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Thread Contributor: raufjay[SOLVED] Reset Power up issue with HOTMMCU FT811CB

I got 4x FT811CB,  5" with capacitive touch from the HOTMCU.

The screen is working ok. But there is a problem.
When we reset or re-power, screen is just blank, then we have to touch or move a little the wires on the screen. Then screen starts up.

We tried many many times, with shortest wires of just 7cm. We tried with the FTC connector/wire which came alongwith the LCD, we tried with 10pin IDC cable/connector, we tried with single/one by one cable with the same result. 

We tried with many different controller boards, with different reset schemes.

Please do let us know how to overcome this issue.

Does any of you have any such issue? or can suggest me what are we doing wrong.
I have total 5 screens, 4x FT811CB and one is FT800CB 4.3". The 4.3" with FT800 is working fine and does not have this problem. But all 4 FT811CB 5" has the same issue.


I got the following reply from hotmcu tech support.

The solution:
First, reduce the SPI clock frequency. Or
Second, remove the R4 resistor.

I tried reducing the SPI in GD2UB.cpp from 10500000 to 3000000. No difference.
I have commented the original line in GD2UB.cpp and added a new line with spiclock changed.
SPISettings settingsSTM32(FreqSPI1, MSBFIRST, SPI_MODE0);
//SPISettings settingsSTM32(FreqSDIO, MSBFIRST, SPI_MODE0);

In GD2UB.h the FreqSPI1 = 3000000

Can you please guide me on it.

I havent found the R4 resistor on the pcb. I think that is on other side of the pcb. I will try finding that out.


Hi thanks.

Resistor R4 be line MISO chip FT811Q below the circuit. Pull-UP resistor

I removed the R4 but it still has same problem. I have to touch the cables or move it a little bit. otherwise lcd does not come up.


Thanks you @ raufjay !!!

This location R4 to HOTMCU screen;


Thank you for sending the photoes. I have already tried by removing R4 which is of 47K. But my problem is still not resolved. When I reset then screen does not come up unless i touch the wires. when I re-power the same thing. But if I turn it off and wait for 10 seconds or more and then turn it ON, it comes up with no problem.

Meanwhile I received the following message from hotmcu.
Dear Sir or Madam
   We tested one by one before shipment. So i think this is your lcd driver problem. I send my driver to you.
The files they refereing are for arduino. Not for stm32. it does not compile with stm32 board selected.

I saw you sent two pictures. One shows R4 but other one shows two wires jumping from invertor circuit. What are these two jump wires for?

For my issue, I think there might be some reset issue. Meanwhile I realized PB1 in your GD2UB.h used for POR. I read at that PB1, PB8 and PB9 will not work as PWM output, though they are PWM but in board file of maple they are not configured as PWM.

I tried using FT811CB lcd with my system reset, with PB1 and with PA8. I changed POR assignment from PB1 to PA8 in GD2UB.h file. But with no luck.

Any further idea?


Better response on post RE: Reset Power up issue with HOTMMCU FT811CBHello,

Finally the problem resolved.

My circuit is working on 3.7v lipo battery. FT811CB 5" LCD has 2x 74125 logic converters. Because FT811CB was also intended to use with 5volt interface like arduino uno or mega.
I just had to add 3x 10k pullup resistors to MOSI,MISO and CLK at my STM32103 based board.
Adding these 10k pullup resolved the issue. And now LCD turns on as soon as power ups or resets.
Thank you for your support.
P.S. Later I had to add 1x 10k pullup to CS or SS which was PA4 in my project. So whoever has this issue, I would suggest to add 4x 10K pullups to all 4 lines, i.e. MOSI, MISO, CLK and SS.
Thanks @ raufjay

Nice. I maked theard important.  Gracias

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