Hi, is there any trick to the displayHX8357 brightness control software? I use the TFT_HX8357.h library and I haven't read anywhere if it can. Thank you for your feedback and have a nice day
Please post a link to the actual display that you bought.
Then you will get an accurate answer.
Ok, Thank you very much ... HX8357C on Raspberry Pi · Issue #4 · bitbank2/SPI_LCD · GitHub
I would be happier if it was a link to an actual sale.
However the photo dated Nov 5, 2017 is a common display. It might have HX8357-C, HX8357-D or ILI9481. There is no Touch Panel.
It should work 100% with Bodmer's TFT_HX8357.h library.
The controller model would have been printed on the anti-static envelope label when you bought it.
It is not possible to dim the backlight.
David.
Thank you where I bought the display, I don't remember it being "out of the drawer". The type is HX8357C. Yes, it works with the TFT_HX8357.h library. and has no touch layer. It was just a matter of regulating the backlight to save energy. Another view - would the display go out completely if the + 5V pins were powered from the Arduino output? I wonder what I could do wrong before I do. Anyway, thank you for the answer and have a nice day ...
You connect the 5V pin to the 5V socket. It is a Shield which plugs into the Mega2560 18x2 header as Nature intended. The wiring is fixed. It picks up RESET and 3.3V from the 2x1 header
There is no point in reducing the supply to the Mega2560 because U1 regulates this voltage to 3.3V on the Shield.
Does your screen get warm? Or hot ?
David.
Thank you, the display doesn't heat up, I'm just wondering how to turn it off because I want to save battery power. So I wondered if it would be possible to power the display from the Arduino output and after a while turn it off completely.
Provide some real numbers. e.g. battery capacity, expected battery life, active profile, ...
Operating an LED backlight from a battery is expensive.
A 3.5 inch TFT's backlight might draw 100mA.
You would need a very large battery if you want more than 10 hours operation.
Ok for battery backup of a mains powered item but not practical for a fully battery powered item.
You would need to modify the hardware on the TFT shield to access the backlight separately.
Or it might be simpler to switch the whole unit off completely i.e. Arduino and TFT
A MEGA2560 is not suitable for a low-power battery app. Nor is a backlit TFT.
Choose more suitable hardware. Sleep the TFT controller, Sleep the MCU, switch off the TFT backlight.
David.
In the end, it worked. For those who might be interested: The SMD resistor is marked R1 on the board. It is connected to ground, the second terminal then leads (I think) to the LED cathodes to illuminate the display. In series with resistance i inserted a transistor that I control with a PWM signal from Arduino. How simple 
Thanks and nice Day!
The hardware mod for that Shield is pretty simple.
You could glue the transistor and 2R2 resistor to the shield pcb. Then use one of the unused digital pins 44, 45, 46 for the PWM.
You never said what hours or battery life you want.
For minimal current, you send a SLEEP command to the HX8357C as well as turning off AVR peripherals when the AVR sleeps.
David.
I don't know exactly which battery to use yet, I'm thinking of a power bank for easy charging. So 3000mAh. I tried to put the display to sleep writecommand (0x11) and I have a few more milliamperes for good I can't put the Arduino to sleep, it will work with three small (1.8 '') TFT displays with data on it. The big one is only for setting, then I put it to sleep. Do you have any experience with OLED displays? With them, the power consumption could be further reduced. But I can't detect any RGB display. Anyway, thank you for the advice. Have a nice day.