NHD-0216BZ-FL-YBW: values for a trimpot for LED backlight?

[GK]

Hello!

I installed the NHD-0216BZ-FL-YBW display into a synthesizer, and now I have an overheating problem (the LED backlight is also too bright). The input voltage that goes into the backlight power contact is 5V.

As I understand, I have to install a trimpot resistor to Pin 15 to decrease a voltage for LED backlight.

Could you please let me know the necessary values for a potentiometer, so I could smoothly tune up the LED backlight intensity from dimmed to maximum?

Thank you,
Gregory

[Paul_B]

Hello Gregory,

I recommend using a 10K potentiometer 

This will let you adjust the contrast. Each LCD will have slightly different contrast settings so adjust accordingly and always consult with the displays datasheet.

http://www.newhavendisplay.com/specs/NHD-0216BZ-FL-YBW.pdf

Hope this helps!

[GK]

Dear Paul,

Thank you very much for your reply.

My question was about the brightness of LED backlight, not about the contrast setting. Are the contrast settings affect the LED backlight brightness? Am I missing something?

Gregory

[Paul_B]

In a Liquid Crystal Display (LCD), V0 is used to vary the screen brightness or contrast. Contrast, simply put is the ratio of the light areas to the dark areas in a LCD.

[GK]

Thank you for your detailed reply.

According to specifications, the LED backlight requires 5V @ 120mA, which is (according to ohm's law) 42 ohm.

Why can't I just use a 42 ohm resistor (a trimpot) on the "LED+" contact to vary just the LED backlight brightness? The display's contrast is good.

Again, thank you for your support, I appreciate it very much!

[GK]

Dear Paul,

I have just discovered that according to the documentation, there is on-board resistor for LED backlight.

Currently, the two wires for LED Power Supply are soldered not to "LED+" and "LED-" pins 15 & 16, but into "A" and "K" contacts on the side of the display.

Do they have to be soldered to pins 15 & 16 in order to use the on-board resistor? Could you please let me know the on-board resistor value?

Thank you,
Gregory

[Saurabh_B]

Hi Gregory,

It looks like were having trouble sending an email to you last night, but you want to have the backlight anode connected to pin 15. The on resistor is in series there, if you apply the power to the A directly you could damage the backlight.

[GK]

Thank you very much for the info.

Could you please let me know the value of the on-board resistor?

[Saurabh_B]

It is a 6.8 Ohm Resistor.

[GK]

Thank you very much! I only have one question left:

According to documentation, the LED backlight requires 5V @ 120mA, which is (according to ohm's law) 42 Ohm.

If this is correct, then the on-board 6.8 Ohm resistor will provide a current of 735mA instead of 120mA (still too much). With this in mind, do I have to put an extra resistor (or a trimpot) to the pin 15 to get a current of 120mA?

[Saurabh_B]

You wouldn't have to, the 6.8 ohm resistor is dropping the voltage down by 0.72 V so voltage drop across the backlight is 4.28V.


I just hooked up a the sample which I used to confirm the resistance to a power supply. While at 5V it is using 125 mA. so in this case the resistor is dropping the voltage by .75V, from which the backlight has a drop of 4.25V. You can attach a potentiometer to pin15 to drop the voltage further and decrease the brightness if you would like.