Arduino Forum

Using Arduino => Displays => Topic started by: therealone on Oct 18, 2012, 12:13 pm

Title: Displaytech 162 (16x2 LCD) broken?
Post by: therealone on Oct 18, 2012, 12:13 pm
I cannot get my Display working. I have connected it as follows:

the only difference is that i used a 2.5kOhm instead of the 10K Poti.

This is my actual setup:
http://bayimg.com/daepPaaed (http://bayimg.com/daepPaaed)

I have the feeling that the LCD is broken because i cannot get anything when running the LCD-Example from the Arduino Database. But since i havent worked with LCDs before maybe I have made a mistake and somebody can tell me.

Thanks in advance!
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: liuzengqiang on Oct 18, 2012, 06:28 pm
No you did NOT have a 2.5kohm or a potentiometer. What you have is a resistor or unknown value (your photo color is pretty screwy so no way to tell resistance from color). You also didn't solder the pins to the LCD.
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: therealone on Oct 18, 2012, 06:40 pm
Thanks for the answer! Two questions though:

1.) Do I have to solder the pins the the LCD? Doesnt it get contact otherwise?
2.) I tried a 2.5kOhm resistor and a 10kOhm resistor so far. A Resistor does the same thing as a potentiometer, only it has a fixed value, right?
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: liuzengqiang on Oct 18, 2012, 10:07 pm

Thanks for the answer! Two questions though:

1.) Do I have to solder the pins the the LCD? Doesnt it get contact otherwise?
2.) I tried a 2.5kOhm resistor and a 10kOhm resistor so far. A Resistor does the same thing as a potentiometer, only it has a fixed value, right?


Yes, you solder the pins on. No alternatives.
A potentiometer is a variable resistor. You can't vary those cylindrical resistors that you are currently using. If you are in a hurry, go to a local radio shack store and get a potentiometer anywhere between 2k and 20k. Otherwise, get a pack from ebay.

Also, put your location information in your profile. Some people can give you location-specific information. Like I can tell you where to get parts locally cheap if you are in my area.
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: floresta on Oct 19, 2012, 12:07 am
Quote
A Resistor does the same thing as a potentiometer, only it has a fixed value, right?

Wrong.  Your statement would be correct if you replaced 'potentiometer' with 'rheostat'.

Quote
A potentiometer is a variable resistor.

That's not exactly right either.  Your statement would also be correct if you replaced 'potentiometer' with 'rheostat'.

At the risk of over simplification:
A resistor has two terminals and has a fixed resistance between those two terminals.
A rheostat has two terminals and you can adjust the resistance between those two terminals.  So, a rheostat is a variable resistor.
A potentiometer has three terminals.  It has a fixed resistance between the end terminals and a variable resistance between the center terminal and either end terminal.  A potentiometer is essentially a variable voltage divider.

So, for LCD contrast control, there really is no way to replace the recommended three terminal potentiometer with a single two terminal resistor.  There are those who claim to have conjured up 'solutions' using a single resistor or a single diode that have supposedly worked in certain cases, but I suspect a wad of bubble gum would have also worked in those cases.

You could try connecting pin 3 to GND.  That gives a usable, but not optimum, display in some cases.

If that doesn't work you might be successful using two resistors.  Try something around 10K between +5 and pin 3 and around 1K between pin 3 and GND.

Don
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: therealone on Oct 19, 2012, 11:51 am
Thank you so much! It is working now. I connected Pin3 to GND like advised and soldered the display.

Here is the result: http://bayimg.com/gAeJNaAee (http://bayimg.com/gAeJNaAee)
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: dhenry on Oct 19, 2012, 01:19 pm
Quote
there really is no way to replace the recommended three terminal potentiometer with a single two terminal resistor.


A pot is the simplest way to go. But it is extreme to say that there is other alternative. For example, you can pwm through a rc network to create a voltage there, and be able to adjust contrast in software.
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: floresta on Oct 19, 2012, 03:31 pm
Quote
Here is the result:

That's not too bad in terms of my "usable, but not optimum" remark.  You could get rid of the light blocks in the unused positions if you added a potentiometer but it probably isn't worth the effort.

Don
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: floresta on Oct 19, 2012, 03:40 pm

Quote
there really is no way to replace the recommended three terminal potentiometer with a single two terminal resistor.


A pot is the simplest way to go. But it is extreme to say that there is other alternative. For example, you can pwm through a rc network to create a voltage there, and be able to adjust contrast in software.


In your haste to correct me it appears that you left out a word that reverses the meaning.  Either way - read the quoted part again, I didn't say that there is or is not another alternative.

Don
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: dhenry on Oct 19, 2012, 03:50 pm
In your haste to accuse me of in a haste to correct you, let me make it clear to all: correcting anyone, you included, is the least of my haste.
Title: Re: Displaytech 162 (16x2 LCD) broken?
Post by: liuzengqiang on Oct 19, 2012, 06:41 pm

Quote
there really is no way to replace the recommended three terminal potentiometer with a single two terminal resistor.


A pot is the simplest way to go. But it is extreme to say that there is other alternative. For example, you can pwm through a rc network to create a voltage there, and be able to adjust contrast in software.


You are offering help to a beginner or trying to show you know more than others? I'm confused here. As a teacher, I don't always tell my students the "complete" story on day one. There are reasons not to tell "complete" stories. I will wait at least another 30 days for the OP to get the RC stuff, which I'm sure floresta knows how to do. Right now, potentiometer is perfect. I am a teacher and liquid crystal physicist, do you see me blabbing about knowing all more about LCD stuff than others? Most HD44780 display spec sheets I read didn't say they recommend RC and PWM anyway, they say 2k to 20k pot.