This made me realise that alot of new Motherboards arnt coming with LPT support. Amazing to think that just 10 years ago i had a daisy chain of those things for various Printers and Scanners. Even an Early digital camera connected to my computer through the LPT.

Nice writeup. But a word of caution from someone who has fried a motherboard or two, with a little mistake interfacing on the LPT port with a setup very similar to the writeup… Nothing beats opto isolation in my mind.

@ mrgoogfan, you are correct that many don’t come on the back panel, but a header is usually available to add one.

Besides the fact that older PC’s are everywhere for dirt-cheap.

Check out this software if you want to play with a parallel port:

http://neil.fraser.name/software/lpt/

For those of us who haven’t seen a LPT port in years, go dig out your old server and desolder the ISA connector and scavenge the ISA printer port card, You can use the SCSI ribbon cable to make the connections. Then make a USB to LPT adapter and Bob’s your uncle.

Alternatively, buy a $15 FTDI usb cable and shove an AVR in the end of it.

@Pete: Or use the free V-USB. In fact, the first “getting started” demo for V-USB is an eight-bit output port for switching devices on and off using your PC – http://www.obdev.at/products/vusb/powerswitch.html :-)

Ok, using an arduino and using a microcontroller are not mutually exclusive.

All microcontrollers are not Arduinos, and all microcontrollers are not considerable overkill for most projects like the arduino.

There is no problem using a PIC or ATMega/ATTiny or something for your project, as long as you build something within the scope of your project and know how it actually works.

A tweeting plant waterer with full TCP/IP service and ethernet? Ok, that might need an Arduino. A LED driver to RGB mix a few LEDs? Gimme a break, you can do that without a uC at all and you certainly don’t need what is in effect a small pre-built computer to do it for you.

Also, it’s a Parallel port. LPT is a specific software identifier which can be mapped to any number of ports of several different types.

Analyzing the rs232, needing precise timings, capturing the rs232 byte packet, plus it’s time characteristics, to find out why something is not working is still more complicated than looking at the debugging LED’s light up on a parallel port, as you step through your program one instruction at a time. Unfortunately the minimum pincount of an LPT is 8 pins for 1 byte at a time, plus some ack line for hardware clock transfer. But 9 pins and wires are a lot easier to solder/crimp than 25. But usb to dumb 9 pin is impossible, because USB only has only 4 wires, and 2 of those are power, but USB to dumb serial, and dumb serial to intelligent 9pin parallel could be possible via something as cheap and simple as a shift register right inside the 9pin connector, without drivers, directly in hardware of USB, bios configurable as either a driverless dumb RS232 or driverless realtime LPT port.

@slincolne “but NOT the USB adapter version”

What is the cheapest USB to digital IO that is avaialable off the shelf and immediately usable?

There are plenty of very cheap USB to RS232 or USB to LPT cables… The question is which ones have the ability to read and write to pins?

It would be great to find a $5 cable that anybody could buy, that was easily controlled digitally from either Windows or Linux. (An Arduino does this, but is expensive overkill if you only need a few digital IO, and we can make our own cheap and easy solutions, but that isn’t an off-the-shelf solution for the masses.)

Unfortunately the reality of the parallel port is much harsher than stated here, often you’ll find ports that are not standards compliant, have no input mode setting in the bios or are just plain broken or crap. So if you’re going to use parallel in your next project, test your intended computer’s port before you invest any time.

@robocat “There are plenty of very cheap USB to RS232 or USB to LPT cables… The question is which ones have the ability to read and write to pins?”

I recently bought a $3 usb->rs232 adapter from dealextreme. It uses a pl2303 chip, so just works under linux. I was also surprised to find all control lines (rts, dtr, dcd etc) are properly hooked up. If you’re not trying to bitbang time critical protocols but just turn a couple of relays on/off I think that should work. Pretty easy to interface through something like pyserial too.

It’s not just that hardware parallel ports aren’t available any more. There’s no point to them; Windows doesn’t let you anywhere near the hardware, and Windows isn’t suitable for timing critical applications anyway. (Yeah, I know, Linux. Tell it to my customers.)

Jimmy, yes the express card parallel port works just fine ‘n’ dandy.
My understanding is that these exist because people need them for CNC machines which use the parallel port.

With my last laptop, I wanted a way to program Xilinx stuff without shelling out a couple hundred for the official Xilinx USB platform cable.. so I picked up an express card parallel port on ebay for about 60 bucks and it worked like a charm.
I had read around that the USB-parallel would not work since they were designed strictly for printers and not made to be full featured.

However it’s kind of overkill for hobby stuff. Like everybody in this thread has been saying, for much less money you can get an FTDI chip cable and an AVR, no need for any external power supply.

Interesting discussion regarding parallel ports, seams to be a touchy subject for some.

Myself I just like the simplicity of it, I think many people would like to get some basic I/O out of their computers, and this might just (for those with a parallel port) be the most simple way to do it when you like to understand all the parts involved, the complexity is close to zero.

In our case we already had the computer (with an unused parallel port) and going mc only in this case would be programatically overkill having to implement tcp/ip and IRC on the microchip.

I find “just move on” rather curious. The Bleeding Edge makes good sense in manufacturing, but to the individual hacker the past represents a rich *resource*. Machines with parallel ports are unfashionable and a dime a dozen, but that doesn’t mean they are useless, far from it.

It may be *sexy* using an expensive laptop for bench experiments, but given the real risks to your gear it is much more sensible to use one of the many castoff old junkers like are stacked in my storeroom. They all still do what they were built for and that is normally way in excess of hacker’s needs.

It’s a damn shame it wasn’t fully bi-directional from the start, but you can still do a hell of a lot with it.