Go Down

Topic: Displaytech 162 (16x2 LCD) broken? (Read 2908 times) previous topic - next topic

therealone

Oct 18, 2012, 12:13 pm Last Edit: Oct 18, 2012, 12:15 pm by therealone Reason: 1
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

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!

liudr

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.

therealone

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?

liudr


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.

floresta

#4
Oct 19, 2012, 12:07 am Last Edit: Oct 19, 2012, 12:09 am by floresta Reason: 1
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

therealone

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

dhenry

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.

floresta

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

floresta


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

dhenry

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.

liudr


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.

Go Up