sonaiko

Hi..
yes i need a very simple request...
Now i theoritically understood the parallel port of the PC and how it works. i still need a practical example so i can see if i really understood it.
what i want is a simple example. Like i want to connect 8 LEDs to the port and just turn them ON and OFF by sending the binary data through the parallel port...
im using windows XP...
what things should i do...
I KNOW NOTHING.. ABSOLUTLY NOTHING...
what r the components i need?
the parallel port is a female connecter.. how can i connect the LEDs to it?
what r the values of the resistors i should use?
is the prallel port current that is sent enough to turn them on?
do i need an external votlage source?
how should i connect the LEDs to the parallel port?
what code should i use to do that? ( i know C/C++/VB )
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plz help me..
if anyone knows links wer i can find all the infos.. plz tell me..

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williB

well others know how to use VB and the parallel port.. i saw somwhere that there is a VB source code to do that..
yes i would use a seperate 5V powersupply..
i would also use a 74LS373 ic to turn your LEDs on and off
the 373 is an octal D type latch which is just eight flip flops..
i havnt looked at the signals for the parallel port in a while but you could use the Enable (pin 11) to get the data into the 373 and thus light your LEDs..

williB

yes the strobe is active low so you will also need a 74LS04 inverter to invert the STROBE signal fron the port..
all this means is.. when the strobe signal on the parallel port is low the data is available at the parallel port.
and if you connect the strobe to the inverter input , connect the inverter output to the Enable pin on the 373 .. the 373 will latch the data on the parallel port.

jrz126

I'm assuming the 373 is for protection of the parallel port. Why not just use a simple transistor array to do this? (ULN2803 would work great for this) This way just the 8 data pins can be used.
I have a decent VB program at home that I used, I believe it was called portio95.zip, this worked pretty good. I'll upload it when I get home from school/work.

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Jeff Zimmerman
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

williB

with the transistor array , they might blink ,if you send them a lot of data , but with the 373 you can turn them on and off.

jbeng

Here's the circuit I have used many times to interface to the parallel port. It uses the 74HC573 instead of the '373. The two chips work the same, but on the '573, all the inputs are on one side of the chip with the corresponding output directly across from it, I find it more convenient. You would probably need current limiting resistors (330 ohms or so) on the outputs of the '573 in series with the LED's. I've never had a problems by just hooking the LED's directly to the '573 outputs though. Connect +5vdc power to the '573 (pin 20) and the '04 (pin 14). Connect gnd to pin 10 of the '573 and pin 7 of the '04. Also, connect +5vdc to pins 3, 5, 9, 11 & 13 of the '04 to keep them from floating and doing weird stuff.
Have fun & good luck!
JB

Attached Images

p_port_latch.gif (5.5 KB, 313 views)

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