Controlling LCD screen backlight with arduino

Hi,
I have a Pixel Qi display (pq3QI-01), it's a display that has reflective mode (can reflect ambient light so it's well visible in the sun). It's a laptop panel that needs a controller board(i have a m.nt68676.2) to make it work. The controller board doesnt control the backlight. I'd like to use the backlight at 10% intensity, i was hoping to use arduino PWM to achieve this, according to the documentation:

Page 13 contains information about the backlight.
Luckily the set of cables that connects the display to the board are divided in two, one group managing the display's LVDS interface and another group the backlight unit.
The controller board (m.nt68676.2) already provides voltage(12v), ground and EN Control Level(5.5v, to enable or disable the backlight)
I was planning on attaching the PWM Control Level cable to a PWM pin on a Leonardo and have the Leonardo send the signal to control the brightness through duty cycle.

Would this work?
Would i need to add a resistor between the Leonardo and the display or the board?
thanks

Looking at that datasheet the Leonardo’s pwm signal is within spec for both voltage and frequency.
However there is a formula(page 14) to determine optimal PWM frequency based on frame rate(I think) but, the math is beyond my ability. I would try it and see. Don’t use a resistor. If it doesn’t work the pwm frequency can be adjusted.

10% Intensity is pushing the boundaries for that display. It’s possible you could experience flicker at that setting. You may need to bump that up to 15-20%

Here is how to use a led as a light detector to tell how bright the screen should be.

https://playground.arduino.cc/Learning/LEDSensor/

Here is the Mitsubishi white paper on their apps using leds, one is to detect how bright the background is automatic control remote control brightness. Otherwise the user has to have some way to do it.

Hutkikz:
10% Intensity is pushing the boundaries for that display. It's possible you could experience flicker at that setting. You may need to bump that up to 15-20%

PWM cycles are 2ms and 1ms. Human eye is fooled into seeing motion at 24 FPS with some hint of flicker. That is over 40ms per frame. Old NTSC TV showed 30 FPS and displays at 40+ FPS == 25ms/frame just look more real.

You can't see PWM flicker but you can see soft-PWM flicker at about 50ms/frame... done it just to make leds flicker "like stars" before only longer than 50ms for more effect.

When using the led as a light detector sketch I did notice that in low light it took so long making a read that the led flickered (the sketch used the led as both source and detector to control its own level) which I took as the sketch needing a timeout on reads, as lowest level below which brightness is not adjusted.

from the datasheet:

Note (2) If the PWM control duty ratio is less than 10%, there is some possibility that acoustic noise or backlight flash can be found. And it is also difficult to control the brightness linearity

Some possibility. Wow. Don't even try then, it won't work.

The manufacturer thought it important enough to include in their datasheet. So I passed it along.

nothing more.

Hi,
Thanks for replies.
Sorry i don't know much of electronics, just the basics. Can i plug in the arduino to the computer for power and just connect the PWM signal pin to the PWM cable of the panel? Or i have to connect VCC and ground to the rest of the circuit?

You could make a voltage divider with a resistor and pot to supply that pin. Adjust brightness with the pot then.

GoForSmoke:
You could make a voltage divider with a resistor and pot to supply that pin. Adjust brightness with the pot then.

Hi, you mean that by using a potentiometer i can achieve the same as if i was using arduino with PWM?

You get a knob to turn and the backlight gets analog voltage, not PWM to control brightness.
It is manual-only control.