Hi all,
I have bought a ILI9225 2.0" TFT display (8 pin version) and have a problem when using the Nkawu library and SPI hardware. The display works nice using software SPI. SPI hardware does not work. Using the Basic Demo code included in the examples, I noticed that chosing different TFT_brightness have an extrange effect in the pixels drawn. High values (>200) give the screen completely white. However, lower values (<100) start to draw pixels in the screen but the higher this value, the more pixels are missing in the image.
I also tried to put TFT_LED=0 and connect the LED pin directly to +5V, but the display remains white.
Could anyone made this display working with hardware SPI?
Thank you and regards,
Andrew
What 8-pin version? The regular ILI9225 SPI board as pictured on Nkawu's Github library has got 11 pins. And an unmounted 5-pin for the SD / Flash chip.
Both software SPI and hardware SPI work fine.
My board has an LED pin.
Other boards have NC.
I have always used on/off for the LED. I can see little point in altering the backlight other than on or off.
David.
This is the version I got in ebay. It seems a similar board with the same controller, but I don't know whether there are any other difference...
Ah-ha. I have never seen that one before. I do not believe the printed messages.
There is no sign of any LDO regulator i.e. 5V to 3.3V
There is no sign of any level-shifters i.e. no resistors, no integrated circuits, ...
Open-Smart generally provide schematics for their products. Ask them. It might be that there are chips soldered on the other side of the pcb.
Meanwhile, I would use 3.3V power and 3.3V Logic to be on the safe side.
Mr Nkawu's library should work fine with 3.3V logic.
Please let us know how you get on with the schematic. TFT controllers are not 5V tolerant.
It is misleading for Ebay Vendors to say otherwise but they probably do not know what they are selling.
It is dishonest for a Manufacturer like Open-Smart. They do know what they are doing.
David.
Thank you for your reply.
I asked the seller for the schematic, and they sent me it. In the schematic, there is a level converter and a DC-DC linear regulator in the 5V version. I guess these component are below the display so they are not visible in the PCB.
I am thinking that the problem could be the display unit (faulty), because they sent me the same libraries I am currently using and a video showing how the display works. However, still very strange. UTFT library works, although very slow (I think they use software SPI)
Do you know whether UTFT libraries use hardware SPI?
Thank you very much,
Please attach the schematic that they sent to you.
UTFT has no concept of hardware SPI or even a bus.
David.
Hello again.
Finally, I found the problem!
In the code snippet supplied as example for testing the TFT, it is indicated to connect the LED line directly to 5V in the case that no bright control is used. For some reason, feeding the LED line with more than 1.5V (including the PWM output used for bright control) causes malfunction in the display. Thus, I used a simple voltage divider (3K3 + 1K2) to reduce the voltage in the LED line to about 1.3 V. Now the display works.
You can find attached the schematic the seller sent me.
Regards,
TFT 2.0 SPI 5V_3V3 Schematic.pdf (22.7 KB)
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From your schematic R1, Qi control the Backlight LEDs.
Since R1 is 1k0 I can see no problem with connecting to 1.3V or 5V.
With 5V base current is 4.5mA
With 1.3V base current is 0.8mA
Typical LED current for this sort of display is 50mA.
Q1 will saturate with 0.8mA and with 4.5mA.
I would prefer a small resistor to limit the LED current to 50mA e.g. 2R2 or 3R3 in the Q1 collector line..
Anyway, I am pleased that you are operational now.
David.
Thank you, David.
Putting a series resistor to limit the led current was the first thing I tried without success... Actually, the solution does not make sense to me too, according to the schematic. Anyway, the current used to feed the led shouldn't affect the bus signals.
Regards and thank you for your help.
A.
Please attach or link to the schematic.
And if possible a photo of the edge of the pcb so you can see the gap between pcb and TFT panel.
The panel is normally mounted with double sided foam tape. There will be gaps where you can see if there are any SMT components on the underside of the pcb. Ignore the SMT components mounted on the flexi ribbon.
I doubt if you can get a good photo. But you can use a torch to shine in the gap and make your own investigation.
David.
