kedei 3.5 inch spi tft lcd arduino pricelist

When surfing for information on 3.5 ” TFT touchscreens for the Raspberry Pi,to improve the TinyLCD experience, I stumbled upon AliExpress where several shops offer a 3.5″ LCD TFT Touch Screen Display for incredible low prices.

Update June 2016: There is now a download/information page at http://osoyoo.com/driver/rpiscreen.php. Images for more versions (mine i 2.0, latest is 6.2)  are available there. Alternative ishttp://kedei.net/raspberry/raspberry.html with Kali Ubuntu drivers too for version 3.0 and up.

The archive contains an image of Raspbian with the LCD driver installed. The image is quite current, and fit for B, B+ or 2 B. When I bought the screen an older image, build in augustus 2015,  was downloadable, the kernel is quite fresh built, early October 2015.

The image supplied is wheezy,  3.18.9-v7 #27 SMP PREEMPT Sun Oct 4 23:57:41 CST 2015 armv7l. So quite a recent system! Also the Model 1 B and B+ kernel is present, also just current wheezy.

The system uses SPI to copy the screen contents to the LCD screen, and some GPIO’s for the touchscreen. Other GPIOs are free, and the connector construction  leaves these pins indeed accessible!

Is there a chance of getting it working with an Arduino Uno R3 or Mega2560? The graphics libraries that use SPI that I"ve found keep mentioning the RST and DC lines, which aren"t present on this board.

I haven"t had the opportunity to try it on a Raspberry Pi yet. From pinouts of raspi (googled images) they only have one long strip of GPIO/etc connectors, do they not? Even if plugging this board onto the 40-pin connector, where the two 5V pins match up, on the raspi the opposing two aren"t GND, they"re listed as "+3,3V" and "SDA". Something tells me that.. well, either I"m missing something, or this display needs some form of connector between itself and the raspi it"s meant to run off originally. (Oddly enough, they came with raspi-with-TFT-on-top plastic enclosures, which wouldn"t leave any space for rewiring pins.)

I doubt it. It would be a lot cleaner with regular SPI for both. You just change mode each time. e.g. 9-bit mode #3 for TFT. 8-bit mode #0 for the XPT.

Ah-ha. The HC595 is a shift register. They might use them to produce 16-bit parallel to drive the TFT. If they do, it will be a nightmare. Even worse than 9-bit SPI.

Well, it"ll be interesting to see if I get this to work eventually. A quick guess would be that with L_CS pulled low, the LCD chip gets to talk with the MISO/MOSI lines. After initializing it, I suppose the next step will be to (read datasheet..) and see if the MISO/MOSI-lines are used to clock out display data with L_CS high so the LCD chip doesn"t listen to that garbage, or if it is meant to be fed through the LCD chip aswell.

16-bit modules are cheaper than SPI display modules. So it is quite possible that he has crippled the display with shift registers instead of buying a proper SPI module.

Oh, this makes it easier - googling for the tarball I needed (lcd_show_v6 for my board since it"s got "v6.1" printed on it) got me to OsoYooTFT/README.md at master · jgamblin/OsoYooTFT · GitHub and http://en.kedei.net/raspberry/raspberry.html

Hrmm.. I don"t think source is included. In the lcd_show_xx blobs are just kernels and modules, with a couple of very small scripts to copy the LED or HDMI kernel to the /boot place of the filesystem. (And no error checking, if you try copying the LED kernel, it backups the original kernel, but if you then run the copy-LED-kernel command again, it happily overwrites your original kernel, leaving you with two LED-enabled kernels and no original. hrrf..)

Well, I downloaded the whole 35MB .GZ file. Unpacked it and found 3402 .ko files. I presume that these are kernel object files. Nothing that looked remotely like source files for your TFT display.

Since the ILI9481 can be driven directly by SPI, this seems a crazy way to do things. Especially since a HC595 might be clockable at 100MHz but you need to wiggle all 24-bits. And an AVR can only manage 8MHz on a good day.

Not when you consider that once you have loaded an 18 bit colour all you need to do is toggle the T_CS pin at say 10MHz and you can load the same pixels sequentially at 10Mpixels/s (=180Mbps) i.e. clear the screen faster than it is refreshed. With SPI you have to keep serially sending the same pixel N bits of colour over and over again, which is very inefficient. In the worst case (where sequential pixels are different colours) the shift register still wins if you can clock it faster than an SPI link maximum rate (easy on higher performance computers) because the same number of bits need to be clocked whatever interface is used.

This suggests more control bit are shifted in than is actually needed, but my hunch of an 18 bit + control parallel interface to the TFT seems to be correct.

That aside, I sort of assume I"ll need a 3,3V logic converter, since the rpi has 3,3v GPIO pins and most arduinos have 5V? So I don"t accidentally burn out the display chips.

Yes, I expect that bodmer or myself could probably get you working if we made some inspired guessing with the schematic. You could always email Kedei and ask him for the genuine schematic. Make sure that you tell him the Revision number(s) on the pcb.

I had success with downloading Kedei"s 4GB images specific for the 6.1 board and putting on an SD card. Now the raspi boots up, and I see the boot messages scroll by. The original article said "expect about 6fps from the display" and that seems right - it"s jerky, but works.

I"m going to order a couple of logic level converters now (a pair of 74LVC245 should do nicely on a breadboard), and then I can poke at it from an arduino environment.

I"ve gotten the level converters now, and experimented a little, with no results but a plain white screen. I copied the "init commands" code from the Linux source for ILI9341, which are the closest thing I could see in the patch made by KeDei for any init-code, plugged an arduino Uno in via a level converter from 5v down to 3v3, with SCK/MOSI/MISO from arduino pins 13/12/11, and pin 9 to toggle L_CS, keeping it HIGH but pulling it LOW for 1 to 5 milliseconds after each 4-byte SPI write.

Eventually I tried without the level converter too, since the 74HC595 datasheet said it could handle "up to Vcc" on the input pins, Vcc being max 6V. But that was after trying a lot of combinations in the code; all the variations of SPISettings in Arduino"s SPI library, for transferring four bytes one at a time (someone else who also looked at these displays found out that the registers always want four bytes - and that the first byte is always 0x0 !). Also doing as you suggested with an extra "DC command bit" so that the "bytes" were 9-bits wide, ending in a zero bit to indicate "command". No luck, ah well.. And I can"t even be sure that either the display is an ILI9341 just because the sales page said so (others had gotten similar displays with another drive chip), or that the code in the kernel source matches this KeDei-version of the display.

This is a modified version of the official PJRC ILI9341_t3 library (https://github.com/PaulStoffregen/ILI9341_t3) to work with KeDei Raspberry Pi displays.

And it is always a Work In Progress. Also using a lot of work from the the Raspberry Pi implementation: https://github.com/cnkz111/RaspberryPi_KeDei_35_lcd_v62

This library was created to allow extended use on the KeDei Raspberry Pi display and supports T3.5, t3.6 T4 and beyond. It also has support for other T3.x boards as well as TLC.

Your SPI communications on this board does not go directly to display but instead go to three shift registers. There are also two SPI Chip select pins, one labeled, which looks like it is for the Display and the other looks like it is for the touch controller. This is partially true.

However the SPI communications with the display are a lot different than any other I have seen. For example there are no reset pins, nor a Data/Command(DC) pin. Instead this information is encoded into the SPI data that you send to the display.

We figured it out, as the RPI startup code, did several strange SPI transfers at the beginning, which appeared like they were directed to the XPT2046 Touch controller.

This library borrows some concepts and functionality from another ILI9341 library, https://github.com/KurtE/ILI9341_t3n. It also incorporates functionality from the TFT_ILI9341_ESP, https://github.com/Bodmer/TFT_ILI9341_ESP, for additional functions:

The teensy 3.6 and now 3.5 have a lot more memory than previous Teensy processors, so on these boards, I borrowed some ideas from the ILI9341_t3DMA library and added code to be able to use a logical Frame Buffer. To enable this I added a couple of API"s

Place the Adafruit_ILI9341 library folder your arduinosketchfolder/libraries/ folder. You may need to create the libraries subfolder if its your first library. Restart the IDE

However, Googling around I have found that some people were able to compile and install kernel drivers and it seems that some drivers are available from here: http://kedei.net/raspberry/raspberry.html

Now what happens... main HDMI screen cets coloured in four colors (red-yellow-blue-cyan), but SPI display started working. It shown four raspberry logos and a bunch of text, which ends with this line:

I also have one of these displays ("vision 1.0" ... damn they could not even spell version right in their first try), and I once tried the full image given by kedei ... it worked, but I was very sceptical, and finally I worked on some other projects.

If kedei is not giving any open source driver, then someone has to reverse-engineer the whole thing and write an open source driver on his/their own ...

That"s a very sensible approach - try and keep away from displays that need a custom OS in order to work. The tinylcd displays, at least the 3.5inch one anyway, have a fbtft overlay available by default in Raspbian - see for yourself in the /boot/overlays/ directory. You"ll still need to do other configurations, like console redirection, etc.

In this Arduino touch screen tutorial we will learn how to use TFT LCD Touch Screen with Arduino. You can watch the following video or read the written tutorial below.

For this tutorial I composed three examples. The first example is distance measurement using ultrasonic sensor. The output from the sensor, or the distance is printed on the screen and using the touch screen we can select the units, either centimeters or inches.

As an example I am using a 3.2” TFT Touch Screen in a combination with a TFT LCD Arduino Mega Shield. We need a shield because the TFT Touch screen works at 3.3V and the Arduino Mega outputs are 5 V. For the first example I have the HC-SR04 ultrasonic sensor, then for the second example an RGB LED with three resistors and a push button for the game example. Also I had to make a custom made pin header like this, by soldering pin headers and bend on of them so I could insert them in between the Arduino Board and the TFT Shield.

Here’s the circuit schematic. We will use the GND pin, the digital pins from 8 to 13, as well as the pin number 14. As the 5V pins are already used by the TFT Screen I will use the pin number 13 as VCC, by setting it right away high in the setup section of code.

I will use the UTFT and URTouch libraries made by Henning Karlsen. Here I would like to say thanks to him for the incredible work he has done. The libraries enable really easy use of the TFT Screens, and they work with many different TFT screens sizes, shields and controllers. You can download these libraries from his website, RinkyDinkElectronics.com and also find a lot of demo examples and detailed documentation of how to use them.

After we include the libraries we need to create UTFT and URTouch objects. The parameters of these objects depends on the model of the TFT Screen and Shield and these details can be also found in the documentation of the libraries.

So now I will explain how we can make the home screen of the program. With the setBackColor() function we need to set the background color of the text, black one in our case. Then we need to set the color to white, set the big font and using the print() function, we will print the string “Arduino TFT Tutorial” at the center of the screen and 10 pixels  down the Y – Axis of the screen. Next we will set the color to red and draw the red line below the text. After that we need to set the color back to white, and print the two other strings, “by HowToMechatronics.com” using the small font and “Select Example” using the big font.

Here’s that function which uses the ultrasonic sensor to calculate the distance and print the values with SevenSegNum font in green color, either in centimeters or inches. If you need more details how the ultrasonic sensor works you can check my particular tutorialfor that. Back in the loop section we can see what happens when we press the select unit buttons as well as the back button.

In order the code to work and compile you will have to include an addition “.c” file in the same directory with the Arduino sketch. This file is for the third game example and it’s a bitmap of the bird. For more details how this part of the code work  you can check my particular tutorial. Here you can download that file: