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[Lcdproc] need help ID'ing a Samsung 20x4 LCD

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  • From: joris AT (Joris Robijn)
  • Subject: [Lcdproc] need help ID'ing a Samsung 20x4 LCD
  • Date: Wed Sep 15 19:10:01 2004

On 15 Sep 2004 at 13:52, Derek Stark wrote:

> Hey guys:
> I've got a Samsung 20x4 LCD panel (KS0066 controller) that I purchased
> about 2 years ago from BGMicro. I'm finallly getting around to doing
> something with it and I'm trying to figure out the backlight....
> There are 14 points across the top edge (I can only assume for the LPT
> connection & LCD power), and then there are two larger solder points on
> the left side (when looking at the back of the LCD). I'm assuming the two
> fattys are for the backlight. There are no markings on these two
> whatsoever that might indicate the polarity, and proper voltage is even
> MORE of a guess.

These pads are usually directly connected to the leds in the backlight.
Often two leds are placed in series and several of these in parallel. You
will at least need a resistor in series with the leds. The values depends
on your display. You could try to connect the pads to 5V WITH A RESISTOR
of about 100ohm. The backlight will probably light a little bit. Measure
the voltage over the led connection while lighting. The current is now
quite low and undangerous, the voltage will probably be 10% higher if the
leds light properly. Now, calculate the proper resistor as follows:

Vsupply - Vleds
R = -----------------

So this could be:

5V - 3.4V
R = ------------ = 16 ohm
100mA <--- (remember 1mA is 1/1000 A)

The power requirements of the resistor become higher with current:

P = Vsupply - Vleds * Ileds

In the example:

P = 1.6 * 100mA = 0.16 W

Usual resistors are 0.25W so in this example they could be used. If you
use resistors with a too low power value they will start smoking...

I hope this helps.


Joris Robijn
<joris AT>
Mobile: +31 6 288 41 964

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