A simple LCD question

kirkabus[tdo] · Post by **kirkabus[tdo]** » Tue Sep 11, 2001 4:47 am

Hi, does any body know if the LCD's sold by matrix orbital are backlit with LED's?

If the LK202-25-V uses LED's how hard would it be to chaneg them to blue?

Post by **Henry** » Tue Sep 11, 2001 9:40 am

Good Morning...

Yes the LK202-25 is a LED backlit display.

as you can see the LEDs inside the backlight are surface mount and inbeded inside a thick layer is some kind of plastic. I tried taking some out but had no sucess. They only thing I can thing of it taking out the backlight and replacing it with a side firing blue LED. But the glass is green on the LCD as well, so it will not look right.

_________________
Henry J.
Technical Support
Matrix Orbital

<font size=-1>[ This Message was edited by: Henry on 2001-09-11 09:41 ]</font>

PatO · Post by **PatO** » Fri Nov 02, 2001 6:36 pm

Henry,
I'm assuming you(MO) order the LCD parts from some manufacturer over the rainbow and through the woods...
Would it be possible to do a special order of a quantity of displays with different colored LED's and LCD's? Perhaps we could rally the masses and put some money down for an order?

-or-

If you(MO) build the displays from scratch... Could I send you a packet of LEDs I bought at Radio Shack and have them installed in a display?

Post by **Cheese** » Mon Dec 17, 2001 4:22 pm

this LCD of mine (glk 12232-25) is lit by just one led which is side mounted - very easy to change! Unfortunately it's not as bright as the led array ones but it still looks very nice

Cheers,

r.

Post by **Henry** » Mon Dec 17, 2001 11:25 pm

There was some talk about trying to change a LK204-25-PC one, it's side firing as well. So if you cut it off and replace it with a different color and glue it back, you might be able to do it... (BTW, this WILL void your warranty)

Polarsmurf · Post by **Polarsmurf** » Tue Dec 18, 2001 3:12 am

yea i looked into changing the lighting, but never found 12v leds, and i've forgotten how to wire it up to use 5v instead.. (if only i didn't sleep during HS physics.)

Post by **Cheese** » Tue Dec 18, 2001 3:18 am

You sure the led in your mo display is a 12v one? Anyway a 470 ohm resistor will let you put a 5v led on a 12v line... cheers,

r.

Post by **Henry** » Tue Dec 18, 2001 9:39 am

On 2001-12-18 03:18, TheCheeseMan wrote:
You sure the led in your mo display is a 12v one? Anyway a 470 ohm resistor will let you put a 5v led on a 12v line... cheers,

r.

The LK204-25-PC uses 12V LEDs and everything else uses 5V...

jodynicH · Post by **jodynicH** » Wed Dec 19, 2001 10:48 am

Henry- make us some of those plastic led mounts for the 204-25PC with different color leds and sell those as options. Hehe, that would rock

ChriX · Post by **ChriX** » Wed Dec 19, 2001 2:37 pm

Yeah, ive got one of those backlights at home, I ripped it out of this other, inferior LCD that I blew up. Trying to think of something to do with it.

Post by **Aniso** » Thu Dec 20, 2001 7:18 pm

I don't stop by here as often as I should, but please take this as the "VOICE OF GOD" (rumble) (rumble)

LEDs are neither "5 volt" or "12 volt". The only specification a LED has (in terms of requirement) is current.

As a characteristic, LEDs also exhibit a "forward voltage drop". First, it might be useful to say that the "D" in LED stands for Diode. A silicon diode has an inherent forward voltage drop of 0.7 volts. A classic LED's forward voltage drop is isually about 2 volts and it's current requirement is about 20mA. The new super bright blue and "white" LED's usually have a forward voltage drop of around 3.5 volts and a current requirement of around 30mA to 40mA.

Lets do some math.

Say you have a 5 volt supply. All the voltages of all the loads in the series circuit will always add up to what the source voltage is. Obvious, but it has a name anyway - Kirchov's voltage law (or is that Kirchoff?) So far, we have a voltage drop of 2 volts across the diode, so we have to account for an additional 3 volts (if it were a 12 volt suppy, you would have to account for 9). You want a current of 20mA, so by Ohm's law (V=IR), R = 3/0.02 = 150 Ohms. This is the resistor you need in this series circuit to keep the LED from blowing up. Similar calculations for 12 volt supplies and Blue LEDs. Look up the specs!!!

One little note about this. Blue LEDs with the large forward voltage drop make the value of the "current limiting" resister fairly critical. Because there is only 1.5 volts of overhead, a small difference in resistance can mean a large percentage difference in current. This is one of the reasons that the Matrix Orbital LK204-25-PC supplies the backlight from 12 volts. It is just easier to control without getting paranoid about resister tolerances.

I have spoken (rumble) (rumble) LOL

--------------------------------------------
P.S. Henry, why are you always talking about "cutting off and gluing"? Can't you just pull out the LEDs or break them out?
_________________
anis- or aniso- combining form [NL, fr. Gk, fr. anisos, fr. a- + isos equal]
: unequal <anisotropic>

<font size=-1>[ This Message was edited by: Aniso on 2001-12-21 12:27 ]</font>

Post by **linear** » Fri Dec 21, 2001 8:47 am

I typed a 600-word expansion of Aniso's response, and the board ate it because I entered the wrong password.

Post by **Aniso** » Fri Dec 21, 2001 12:24 pm

Man, I hate it when that happens. On my machine, using Opera 6, I can safely "Back" after that and the message is still there, but I am still paranoid and almost always copy the text before I hit post on any board I am on.

BTW, Opera 6 rocks, though it's hard to decide which is worse - Microsoft or Norwegians...

Post by **Henry** » Fri Dec 21, 2001 12:51 pm

On 2001-12-21 12:24, Aniso wrote:
Man, I hate it when that happens. On my machine, using Opera 6, I can safely "Back" after that and the message is still there, but I am still paranoid and almost always copy the text before I hit post on any board I am on.

I have dont that so many times, one night I most have written the same thing 6 times... now I just copy and paste to be safe

Polarsmurf · Post by **Polarsmurf** » Sun Dec 23, 2001 4:47 am

470 ohm resistor? and your sure of this? I might just do this because i think i slightly blew one of my LED's, kinda dark on part of the lcd. Who knows, time to find 5v flat red leds. Btw, anyone got the size of those things across?