# Making a parallel Port LPT out Transistor interface Cool and fun project

#### CyBerE3

Joined Jan 12, 2011
1
This is a circuit I dreamed up in my head. I have the Schematic for it but I don't know how to post it. It is a very basic circuit. I am using the 8 LPT outputs from the parallel port on the Desktop computer to trigger 8 Transistors which in turn can control instead of 5.5 Volt accessories will be able to Control 12 Volt Accessories. What really is making this easier is the fact that the ground is the same for the LPT port as it is at the 4 Pin Molex plug and the case ground. This way I simply connect the LPT out to the Collector of the transistor through a resister and directly onto the Collector of my transistors. I am switching the ground rather than the High side or the 12 volt and now I can power up my 12 volt LEDs and use LPT effect or my other LPT control program to switch on and off either Relays or 12 volt Accessories at about 200MA. these are not very highly rated transistors and it is mostly just something to do. not a real serious project. I have the Collector pins of my transistors soldered in, but so far that is as far as I have gotten. I have a box chocked full of Capacitors, Resistors, Transistors, LEDs,etc, etc, etc that I am having to dig through and then test every component before I solder it, so that has taken most of my time. Some of the transistors have different numbers on them like a 2N3906 B331 and a 2N4403 331 but that is mostly determining how much current they can handle and that sort of thing. They should be more than capable of handling the small amount I am putting on them. and once I get this finished I will make a video and post it from my Youtube so you all can see how it turns out. I am not going to make a video of the making though because I have a lot on my mind. By the way all of the transistors passed the Touch test I gave them and all in the same direction. my touch test is simple. I hook up an LED on a resistor, face them the same direction and if I touch the collector pin and the base pin and the LED lights up.. this to me means that it is the same type of transistor as the others and that it works. I didn't care to look up the part numbers and I am using jumbled Transistor types because I am being lazy lol, it should work though.

I'm Having some fun wish me luck!

#### CDRIVE

Joined Jul 1, 2008
2,219
OK,... good luck.

#### CDRIVE

Joined Jul 1, 2008
2,219
Whoops, I'm sorry. To attach a schematic; just click "Manage Attachments", "Browse", and navigate to your schematic, click "Open", wait for it to appear in the panel and then click "Upload".

#### eblc1388

Joined Nov 28, 2008
1,542
This way I simply connect the LPT out to the Collector of the transistor through a resister and directly onto the Collector of my transistors....
I'm Having some fun wish me luck!
Do you mean BASE instead of Collector?

If you mess around with the LPT port without using the proper buffer circuit(e.g. ULN2003A), you will risk damaging the I/O chip on the motherboard and it could render the motherboard useless in some case. The damage is usually not repairable or not worth repairing.

There are so many reported incidents of blown LPT ports on motherboard. Don't add to the statistic.

#### CDRIVE

Joined Jul 1, 2008
2,219
Do you mean BASE instead of Collector?

If you mess around with the LPT port without using the proper buffer circuit(e.g. ULN2003A), you will risk damaging the I/O chip on the motherboard and it could render the motherboard useless in some case. The damage is usually not repairable or not worth repairing.

There are so many reported incidents of blown LPT ports on motherboard. Don't add to the statistic.
Now this is some good advice.

#### thatoneguy

Joined Feb 19, 2009
6,359
While on the topic, you should write to the windows interface for the parallel port, rather than directly to 0x3F8 or whatever your port address is.

To do "bit banging" I/O on the parallel port is difficult when using a USB -> Parallel port converters, and most new systems do not come with a parallel port, only extra USB ports in the LP Port's place. Your next project should be a "USB Breakout Port", which can control a huge number of outputs, although possible, they can often be purchased for less that it costs to build one though.

What you are making is a Parallel Breakout Board That link has one with transistors for diving CNC equpiment.

#### CDRIVE

Joined Jul 1, 2008
2,219
To do "bit banging" I/O on the parallel port is difficult when using a USB -> Parallel port converters,
Yeah, USB/Parallel converters are not the same animal as a USB/Serial converter which, for the most part, are invisible to the app accessing the virtual Serial Port. USB/Parallel converters are useful for use with ParPort printers and devices listed by the manufacturer. In VB there is no way of sending Hex commands to them as would normally be done through these .dlls to the ParPort. Doubtful that other languages would have an easier time of it either. At least without a manufacturers SDK, that is.
Rich (BB code):
Public Declare Function Inp Lib "inpout32.dll" Alias "Inp32" _
(ByVal PortAddress As Integer) As Integer

Public Declare Sub Out Lib "inpout32.dll" Alias "Out32" _
(ByVal PortAddress As Integer, ByVal Value As Integer

#### CDRIVE

Joined Jul 1, 2008
2,219
http://campbelldesigns.net/breakout-board.php
and all can say is one look at that board and it becomes very apparent why Serial data replaced Parallel data and very quickly. That said, I still use an old 1998 Cannon 250 printer on LPT.

#### thatoneguy

Joined Feb 19, 2009
6,359
http://campbelldesigns.net/breakout-board.php
and all can say is one look at that board and it becomes very apparent why Serial data replaced Parallel data and very quickly. That said, I still use an old 1998 Cannon 250 printer on LPT.
Remember where Parallel ports were "Fast" and serial was "Slow"? Back when serial typically ran at roughly 2400-9600 baud, parallel ports COULD move more data. Now that serial is moving in the Megabit range, the LPT has been left in the dust.

#### CDRIVE

Joined Jul 1, 2008
2,219
Remember where Parallel ports were "Fast" and serial was "Slow"? Back when serial typically ran at roughly 2400-9600 baud, parallel ports COULD move more data. Now that serial is moving in the Megabit range, the LPT has been left in the dust.
Yes I do but RS232 is still popular in industrial control because it's more than fast enough for the relatively small amounts of data being transfered. They also handle much longer runs than LPT.