Controlling LCD B/L

[Charles Linquis]

The backlight of an LCD generally cannot be controlled through the digital interface.

You will need a FET (I use an FDC610) with the source connected to GND, the drain connected to the backlight (-) terminal, and the backlight (+) terminal connected to 5V. Your LCD may require a 5 ohm .5W resistor between the (+) terminal and 5V to limit the backlight current (check the datasheet).

Connect a 10K resistor between the FET gate and GND and also connect
the gate to a PIC output pin. Whenever you want to turn on the backlight, bring the output pin high.

[Melanie]

http://www.picbasic.co.uk/forum/showthread.php?t=794

[solidus]

Hi Melanie,
Do I have to use pwm for lcd lihgt ?

[Acetronics2]

Hi,

As I do not understand your comments and variables ( Turkish ??? )

One good question would be :

What do you want to do ???

- on/off control ??
- dimmer ??

Alain

[Melanie]

Well, you don't have to use PWM... but if you do, then you will have control over the Brightness and will be able to adjust for your own comfort level. If you have two PWM channels available, then you can do the same thing for your LCD's Contrast. Search the forum for Easy Contrast if you want to do that.

If you just want to turn your LCD's Backlight ON/OFF then any I/O Channel will do, but you must know how much current the Backlight will require... if it requires more than 25mA, then you need an external Driver of some sort.

[Charles Linquis]

If you just hook things up like I describe above (using an N-channel, logic-level FET driver) all you have to do is set the pin to "1" to turn the backlight ON, and set it to "0" to turn it off.

PWM is not required unless - as Melanie says, you want to control the brightness of the backlight. And I have never seen a backlight that takes less than 200 mA.
You will not be able to drive the backlight directly from a PIC pin.

[Melanie]

Actually Charles, the 'Cool Blue' displays take about 20-25mA to give you more than adequate illumination (as they only have a single high-intensity white LED performing the Backlight - rather than a whole bank of Yellow or Green LEDs). You can drive those directly from a PIC pin... and they've been around for about five/six years now...

See post #12 here...

http://www.picbasic.co.uk/forum/show...ight=cool+blue