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If you are just starting out with parallel port interfacing like i am, you will need some way of checking your work. There is other ways to check the port such as DMM, but that only checks one port at a time. After much frustration i decided i needed a better way. 

You will see this called by several different names. D25, parallel port, printer port maybe more but they are all the same thing.

I used this LED calculator  http://led.linear1.org/1led.wiz to determine the correct resistors to use. The ports are 5v.

So in the alculator i used:
source voltage - 5v
diode forward voltage - 1.4
diode forward current (mA - .25

This gives us 150 Ohms.

I next used alternating green and yellow LED's and soldered them to the sub D-25 connector.
The D-25 connector pins have more than one number assigned to each pin. Can get confusing. We will be using numbers 1 - 25.    The actual main ones we will bu using are pins 2 to 9 ( also numbered D1 to D8 ) and 18 to 25 .
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We will soldier the anode( positive longer end ) end of the LED' s to pin 2 through pin 9.  Then we will soldier the resistors to grounds. Pins 18 through pin 25. That gives us 8 pos and 8 neg connections. Next we will soldier the  cathode ( negative shorter leg )  to the resistor.  Try to line each one up each resistor to its respective LED the best you can. If not aligned very well its ok , you can adjust after they are soldiered.    

Step 1: SoftWare

This is a screen shot of the program i am using, Lalim Parallel Port Control Basic. Version 3.6.0. The Last update on the program was November 2009. So support is no longer available.
I think they have a pay version now.
Even the down load sites no longer have the program available for down load. I don't remember where i got it, but i just happened across it while searching the web. Altho you may be able to find it somewhere, not sure.

I have it available for down load on this ible.

There is alot of options on this program. I have only just looked through it. I use it only manualy for switching the lighting and exhaust fan in my house.
That will be a different Instructable.

Step 2: Bios & LPT Com Port Settings

If  you can not get any readings from D25, parallel port  you may need to check the setting in Bios.  To do that you need to, restart your pc and while it is booting continually press delete until the Bios screen comes up. The mouse no longer works in Bios so it will all be done with the keyboard.

Scroll down to Integrated peripherals, hit enter. Scroll to I/O devices, hit enter. Check if Parallel port 378 is selected. If not select or enable.
Now Mode options. Normal is more for out communications. This is the slowest of any options. But most reliable. ECP is next fastest and can be used without any supporting programs, well integrated. Next is EPP, this is the faster data transfer your PC has. It also can have some problems with communications. My need supporting programs to run. You can choose this and try it, if you have problems with data transfer you will need to choose a different option. Last there is ECP & EPP. If you choose this your PC is supposed to determine what one is optimal to run, automatically. I never have tried this, i suppose it works the way it says.
If you dont know or are not sure set it to NORMAL.
Lastly press ESC until you are at the original first screen. Press F10 to save and exit. Hit enter and your pc will reboot.
I dont think a person could tell the difference in the speeds if they are using the port for general use, triggering LED's, sending signals for a CNC ect. The only time the fastest setting will really be needed is if you are transferring massive amounts of data. The the only 2 practilcal choices in my opinion is either NORMAL or ECP. These settings are for MSI 41 series Main boards. Every manufacture does there a little bit differently.
 Look in the device manager, click on ports. Make sure the printer port  LPT1 is there and does not have a yellow question mark on it. If no GOOD! On way to open the device manager is click start then control panel then administrative tools then computer management  then device manager and finally the plus sign at Ports. 

This is a pic of my relay board that is switched by the Lalim program. Controls 3 lights and 1 exhaust fan. I have 4 more ports available that are not in use yet.

One more important thing is there should be a port buffer to protect your pc from damage. I will try and post an ible on one, or search for buffer board and you can find them on here. 
I thought this is so cool! I like the idea of having LED's connected up and sending some data down the line just to watch them blink...........I know, it's really for checking the port....just a thought, maybe a disco....I must be getting old. :)
Thanks. <br>I will leave the disco lights for you. <br>I like your PCB holder. I had wanted to make one like it from your design but for what ever reason i never got much of a start.
Too many projects and not enough time....plus implementing your own creations......

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Bio: Why would i buy something ready made when i can make it myself with half the features for twice the money? DIY!
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