ili9341 TJCTM24028-SPI

External hardware connected to the STM32 board
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ag123
Posts: 854
Joined: Thu Jul 21, 2016 4:24 pm

ili9341 TJCTM24028-SPI

Post by ag123 » Thu Apr 27, 2017 3:20 pm

recently while meddling with an ili9341 spi tft lcd TJCTM24028-SPI
e.g. from ebay
http://www.ebay.com/sch/i.html?_from=R4 ... 41&_sop=15

i've initially been doing my various graphics tests powering the tft lcd from the 3.3v pin on maple mini
i came to learn that these boards (i'm not sure if all of them are similar) have a LDO regulator connected to the Vcc pin on the LCD board connector.
https://forum.pjrc.com/threads/28106-Display_ili9341
this means that if u are powering it from a 3.3v pin, the voltage out from that regulator would drop to somewhat low voltages (e.g. in the 2.x ranges), surprisingly i ran the graphics test to completion
on the pjrc forum, one of the solutions mentioned is to short the jumper pin j1, that would bypass the LDO regulator

what i'm doing instead is that instead of connecting to the 3.3v on my maple mini (clone)
i'm connecting the Vin pin on the maple mini to the Vcc pin on the LCD board connector
i'm using the same ground pin as those for 3.3v connecting to the lcd
the result it seemed is a visible improvement in response time, at least on the screen itself. i'm not sure if that's simply a perceived improvement.

but before doing all these, i'd think 1 should perhaps examine the board to see if these hardware (i.e. the LDO) is after all on the board (otherwise pumping 5v into vcc may damage the lcd and maybe even the stm32 board :o )
i used a multi-meter to check voltages at the input to the LDO and output of the LDO, i'm getting a voltage before the LDO around 4.8-4.9v (there is a diode on maple mini i think) and at LDO output it is around 2.98 - 3v, for some reason it did not reach 3.3v possibly due to the Vin being already rather low
the Vin pin is the first pin below pin 0 (pb11) on the maple mini (clone)
http://wiki.stm32duino.com/index.php?title=Maple_Mini
http://wiki.stm32duino.com/index.php?ti ... o_Logo.png
----------
on a side note, i noted that the touch controller is not always there for all similar looking boards on ebay, one should look at the photos and check specs perhaps contact the seller if u are after all looking for one with the touchscreen
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Last edited by ag123 on Thu Apr 27, 2017 4:04 pm, edited 3 times in total.

ag123
Posts: 854
Joined: Thu Jul 21, 2016 4:24 pm

Re: ili3941 TJCTM24028-SPI

Post by ag123 » Thu Apr 27, 2017 3:25 pm

i stumbled into this LDO stuff while searching for a way to use that SD card (note it is not micro SD) slot :lol:
mine has got various series resistors connecting to the SD slot pins

and i found interesting hacks here
https://forum.arduino.cc/index.php?topic=354873.0
and here
https://forum.pjrc.com/threads/28106-Display_ili9341
:D

david.prentice
Posts: 116
Joined: Wed Nov 16, 2016 8:52 am

Re: ili3941 TJCTM24028-SPI

Post by david.prentice » Thu Apr 27, 2017 3:33 pm

My display has the same model number and components. My XPT2046 is a few mm due South of your XPT2046. Otherwise, the pcb traces are similar.

If you connect VCC to 3.3V, short J1.
If you connect VCC to 5V, leave J1 open.

Your STM32 has 3.3V logic. So you do not need any level shifting.
If you do short J1, never connect to 5V.

Make sure that you connect RESET. Make sure that you use the full-fat constructor.
Adafruit examples omit the LCD_RESET argument. This will stop your Display working.

David.

ag123
Posts: 854
Joined: Thu Jul 21, 2016 4:24 pm

Re: ili3941 TJCTM24028-SPI

Post by ag123 » Thu Apr 27, 2017 3:43 pm

yup, earlier i've naively connected my reset on pin 0 (pb11) on maple mini.
it turns out the code check that reset pin is something other than 0 before it does a reset.
*without the reset* right at the beginning of TFT.begin() - that does initiation - 'nothing works' :lol:

imho the standalone LDO on the LCD board is a good thing, shorting that would otherwise mean 1'd likely need to pull 3.3v from the stm32 board to feed the LCD board. using that LDO lets 1 use a 5v input e.g. from the usb connector and reduce the power load on the LDO supplying maple mini/the mcu itself

david.prentice
Posts: 116
Joined: Wed Nov 16, 2016 8:52 am

Re: ili9341 TJCTM24028-SPI

Post by david.prentice » Thu Apr 27, 2017 4:40 pm

Personally, I connect VCC to 3.3V and don't worry about J1. The controller does not take much current. (20mA)
Yes, you lose a few millivolts across the LDO.

I connect LED to 5V via a resistor. This takes about 100mA for 2.2" - 2.4" panels.
If I am using 3.5" - 5" panels, the current might be anything from 150mA to 500mA. Far safer from USB.

David.

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