Hi community !
I'm programming on an Arduino Mega with this display and I see that is no possible to turn off backlight by program on this display. I'm looking for technical information on how to rewire it to be able to turn the leds on and off. Can someone indicates me some link to do that ?
Thanks in advance !
Hi community !
Please post a link to the actual display that you bought e.g. Ebay sale page.
Thanks for your reply !
Information about the device :
VMA412 is a 2.8 tft LCD from Velleman with driver ILI9341
Here's a link to the product overview (with diagram) : Product overview
Here's a link to the display user manual : User manual
Here's a link to the display datasheet : Datasheet
Image of the board.
I think it could be possible to interrupt the circuit somewhere on the board (around the top right mofset ?) before the leds and wire it to a free pin of the Mega (toward a mofset or even a relay), but I don't know exactly how to do it. I need to create a management console for some automotive purpose where power management is important.
 I seen your Post that is very instructive, but I would need some details about how to actually do it. I'm a C programmer not too good at electronics. I thought to unterrupt the line between the VCC pin and the mofset and rewire it to the VCC line toward a relay controlled by a digital pin from Arduino, but I not sure to be right ...[/edit]
Please read the part numbers of U2, U3.
Read the value of R1.
I am not at a PC. If your manual has a schematic it should be possible to add an external transistor but a bit fiddly.
U2, U3 part number : LVC245A KD05301 TXD547F (See attached file)
value of R1 : Is written "103", I think is : 0.125W. 10K
Thanks for you help.
 If you think is very complicated to do so, I was also thinking about to directly handle the VCC pin of the display and to add a switch to the arduino to inform the board/program to power on (and initialize) the display when needed, but I'm not sure if it will work.[/edit]
Bad news. Your original photo shows a Blue pcb. Your last photo shows White pcb.
Please confirm whether the Blue photo has the same copper tracks, components, ...
Good News !! You have the correct 74LVC245 chips.
Measure R1 with a DMM. I was expecting 5R1, 10R, 15R, ... and not 10k
Your docs do not show a schematic. If R1 is 10k you have no hope of switching the backlight.
If it is 10R please measure connectivity between left terminal and each pin on the AMS1117.
Repeat for the right terminal.
Thanks for your help David.
I thougth it was the same because of the general layout and same driver, but it seem's is not exactly the same. The wiring seems a little bit different and the resistor too. Sadly I can confirm is a 10k resistor. I dont understand why Velleman don't gave the possibility to do some power management on this board.
Think about it. A Uno shield has got limited pins. A TFT with 8080-8 parallel interface uses 8 data + 5 control signals. The SD uses 4 SPI signals. Serial uses 2 pins.
A5 is the only "spare" pin. Which you can use as Analog / SPI_CS / OneWire.
If you have a SPI TFT there are several spare pins for external hardware. And Adafruit / WaveShare / Seeed SPI Shields give you backlight control.
You still need level shifters with SPI but SPI shields provide the necessary electronics.
SPI is slower than 8080-8 on a Uno. SPI is faster than this 8080-8 shield on a Mega2560 (due to the random pin mapping)
If you want a fast TFT on a Mega2560, buy a Mega Shield in the first place.
Seriously. Why turn off the backlight. A motor car has plenty of battery power. And you would always wire any instrument via the ignition anyway. i.e. instruments only work when the car is running.
Thanks for all the words you spent here ! For sure I would not have bought this display ...
Yes I can buy a more cool device and will do that in the future ...
I'm turning a little truck in a fully functional moving house running on solar panels and batteries ...
My problem here was to save battery life and that I don't want to have this display always on because it seems to me a little bit strange to have it always on.
Also I thought it was a good thing for other people who wanted to do so to get some information about that.
I will try my other way to cut all the display on/off and try to reinitialize it when needed. I will also post here my results.
Thanks a lot for your help ! Have a good day !
I did it !
I finally unplugger the VCC pin of the display and rewired it on a VCC controller by a simple relay.
I think the important thing is to correctly initialize and deinitialize the display before power off and after power on.
Is working like a charm.
Thanks a lot !