Hello,
So I've got my first LCD Display and wired it today. But It doesn't work.... Can't see anything on my Display ....
My Display:
The Tutorial I followed:
I hope you can help me once again 
Cheers
Yay it actually works now ! It's fairly visible ! I used a potentiometer for the contrast, but it just goes from fairly visible to not visible. Could it be that I need another potentiometer ?
Cheers
What value Pot is it ?. 10k is the usual value which works for me.
When I turn the potentiometer all the way down I meassure 0 Volts and the text is fairly visible. If I supply it with more than 0 Volts I can't see the text anymore. Can I supply a negative Voltage somehow to the Display ?
How can I check what potentiometer i've got?
And does it actaully make a diffrence, Wouldn't they all provide 0 - 5 V to the wiper?
Cheers
Based on the datasheet on page 8, you need to supply a negative Voltage to contrast pin, here is the simple negative supply generator using CMOS 4049.
Are you sure about that ? Because that would really suck !
I've found something very intresting I guess !
So I've wired the Contrast pin to ground and it's fairly visible again, because it gets 0V again.
Now if I pull out the Power for the Logic wire (The one that is constantly 5 Volts) And put it in again, the displays has a perfect contrast but instead of normal text it then displays some weird characters. If I then press the reset button on the Arduino it goes back to fairly visible. How come ?!
Cheers
Hmmm, remind me to keep buying cheap non-descripts off ebay......
Does anybody know how I could provide negative Voltage to the contrast pin, to trick it out it someway cause I really don't want to build a Negative Voltage generator...
The Negative Voltage could just be constant ! Could I get negative Voltage of a battery ? If yes how ?
Cheers
It actually worked ... Used a 1,5 battery and connected + to GND and - to Contrast Pin.
Anyways why would anyone build a LCD Display with a Contrast Pin which need negative Voltages ?! :-s
So well I guess I bought a very stupid LCD Display ... However I'll buy new one ...
Can anyone confirm that this would be a good display and would not need any negative Voltage ?
Cheers
It looks fine to me but don't take my word for it!
Mowcius
Based on the datasheet on page 8, you need to supply a negative Voltage to contrast pin, here is the simple negative supply generator using CMOS 4049
http://www.freepicsupload.com/pics/phpo6deuO-4049-neg-supp-schematic.gif.
You can use a PWM pin instead of a 4049 to drive the final section (the last two 10uF capacitors and two 1N4148 diodes).
5V Arduino, 50% duty cycle--analogWrite(pin, 128)--and default PWM frequency gives about -3.7V under load to a 16x2 Optrex 16207-CEM LCD.
This particular LCD really needs the negative voltage for contrast.