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### Topic: Problem with connecting an LCD 16x2 (Read 8234 times)previous topic - next topic

#### Yaro

#30
##### Mar 12, 2012, 12:24 am
Ok, so i'll try with a 150ohm on led+ and i'll say if it work.

#### floresta

#31
##### Mar 12, 2012, 03:26 am
Quote
Yes correct the diode won't limit the current directly however it will do the thing, since 4.2v and 0.7v add up to 4.9 volts. I use it myself, the LED backlight has a resistor but that is not enough, very bright, adding a diode, brightness dropped down to moderate levels. It's not always handy to have so many resistors around.

The problem is that you just don't understand the theory.  The voltage drop across a diode is a dependent variable.  It depends on a specific amount of current flowing through the diode which must be determined by some external component, typically a resistor.

The LEDs in the backlight will only exhibit a voltage drop of 4.2 Volts when their nominal current flows through them.  The series diode will only exhibit a voltage drop of 0.7 Volts (assuming it is a typical silicon power diode) when its nominal current flows through it.  The diodes themselves cannot be used to control or determine this current.

Don

#### takao21106

#32
##### Mar 12, 2012, 03:45 amLast Edit: Mar 12, 2012, 05:15 am by takao21106 Reason: 1
Do you believe I am unaware of this? It works since the coefficient is positive. This information can be found inside datasheets.

Here's also a circuit where I use a LED to get the right voltage level for digital inputs.
http://arduino.cc/forum/index.php/topic,96189.0.html

I have read the complete thread again, looked at the photos and I saw the videos.
Seems to be it is a white backlight and they don't draw as much power as the green one's.
If the brightness is moderate then it is OK no extra parts are required.

Here is someone using this LCD without microcontroller:
http://iamsuhasm.wordpress.com/tutsproj/using-lcds/ (in 8bit mode)

They are also having problems (with the connections):
http://walkingwithtux.wordpress.com/2010/05/01/jhd162a-lcd-display-3-wire-interface-with-arduino/

#### Yaro

#33
##### Mar 12, 2012, 10:16 pm
I have solved, the problem was the connection from pins to arduino, the guide configuration didn't work for unknown reason, i have tryed to use connection specified in the "helloworld" sketch and worked.

#### TWCP0104

#34
##### Mar 15, 2012, 01:58 pm
So, what configuration did you use? Would it be too much to ask for you to take some pictures? I'm having the same problem and it's driving me crazy.

#### floresta

#35
##### Mar 15, 2012, 10:26 pm
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So, what configuration did you use? Would it be too much to ask for you to take some pictures? I'm having the same problem and it's driving me crazy.

Why don't you start a new thread.  Outline your problem, show us your sketch, give us a picture, and we can probably get you going pretty quickly.

Don

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