Arduino 16x2 display contrast potentiometer not working

[MasonMSTY]

i just spent 15min hooking up a 2x16 display but the potentionmeter for the contrast isnt working.
Datasheet for display (  http://www.taydaelectronics.com/datasheets/A-1748.pdf )

this is how i have it hooked up:

Pin 1 to Arduino GND
Pin 2 to Arduino 5V
Pin 3 to middle pin of the 10k potentiometer
Pin 4 to Arduino pin 12
Pin 5 to Arduino GND
Pin 6 to Arduino pin 11
Pin 11 to Arduino pin 5
Pin 12 to Arduino  pin 4
Pin 13 to Arduino pin 3
Pin 14 to Arduino pin 2
Pin 15 to Arduino 5V
Pin 16 to Arduino GND

is this wrong or is something just not working. and is it bad to just not use the pot because it seems to  works fine without it

[wblock]

If the contrast is okay without it, the pot is not required.  It depends on the display.  How are the other pins of the pot connected?

[MasonMSTY]

One Is connected to 5v and the other is connected to ground

[jc101]

The data sheet has the pot as 0-20k, some displays the contrast adjustment is really only at one end of the range or the other. 
Might be worth adding in a 10k resistor in series between +5v and the POT and see if it makes a difference?

[NivagSwerdna]

Here's a link to a very popular shield combo



Personally my displays never work without contrast adjustment via a pot... there is either nothing or every pixel is dark...

[tooki]

i just spent 15min hooking up a 2x16 display but the potentionmeter for the contrast isnt working.
Datasheet for display (  http://www.taydaelectronics.com/datasheets/A-1748.pdf )

this is how i have it hooked up:

Pin 1 to Arduino GND
Pin 2 to Arduino 5V
Pin 3 to middle pin of the 10k potentiometer
Pin 4 to Arduino pin 12
Pin 5 to Arduino GND
Pin 6 to Arduino pin 11
Pin 11 to Arduino pin 5
Pin 12 to Arduino  pin 4
Pin 13 to Arduino pin 3
Pin 14 to Arduino pin 2
Pin 15 to Arduino 5V
Pin 16 to Arduino GND

is this wrong or is something just not working. and is it bad to just not use the pot because it seems to  works fine without it

Can you post a high quality picture of the back of the module? I've gotten some 1602 LCDs where I had to add or remove a resistor to enable the contrast pin.

[mikerj]

The extended temperature range displays often require a negative voltage on the contrast pin.  Even the standard ones require a voltage close to 0v, so you don't tend to get much usable range on a pot wired between Vdd and 0v.

[AustinEngy]

The data sheet has the pot as 0-20k, some displays the contrast adjustment is really only at one end of the range or the other. 
Might be worth adding in a 10k resistor in series between +5v and the POT and see if it makes a difference?

I agree with this.  Whoever designed the product did all of the work for us, and according to them the range of adjustment is 0-20k.  If the adjustment from 0-10k doesn't give desirable contrast, adding the 10k resistor between the pot and 5V will effectively get you an adjustable range of 10-20k.

[Joule Thief]

   measure the DC voltage at pin 3 (VO) on the display. Does it change when the contrast pot is adjusted?

[MasonMSTY]

the dc voltage at pin 3 goes from 0-5v

ill try to add the 10k resistor and see if that helps

[tooki]

The extended temperature range displays often require a negative voltage on the contrast pin.  Even the standard ones require a voltage close to 0v, so you don't tend to get much usable range on a pot wired between Vdd and 0v.

Thanks for this tip! It solved the same problem I'd been having with a large-digit 1602 module. Looks like it needs about -0.93V on the contrast pin! (Annoying, since nothing else in the project needs a negative rail...)

[DJohn]

Looks like it needs about -0.93V on the contrast pin! (Annoying, since nothing else in the project needs a negative rail...)

One ugly hack I've seen is to lift the module above the rest of the system by putting a diode in series with its ground pin.  I don't think I could bring myself to doing this in a commercial product, but for a one-off personal project it is an option.

[macboy]

The extended temperature range displays often require a negative voltage on the contrast pin.  Even the standard ones require a voltage close to 0v, so you don't tend to get much usable range on a pot wired between Vdd and 0v.

Thanks for this tip! It solved the same problem I'd been having with a large-digit 1602 module. Looks like it needs about -0.93V on the contrast pin! (Annoying, since nothing else in the project needs a negative rail...)

ICL7660 to the rescue!
Also, I find that usually, it is a rheostat to ground that is needed, not a true pot (don't connect the other leg to Vcc, leave floating or connect to wiper). Your display that needs negative voltage might even work this way if it has the negative voltage generator built in (most LCDs do).