Troubles getting ST7735 Display to work

[Alworx]

Hi @all,
title says it all - I'm having troubles at getting a ST7735-based 1.8" display to work.
Sometimes it stays black, sometimes it shows the start screen, but very dark and freezed.
I'd assume it's underpowered, but not entirely sure...

When measuring voltage with a standard multimeter I'm getting following results:

LCD VCC: 5V
LED: 2.5V
Reset: 3.3V
CS: 0V

I've attached a photo of the display when showing the start screen (that stays freezed).

Thanks & cheers, Andi

edit:
Mixed up the measurements, now corrected.

[ignotus]

Why do you say it freezes? Won't it scroll through the menu when you press the buttons? The screen doesn't exit to just a vu meter screen like the old one, it stays where it is when you turn it on or where you leave it when scrolling through the menu.

Also, when you turn it on and it's black, try pressing the 'up' button to see if it's because the contrast is down. I had this issue where upon turning the module on it was always black, and I had to press the up button to get the contrast back. I don't know what caused it but it stopped happening a while ago.

[dmitri]

Did you connect pins 13&14 of the LCD connector with a resistor? Is the connection good? What is the value of the resistor as measured by a meter? If the value is too high or the connection is flaky, on power up MegaDrum will think a standard LCD is connected so the color LCD will stay black. A too low value of the resistor can damage these pins when in a bootloader mode during firmware upgrade.

Note, the above is true for STM32F205 based MegaDrum built pre-November 12 2015. STM32F205 based MegaDrum built after that can have pins 13 and 14 of the LCD connector shorted with a jumper.

[dmitri]

Also, if it is an STM32F205 based MegaDrum built pre-November 12 2015, then you may need to replace the resistor circled in the photo with a 200 Ohm resistor otherwise the LCD will be too dim:

pc-backlight.png

[Alworx]

Why do you say it freezes? Won't it scroll through the menu when you press the buttons?

Exactly, no scrolling and the meters don't move either.

Also, when you turn it on and it's black, try pressing the 'up' button to see if it's because the contrast is down. I had this issue where upon turning the module on it was always black, and I had to press the up button to get the contrast back.

I tried, without success. Didn't expect contrast adjustments to work with the graphic display, though...

Did you connect pins 13&14 of the LCD connector with a resistor? Is the connection good? What is the value of the resistor as measured by a meter?

Yes, measured 216 Ohm. Suspected this too and tried a Poti set to 200 Ohm, but that didn't change anything.

Also, if it is an STM32F205 based MegaDrum built pre-November 12 2015, then you may need to replace the resistor circled in the photo with a 200 Ohm resistor otherwise the LCD will be too dim:

Ok, didn't know that. I guess i shouldn't connect the old display after that modification anymore?

Thanks 4 supporting

[dmitri]

Why do you say it freezes? Won't it scroll through the menu when you press the buttons?

Exactly, no scrolling and the meters don't move either.

Is it the whole MegaDrum or just the LCD which freezes? If MDM can still talk to MegaDrum then it is just the LCD which freezes and as far as I can see it can only mean two things:
1. There is an intermittent wiring problem between the board.
2. The LCD itself has a problem.

Also, when you turn it on and it's black, try pressing the 'up' button to see if it's because the contrast is down. I had this issue where upon turning the module on it was always black, and I had to press the up button to get the contrast back.

I tried, without success. Didn't expect contrast adjustments to work with the graphic display, though...

With ST7735 it adjust brightness.

Did you connect pins 13&14 of the LCD connector with a resistor? Is the connection good? What is the value of the resistor as measured by a meter?

Yes, measured 216 Ohm. Suspected this too and tried a Poti set to 200 Ohm, but that didn't change anything.

Also, if it is an STM32F205 based MegaDrum built pre-November 12 2015, then you may need to replace the resistor circled in the photo with a 200 Ohm resistor otherwise the LCD will be too dim:

Ok, didn't know that. I guess i shouldn't connect the old display after that modification anymore?

You can still connect the old LCD, it'll just have higher contrast then before.

[Alworx]

Why do you say it freezes? Won't it scroll through the menu when you press the buttons?

Exactly, no scrolling and the meters don't move either.

Is it the whole MegaDrum or just the LCD which freezes? If MDM can still talk to MegaDrum then it is just the LCD which freezes and as far as I can see it can only mean two things:
1. There is an intermittent wiring problem between the board.
2. The LCD itself has a problem.

MegaDrum talks and works, setting brightness of the display works too (i didn't recognize this last time - maybe I muddled with the left/right encoder before pressing up/down @ignotius).
I'll give it one last shot and rewire the display on the weekend, otherwise I'll just stick to the old display. Better for my not-so-good eyes anyway

Thanks one more time for your help dimitri and ignotius!

[dmitri]

Also, when you turn it on and it's black, try pressing the 'up' button to see if it's because the contrast is down. I had this issue where upon turning the module on it was always black, and I had to press the up button to get the contrast back. I don't know what caused it but it stopped happening a while ago.

I just released a new firmware version which deals with backlight level on different types of ST7735. It now covers backlight ranges for all ST7735 types but if set too low the LCD may appear black/not working. To indicate that the LCD is ok, the backlight is set to maximum at power up and after ~3s it is set to a saved configured level.

[Alworx]

I just released a new firmware version which deals with backlight level on different types of ST7735. It now covers backlight ranges for all ST7735 types but if set too low the LCD may appear black/not working. To indicate that the LCD is ok, the backlight is set to maximum at power up and after ~3s it is set to a saved configured level.

Thanks, feels like a firmware dedicated to me

In the meantime I've checked my connections to the display and exchanged the proposed resistor from 1k to 220 for more brightness.

The problem persists, but now it's somehow reproducable:

- when switched off and switched on again after some seconds, the display most of the time stays black
- when switched off and then on quickly again it works every time, but only for some seconds. Then it freezes, sometimes inbetween refreshing

I've uploaded a video on youtube showing that behaviour: https://www.youtube.com/watch?v=qf_xHAHTlbY

I would suspect the display detection routine at startup failing, but that wouldn't explain the freezes i guess?

After all, there's good news too - Megadrum showed its soft heart at a freeze (see the photo attached)

[dmitri]

I would suspect the display detection routine at startup failing, but that wouldn't explain the freezes i guess?

Exactly. If it freezes after awhile means startup detection has nothing to do with it. The fact that you can actually adjust brightness when the LCD freezes again confirms that MegaDrum continues to function properly. If you're sure about the LCD wiring I can only suspect that the LCD is not good.
I've already built dozens of MegaDrum modules/kits with color LCDs and none of them had shown any problems.