STM32L100C-DISCO odd LCD issue

[bob jones]

Posted on April 07, 2018 at 08:19

Hello, So I am using a STM32L100C-DISCO to display some numbers on an LCD display, I am using the LSI as the clock source. My program works fine for a couple of hours, but if I de-power then power-on the board, the LCD booster circuit does not turn on. I thought this might be a board malfunction because of me blowing it up, but everything else works. I then bought another of the exact same board and tried it. Does the exact same thing as the first board. But now if I leave the first board unplugged for a couple of hours the LCD booster circuit on the that powers on, and my program works fine. I tried this with the second board but with it still plugged into the LCD but with no power, and the booster circuit wont start up. I have no explanation for this. I am using AC6 with the latest firmware.

thanks

#lcd #stm32l1 Note: this post was migrated and contained many threaded conversations, some content may be missing.

[waclawek.jan]

Posted on April 08, 2018 at 00:21

What LCD? What booster circuit? Why do you think this is STM32-related?

JW

[T J]

Posted on April 08, 2018 at 00:59

sounds like the LCD backlight,

do you have a dimmer function ?

[bob jones]

Posted on April 08, 2018 at 07:01

The LCD booster circuit is meant to control the contrast of the LCD, it also acts as the power supply for the LCD. But I dont have a function for this, the contrast is automatically set in the CubeMx setup

[bob jones]

Posted on April 08, 2018 at 07:02

because the LCD booster circuit is inside the stm32 microcontroller

[waclawek.jan]

Posted on April 08, 2018 at 09:55

You mean the Step-Up converter mentioned in RM0038 16.4.5  Voltage generator chapter?

There is no LCD on the STM32L100C-DISCO so it's something you've connected to it. What display is it and how did you connect it?

JW

[bob jones]

Posted on April 08, 2018 at 10:22

Hello, I think so?, the manual I have say the built in LCD voltage generator, the LCD im using this: 

https://docs-apac.rs-online.com/webdocs/144d/0900766b8144dacf.pdf

 , I have just connected all pins from the LCD directly to the board, do I need a resistor?

thanks

[waclawek.jan]

Posted on April 08, 2018 at 10:42

Oh, but that's a 5V display... How did you connect the COM pins?

JW

[bob jones]

Posted on April 08, 2018 at 10:45

I connected the com pin of the LCD directly to the com pin of the board, I assumed that the power was supplied from the com pin

[waclawek.jan]

Posted on April 08, 2018 at 11:06

That's correct. However, given the display is 5V according to its datasheet, I still wonder how comes it works at all, given STM32L1xx's output voltage is max. 3.6V.

You are supposed to have a capacitor connected to the VLCD pin, have you? See datasheet for details. Then measure voltage on that pin. Better yet, get an oscilloscope and observe the waveforms on COM and a 'lit' SEG pin.

JW