advice needed on variable resistors for LCD

asteroid · 10-04-2001, 07:43 AM

With that diagram everyone has for coupling LCD screens to printer ports;

I notice there are two variable resistors needed for the brightness and contrast of the screen.

1/ I dont know too much about electronics but I've built by own cables before, could anyone tell me what exact parts I need, ie: any particular wattage or type these variable resistors need to be. So I dont feel stoopid walking into Maplins explaining what I need for my project.

I am going to order some $15 non backlit 4x40s from EIO

John H
http://mp3appliance.ohgo.com

helloman · 10-04-2001, 09:12 AM

Use POT ... and connect it to pin 1, 2, 3. in between cable and 4x40 LCD..

then you can adjust Resistor value using Pot.

I used 100k (104, I think) and works fine..
but not that broad range.. I had this so I just used for change brightness...

You might try less pot resistor..

[ 10-04-2001: Message edited by: helloman ]

SuperMatty · 10-16-2001, 12:46 AM

I wondered this myself at one time. I have Timeline's 40x4 Densitron backlit LCD display, and I found on the Densitron website that they recommend a 2.3 ohm resistor for the backlight. So, instead of trying to find a 100 ohm potentiometer, I simply wired 2 1-ohm resistors in series and as far as the contrast potentiometer, well, I find there is no need for it, as full contrast is the best for my particular display. So I have that connected directly to ground. LCD is beautiful and the brightness is as bright as it could possibly be without getting hot.