LED Display using parallel ports

[m_ocx]

hi,
iv made a simple led using 8 led's, and im be able to control it using vc++.
i directly connected each lights to 2-9 pin and other to 25 (ground).

my question is , if i want to make a big display with LED like 100X100 (and i dont want to use LCD) , whats the solution ? how i must send signals to address one LED for example LED 50,54

 

[Nigel Goodwin]

hi,
iv made a simple led using 8 led's, and im be able to control it using vc++.
i directly connected each lights to 2-9 pin and other to 25 (ground).

my question is , if i want to make a big display with LED like 100X100 (and i dont want to use LCD) , whats the solution ? how i must send signals to address one LED for example LED 50,54

It's called multiplexing, and requires you to switch rapidly between different rows and columns, relying on persistance of vision to give a complete display to the viewer.

100x100 is a seriously large display, you would need 200 I/O lines and associated drivers - not to mention the cost of 10,000 LED's!.

I would suggest the preferred way to make a display that large would be to split it into smaller sections, each with it's own microprocessor.

 

[m_ocx]

thanks for your answer,

i said 100X100 because im looking for a main way to making big structures of switches,
lets try a 40X40 display,
you said something about multiplexing,

can you give me an example , or something that i can start from ?

 

[Nigel Goodwin]

thanks for your answer,

i said 100X100 because im looking for a main way to making big structures of switches,
lets try a 40X40 display,
you said something about multiplexing,

can you give me an example , or something that i can start from ?

Have a look at my keypad PIC tutorial, it uses a multiplexed 4x4 HEX keypad - exactly the same method is used for larger ones (including the keyboard you are probably typing on now).

 

[Electric Rain]

Nice self advertising Nigel. :lol: j/k

Anyway, you have eight outputs using your parallel port... so, if you only were using a 4x4 display of LEDs, this would be VERY easy. This way, you could matrix the LEDs... but you're using 10 times that many... hmm... well, I'll think about it, because an EASY way to do this bugs me now. I'll try to come up with something, but don't hold me to anything, because I might not be posting again here. :lol: That's all I know how to do is matrixing, so I hope that helps you in some way. :wink:

Rain

 

[m_ocx]

could anyone please give me an example ?!

about 4x4 matrix you mean something like this

5 x x x x
6 x x x x
7 x x x x
8 x x x x
#1 2 3 4

if i want to turn on (1,8 ) i must turn on this signals (1+128=129) ?!
how is Circuits then ?!

 

[Nigel Goodwin]

could anyone please give me an example ?!

about 4x4 matrix you mean something like this

5 x x x x
6 x x x x
7 x x x x
8 x x x x
1 2 3 4

if i want to turn on (1,8) i must turn on this signals (1+128=129) ?!
how is Circuits then ?!

No, you must take one high and one low, so to light ( 1, 8 ) you could have pin 8 low and all the others high, or pin 8 high and all the others low (depending on the design).

 

[maheshsb04]

hi,
iv made a simple led using 8 led's, and im be able to control it using vc++.
i directly connected each lights to 2-9 pin and other to 25 (ground).

my question is , if i want to make a big display with LED like 100X100 (and i dont want to use LCD) , whats the solution ? how i must send signals to address one LED for example LED 50,54

:lol: **broken link removed**

 

[m_ocx]

Realy i'm beginner in electronics,
can you please give me an example of cirtuits ?

 

[Electric Rain]

Ok, I just drew this up. It's not quite right though. I gives you the basic idea, but I'm pretty sure you need to add some resistors. I'm not quite sure where and I don't know of what value. Can someone else please tell me where the resistors should go and what value they should be so I can draw them into the schematic for m_ocx?

Also, this schematic is correct (minus the lack of resistors) right?

 

[m_ocx]

oh realy thanks
this is exactly what i was looking for,
now about adding more LED's and developing bigger matrix what we have to do ?

 

[Nigel Goodwin]

oh realy thanks
this is exactly what i was looking for,
now about adding more LED's and developing bigger matrix what we have to do ?

Bear in mind that each LED must have a series resistor to limit the current, otherwise you will probably blow both the LED's and the parallel port!.

To add more it gets MUCH more complicated, you have to create a lot more output pins - you can do this by using shift registers - but both the hardware and the software get rapidly more difficult!. The 100x100 design you mentioned would be very complicated (and expensive), and I'm not sure how fast you would be able to multiplex it - too slow and you see the visible flicker.

 

[Electric Rain]

Bear in mind that each LED must have a series resistor to limit the current, otherwise you will probably blow both the LED's and the parallel port!.

Yes this is true, that's what I was saying but what should the value be? 330ohms seems like a familiar value...

To add more it gets MUCH more complicated, you have to create a lot more output pins - you can do this by using shift registers - but both the hardware and the software get rapidly more difficult!. The 100x100 design you mentioned would be very complicated (and expensive), and I'm not sure how fast you would be able to multiplex it - too slow and you see the visible flicker.

This is true also. Again... I'll try to think of some way to do this other than multiplexing, but for now, all I can come up with is this 4X4 display by matrixing. Sorry!