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 .
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
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.