port, using the data bits/pins and the status bits/pins combined.

Win 9x has direct access to the ports. Win NT/XP needs you to go via the device drivers, but it's not a difficult problem - plenty of info for how to do it.

Beyond Logic
Parallel Port Central

Both the above have a bunch of useful stuff.

Also don't forget that you'll need to learn how to drive LEDs. I'm admin on an electronics board, so here's a blatant plug:-

BasicElectronics board, LED FAQ

(and kudos to David Bridgen and MacGregor who put that info together :-)

Grab.

ActiveWire has a nice looking USB project board, and a number of add-on boards that will probably do what you want, with Linux and Windows drivers. USB Central is a good USB resource page with links to that and other USB boards.

That reminds me of a very cool clock I saw in Hong Kong (of all places ;)

It had a single row of LEDs, mounted along a pendulum. The pendulum would swing back and forth, and the LEDs would flash so as to make it look like the current time was 'hanging' in the air in front of you.

Kind of like the way monitors work, I guess, except with a very low refresh rate.

You can rig one up with your parallel port (I think parallel ports can just put out enough current to drive LEDs, but you might blow your port outputs if you're not careful); get it to output a fixed sequence at a certain frequency and wave a bit of wood with your LEDs mounted on it back and forth, and you should see a nice pattern.

I had a friend who was doing this, but I have no idea if he got it going or not.

Toner transfer is my method of choice. I stuck transparencies, like you'd use in an overhead projector, into my laser printer. I crank up the darkness of the page, so it puts a lot of toner onto the transparency.
Then, I print my board layout, in mirror image, onto the transparency. Rest it on the blank, clean copper-clad board, and run a hot steam iron over it for a few minutes. With some practice, you'll be able to transfer enough of the toner onto the board that when you etch the blank board, your layout comes through.

• http://www.ping.be/~ping0751/thepcb.htm - *The* PCB FAQ. Extremely informative.
• http://www.lvr.com/pcbs.htm - Jan Axelson's PCB page. I bought her book a long time ago and found it quite useful.