I just ordered a 2.2 TFT like this one:
https://www.ebay.com/itm/2-2-inch-2-2-SPI-TFT-LCD-Display-module-240x320-ILI9341-51-AVR-STM32-ARM-PIC/401402446990?hash=item5d7573448e:g:RHQAAOSwrOtZtpd4
without Touch, and I will not use the SD.
Can you tell me how much current @3.3V the display needs and how much current for the backlight?
Can't find any information about that.
The Tft will arive in 2-3 weeks so i can't measure it right now - but I would like to move on...
The TFT controller will use about 10mA
The backlight will use about 50mA
The photos in your link show a pcb with yellow header pins, transistor Q1, regulator U1.
You can send the TFT controller to sleep e.g. a few uA
You can turn the backlight off e.g. 0mA
Note that Ebay sellers lie through their teeth.
When the display arrives, compare the pcb with the photos in the link.
Yes, the 2.2 inch screens have an excellent display.
Much clearer and vibrant than the versions with a Touch Panel.
David.
david_prentice:
The TFT controller will use about 10mA
The backlight will use about 50mAThe photos in your link show a pcb with yellow header pins, transistor Q1, regulator U1.
You can send the TFT controller to sleep e.g. a few uA
You can turn the backlight off e.g. 0mA
Thank you!
What does it mean that the headers are yellow?
Is Q1 for switching the backlight?
and what is U1's purpose?
U1 is 3.3V regulator. Default is open J1 and for VCC=5V. Short J1 if you want to use VCC=3.3V.
Q1 is backlight transistor. You can drive it with regular 3.3V GPIO pin or with 3.3V PWM.
Older pcbs often had black header pins. (and no Q1 or U3)
Yellow does not mean anything. But is a hint that you have Q1, empty U3 footprint, empty F_CS pin.
David.
Thanks David.
So, to limit the current consumption my plan was to use a resistor at the LED input, but, as you describe, this is just a signal and not the power line.
My problem is, the current I can squeeze out of my power supply is limited - it is not a energy saving issue, because the display will be switched off most of the time, but for thime it is on, there must be enough current.
In worst case I have about 55mA @ 3.3V, I need 20mA for the µC and another 5mA for some status led.
So there are just 30mA left for this display.
When using PWM to dimm the display with Q1, the current consumption is the same when on.. maybe I can use a fast pwm frequency and some C to average it out, but thats not my favorite.
What do you think about de-solder J1 and short the Base and Emitter Pad to supply backlight from LED pin?
Is there maybe a schematic of this board anywhere??
Any transmissive display requires a backlight. You can get away with a dim backlight if the ambient light is not very bright. In other words, you can use a low average current for the backlight.
If you have bright sunlight or even low ambient light, a transreflective display does not need a backlight.
All digital circuits rely on local capacitors to supply the switching currents. That is why you have 100nF capacitors on every integrated circuit VCC pin.
I would use PWM to control the LED via Q1. You can experiment with PWM frequency. I would expect it will work fine.
Regarding currents. Why are you limited to 55mA ?
Modern LEDs can use < 1mA.
AVR current can be reduced.
ILI9341 current can be reduced.
Backlight current depends on human eyes. Only you can control ambient, aspect, human mood, ...
Battery projects sleep as much as possible. Run at sensible speed for a short time. Minimise average current.
A mains powered project will probably switch off backlight and sleep but is seldom important.
David.
david_prentice:
Any transmissive display requires a backlight. You can get away with a dim backlight if the ambient light is not very bright. In other words, you can use a low average current for the backlight.
If you have bright sunlight or even low ambient light, a transreflective display does not need a backlight.Regarding currents. Why are you limited to 55mA ?
Modern LEDs can use < 1mA.
AVR current can be reduced.
I use a bus system with power supply (KNX) and the bus transceiver I use is limited to that amount of current.
Yes, maybe I can reduce the current the other stuff needs, but maybe not.
In most cases the device will be used in switch cabinets in basements or other dark places, so I dont need it to be very bright.
But how much reduction is possible I have to figure out myself...
The first experiment is to see what PWM value gives a readable display. i.e. what average backlight current.
If you don't need fancy colours, how about a monochrome COG display?
David.