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backlight of 2x16 lcd

http://forum.cytron.io/viewtopic.php?f=8&t=10901

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backlight of 2x16 lcd

PostPosted: Tue Mar 15, 2011 9:00 pm
by kwlew
Can i just directly connect the LED+ to 5V and LED- to ground, or need to connect the LED+ to the microcontroller pin?

Re: backlight of 2x16 lcd

PostPosted: Wed Mar 16, 2011 11:13 am
by FloatingMachine
You can connect the LED+ directly to 5V if you do not need to control the back light.

Otherwise, you can use a transistor to turn on/off the back light with your MCU.

Re: backlight of 2x16 lcd

PostPosted: Wed Mar 16, 2011 11:28 am
by Brian Griffin
kwlew WROTE:Can i just directly connect the LED+ to 5V and LED- to ground, or need to connect the LED+ to the microcontroller pin?


You can do both, but for the microcontroller, connect it to a transistor first.

Btw, put a current limiting resistor inside with the LED too.

Re: backlight of 2x16 lcd

PostPosted: Wed Mar 16, 2011 3:03 pm
by kwlew
if i just directly connect the LED+ to 5V, then do i need put any resistor between it? if so, what value will suitable?
Thanks.

Re: backlight of 2x16 lcd

PostPosted: Thu Mar 17, 2011 2:15 pm
by ABSF
My GLCD backlight is using 4x SMD 100 ohms resistors in parallel making it 25 ohms. You may try resistors between 25 to 100 ohms. Just see which one is best for your eyes.

Allen

Re: backlight of 2x16 lcd

PostPosted: Fri Mar 18, 2011 11:08 am
by FloatingMachine
I always connect the LED+ to 5V directly without any problem. There are already a current limiting resistor on the LCD. Just that the 7805 might can a bit hot.

Re: backlight of 2x16 lcd

PostPosted: Sun Mar 20, 2011 11:31 am
by robosang
I think Cytron did share about this in one of their article, the robot magazine, but cannot remember which version.

According to the author, the backlight can be directly connected with 5V, but the current consumption is quite high and will further increase the load of the 5V regulator, end up? Your 7805 is hot :D . The author share the method of controlling the backlight using PWM via a NPN transistor. With this configuration, you can control the brightness from the microcontroller and further control the current consumption.

And normally you don need such high density light to look at the character on LCD. You can try the value on SK40C's schematic, I just apply what is being use by Cytron and it work fine for me, if I am not mistaken is around 50 Ohm.