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Touch LCD chat

A: LCD TFT screen 2.8″ ILI9341 SPI connect

tlfong01Question SPI 2.8″ TFT LCD ILI9341 Rpi3B OK? Answer Well, 60% chance OK. First thing first – check out spec and schematic. The OP’s question is clear, and his reference web links are very good. So I followed his links and jot down a picture of the wiring. The drive/library r…

Ephemeral
Ephemeral
Thank you very much, I have already seen (hover over) all the tutorials provided but I do not understand how to connect “BL” (from ILI9341 Raspberry Pi guide – pi0cket) for example, I can not see it on the diagram (that you kindly highlighted me). Another remark is for pin SPI_SDO, SPI_SDA there is NC / SPI_, the NC scares me …
tlfong01
tlfong01
Ah, no problem. Perhaps I can draw a diagram to explain it better.
Ephemeral
Ephemeral
It would be with great pleasure but I would not want to take up too much of your time.
tlfong01
tlfong01
Ah I see your problem. They are using hard to understand geek language. “NC” usually means “No Connection”. “BL” usually means “Back Lit”. The module has 4 white LED which can back light the background. No problem for me drawing anything. It take me very littl time.
Ephemeral
Ephemeral
Thank you very much again for all your explanations. I think at this time, GPIO9 -> LCD_RD , GPIO10 -> LCD_WR, GPIO8 -> LCD_CS  but for RESET and RS (Register Select ?) no definition on pinout shematic for the raspberry. Maybe these pins can be any pin gpio (declared in the driver source file?) raspberry pinout
tlfong01

tlfong01
yst 21:17
Yes, it is confusing. I am trying to make some educational guesses, as in the coming updated picture. BTW, my answer is not just for you, but a follow up of other touch screens answers for newbies. For me it is just like a jigsaw puzzle, which is my hobby of playing electronics toys. Now I am going to meet a friend for supper. So see you tomorrow. Have a nice project!
Ephemeral
Ephemeral
I can not thank you enough. Have a good dinner. I will work with the elements of your updated answer.
tlfong01

tlfong01
@Ephemeral I googled more touch LCD user guides and found all of them similar. So I have drafted a basic wiring diagram as updated. I think you can find the SPI signal lines at the Arduino shield plug CON 1, and one more CS signal line for micro SD card at the bottom side of the PCB. (Main SPI line are shared between LCD and sd card。) I could not find any BL line in your board. Perhaps your board has no back lit. Or you can try searching for it. I am going to gym then supper. See you late evening or tomorrow. Good luck!
Ephemeral

Ephemeral
Again, thank you very much. For ‘BL’, I can see LEDA on pin 16 and LEDK on pin 17 (LEDA seems to be the only pin needed on the diagram), but I really do not understand the pin mapping for the final board. And then what would LEDK be used for ? … Have a good supper.
For SPI it means that I can not make a display request and a request to access the SD card at the same time ? Can we say that this works in half-duplex ?
tlfong01

tlfong01
1419
Ah. LEDA means LED Anode, which means Positive. LEDK means LED Cathode, Negative side. So if you connect Anode (to be very safe, use 1k in series to limit current) to 3V3, and Cathode to Gnd, the back lit LED should light up.
Ah, let us consider one device at a time. A SPI operation is almost always write and read at the same time, sort of mouth talking and ears listening at the same time. So it is full duplex, if you wish to use this term half/full duplex. Same for SD card, you write and read at the same time. Now you can read a byte from LCD and then write the byte to SD. But this has nothing to do with half or full duplex, I think, not very sure, again. You need to wiki for SPI, and also google Rpi newbit tutorials on SPI and I2C etc, to clarify.
Ephemeral

Ephemeral
Thank you for all your clarifications. For the lighting the schema of the diodes watches a schema with a pin named ‘A’ and 4 Leds in parallel. It seemed to me that LEDA could have been used for this pin. Yes, you’re right, I’m going to read the ILI9341 data sheet provided by adafruit to read a bit more about SPI and I2C. But I do not know if it will allow me to find the connection for the spi clock, the back light etc … because everything is on the diagram of the screen finally.
tlfong01
tlfong01
yst 21:17
Ah, the four most important spi wires you want is located in CON1. Look for this plug in my picture updated yesterday.
Ephemeral

Ephemeral
Yes I will look even more carefully. After thinking, in fact, I should not rather look at your last schema which is much clearer for me and my level because I can not find a match for the clock for example apart from in your last scheme. If I understand what you told me before then I just miss the pin for the back light. But I am beginning to doubt my ability to properly configure the outputs in the driver source since I can not easily understand a simple connection and associate the technical terms.
tlfong01

tlfong01
1419
Yes, I agree. If you cannot guess the meaning of terms BL = Back Lit, and LEDA, LEDK mean Anode and Cathode, then it is very difficult to do it all by yourself. But then if you read AdaFruit’s newbie tutorials on touch LCD, you might find things not that difficult. Or if you search Amazon’s touch LCD for Rpi, you might also find it easy. Your problem is now you want to change an Arduino shield to Rpi compatible, that is indeed very difficult. Suggestion: watch what I do this weekend, then decide to give up for now and come back later, after learning SPI basics.
Ephemeral

Ephemeral
330
Thank you. I understand you, but I am simply confused because I have a little experience of programming with SPI. On the original vellman diagram, you have highlighted 5 ‘wires’, on the diagram of lallafa’s 4 ‘wires’ are highlighted. When I program an ATtiny (which happened to me once or twice) with SPI I use 4 ‘wires’. I do not try to make all the features of the screen, touchscreen, access to the SD card etc but rather to do a simple SPI link is to write text to start,I have this screen on hand so I thought maybe it’s possible to just connect to the raspberry.
tlfong01
tlfong01
Ah, you only need 4 wires for the LCD – CLK, MOSI, MISO, CS. The 5th wire is CS for the SD card. So actually we don’t need to bother the SD card, or even the back lit, just play with LCD to start with. As I said, you can just sit back, do nothing and watch how do I test the very basic SPI thing over the weekend, …
Ephemeral
Ephemeral
Thank you very much for everything.
tlfong01

tlfong01
yst 21:23
@Ephemeral You might like to read my answers to two 7″/5″ LCD questions at the end of the references. Very sadly, I could not give them a good answer. I heard that WaveShare 7″ and 5″ touch screens are problematic. So this 2.8″ LCD is my third attempt. Actually I know very well how to do 4bit/8bit and I2C LCD. This is the first time I am doing SPI LCD. So at the very beginning I said there is only 60% chance of success! 🙂
3 hours later…
Ephemeral
Ephemeral
0:08
Yes, no problem I understand.
The last message was posted 9 hours ago.

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