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need voltage for LCD

kparenteau

New member
Hello,

I have this and just having a hard time reading the data sheet. I need the voltage for the backlight. Most are 5V, just double checking. If it's not 5v and my schematic calls for 5v, do I just tie in a resistor?

Thanks
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kparenteau

New member
So.. would I need a 68 ohm reisitor off of pin 15 and a separate 68 ohm resistor off of pin 2. Both of these pins will be off of the 5v molex coming from the PSU.

Thanks again CF for the great tech help..
 

kparenteau

New member
I appoligise for being dumb with this and slap me if I am but, wouldn't the 5v pin on 2 and 15 need the resistor. The schematic is showing the ground with the resistor on it. If ground is "dead" why have a resistor on it. I thought the resistor was to be placed on the 5v line..

I bought the 68 ohm resistor and just need to know which pin to put it "inline" with.

Thanks again CF and everyone else
 

CF Tech

Administrator
The 5v on pin 2 does not go to an LED, so it does not need a resistor.

The current on pin 15 is limited by the resistor on pin 16. Might seem weird, but that is how it works.

Put the 68 ohm "inline" with pin 16 as shown and you will be safe.
 

kparenteau

New member
Worked CF... but :)

Without the 100 ohm and 10k pots it looks like having things to the max settings without the pots it looks bad..


Here is a pic of the front with the LCD on and running. At this front on angle all the LED's are on and no showing LCD smartie output.


Here is the same pic but at an angle. This is the only angle that you can see the LCD running. Notice the LCD displaying LCD smartie stuff.

This is wired using all the data lines (4,6-14)
68ohm resistor on pin (16) going to ground
(1,3,5) going to ground
(2,15) going to 5v

I do have the pots, but didn't hookup for simplicity. Also I wanted to see what I really needed for pots before adding them into the scheme. At this point what pot would I need to add into this scheme to see the LCD straight on. Would I need the contrast (10k) or the (100 ohm) brightness pot. I already have the 68 ohm resistor tied to power the backlight.

Again thanks CD Tech for all your awesome help.
 

CF Tech

Administrator
The 100 ohm pot will dim the backlight. For this backlight a 500 ohm pot would give better range towards dim.

You pretty much need the 10K pot.
 

kparenteau

New member
ok.. I'll add the pots back into the scheme. There have been conflicting web sites on where to start the pots on. I don't want to blow the LCD. I have seen where if you put the pot to "0", or off that .. that is bad. what setting should I put the pots on? Then obviousely I would power on the LCD and start to slowely turn the brightness and contrast up little by little.

Thanks again
 

CF Tech

Administrator
If you put in Rlimit (68 ohms), then you are safe with the pots.

For instance, a 500 ohm pot will (nominally) go from 0 ohms to 500 ohms. The LCD might be damaged if you go below the 68 ohms. When you put Rlimit (68 ohms) in series, then the pot can only be adjusted between 68 ohms and 568 ohms, so it is always safe.

If the 10K pot is connected between +5v and ground, any setting should be safe.
 

kparenteau

New member
Hey CF...

Great support thus far....

The 63 ohm resister is really a 68 ohm one

I put the pots back in...

I useda 1k pot on the backlight and it gives great dim and brightness.

Using the 10k pot on pins 1,2,3 yeils nothing. Meaning it doesn't do anything. I turn it up and down and don't see any difference in output. I then took the pot out and got no readout. I put the pot back in and get read out, but only at an angle

But I'm still at the point where I can barely make out the smartie readout headon, but at an extream angle I can see the readout

I dont know what else to try at this point

Here's where I put the pots



Thanks for everything CF
 
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CF Tech

Administrator
I dono. Should be working. If pin 3 can be set to 1v, and the contrast is not pretty darn readable, then the display probably got damaged sometime in this process.
 
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