LCD display Issues

[sabu31]

Dear All,

I am using an LCD circuit along with power supply circuit.
The LCD is used to display pwm and duty ratio related parameters. Initially, when power output is low the display is working fine.
When the power supply is gradually increased to 100V. The LCD display gets corrupted. The ESP32 microcontroller will communicate LCD using I2C.
What could be the solution to overcome this display problem . I tried using an isolator circuit as an interface between the display and microcontroller but this led to the display not showing the correct value even when the power output is low. I am attaching the circuit for your reference. Is there any problem in the isolator circuit? What else can be done to resolve this LCD issue.

 

[andre_luis]

I tried using an isolator circuit as an interface between the display and microcontroller

No, don't ever put anything between I2C and microcontroler. You are dealing with low level, high impedance signals, keep in mind that I2C buses are intended to be used at the same board. In addition, there is no decoupling ceramic capacitors at the power bus.

 

[danadakk]

Your schematic shows two different ground systems/symbols, nowhere do I see
them connected together....? So you have a common mode issue, or at minimum
its leakage altering your logic levels to display.....


Regards, Dana.

 

[KlausST]

Hi,

Your schematic shows two different ground systems/symbols, nowhere do I see
them connected together....?

That´s basically the idea of using a digital isolator.

@OP:
But this digital isolator is not suitable for I2C signals.
I2C signals are driven by open_collector outputs in combination with a pull up. And they are used for bidrectional signaling.

Regarding the communication problem:
It´s either induced noise, or power supply noise.
We need to know:
* display type and complete schematic
* wiring (best a photo <100kBytes)
* I2C clock frequency
* display data update rate
* your code

Klaus

 

[danadakk]

Digital isolators for SPI and I2C, attached.

Part OP uses in schematic never mentions I2C in its datasheet.


Knight

 

[pjmelect]

The fact that the display is faded in the second photo, means that there is a supply problem to the display, the fading of the display has nothing to do with the communication to the display.

 

[sabu31]

The fact that the display is faded in the second photo, means that there is a supply problem to the display, the fading of the display has nothing to do with the communication to the display.

Thanks for the hint. I used bulk capacitor and bypass capacitor (10uF and 0.1uF) at the LCD 5V input side and also wound the connecting wire across the toroidal ferrite core (around 4 turns). Also put a small film capacitor in dc output of my power supply. The combination of all these held to prevent the display issue upt 220V input ac.

 

[pjmelect]

You only need a reduction of around a couple of hundred milivolts on the 5V of the display to cause fading.