LVGL and displaying data sent from COM Ports?

How-to
1

Hey there, I’m trying to send data via my COM port over my usb to my esp32-s3 and have that data be displayed on a LVGL button. Though when i send the data the display turns black. I know its the data sending that’s doing this because i can add functionality to change the buttons text when i trigger a defined piece of code. But this is not what i want. I want to get data from spotify api ( already got the spotify api data figured out ) and send it over my usb to my esp32 for it to be display. Ex: The title of the current playing song being displayed on a button.
Any help regarding why my display is turning off when i receive data on my esp32-s3 would be greatly appreciated. I haven’t configured the displaying of the data yet. Just trying to receive data to the esp32 without it blacking out. I’ll provide my code now.

ESP32-S3 CODE

import time
import os
import sys
import select
from machine import Pin
import lvgl as lv
from display_driver import disp, disp_drv

led = Pin(2, Pin.OUT)  # Adjust GPIO number if needed
MAX_LOG_SIZE = 10 * 1024  # 10 KB

# ====== Input loop setup ======
poll = select.poll()
poll.register(sys.stdin, select.POLLIN)

# Create screen
scr = lv.obj()

# Colors
spotify_green = lv.color_hex(0x1DB954)
spotify_dark = lv.color_hex(0x191414)
spotify_light_gray = lv.color_hex(0xB3B3B3)
white = lv.color_hex(0xFFFFFF)

# Create styles
style_bg = lv.style_t()
style_bg.init()
style_bg.set_bg_color(spotify_dark)
style_bg.set_border_width(0)

style_green_bg = lv.style_t()
style_green_bg.init()
style_green_bg.set_bg_color(spotify_green)
style_green_bg.set_radius(8)

style_white_text = lv.style_t()
style_white_text.init()
style_white_text.set_text_color(white)

style_light_gray_text = lv.style_t()
style_light_gray_text.init()
style_light_gray_text.set_text_color(spotify_light_gray)

style_progress_bg = lv.style_t()
style_progress_bg.init()
style_progress_bg.set_bg_color(lv.color_hex(0x333333))
style_progress_bg.set_radius(4)

style_progress_indic = lv.style_t()
style_progress_indic.init()
style_progress_indic.set_bg_color(spotify_green)
style_progress_indic.set_radius(4)

# Apply screen background style
scr.add_style(style_bg, 0)

# Album art box (placeholder)
album_art = lv.obj(scr)
album_art.set_size(80, 80)
album_art.add_style(style_green_bg, 0)
album_art.align(lv.ALIGN.TOP_MID, 0, 20)

# Song title label
song_title_label = lv.label(scr)
song_title_label.set_text("Blinding Lights")
song_title_label.add_style(style_white_text, 0)
song_title_label.align_to(album_art, lv.ALIGN.OUT_BOTTOM_MID, 0, 10)

# Artist label
artist = lv.label(scr)
artist.set_text("The Weeknd")
artist.add_style(style_light_gray_text, 0)
artist.align_to(song_title_label, lv.ALIGN.OUT_BOTTOM_MID, 0, 5)

# Progress bar
progress = lv.bar(scr)
progress.set_size(200, 10)
progress.add_style(style_progress_bg, lv.PART.MAIN)
progress.add_style(style_progress_indic, lv.PART.INDICATOR)
progress.set_range(0, 100)
progress.align_to(artist, lv.ALIGN.OUT_BOTTOM_MID, 0, 15)

# Play button
btn = lv.button(scr)
btn.set_size(120, 40)
btn.align(lv.ALIGN.BOTTOM_MID, 0, -20)
btn.add_style(style_green_bg, 0)

btn_label = lv.label(btn)
btn_label.set_text("Next In Queue: ")
btn_label.add_style(style_white_text, 0)
btn_label.center()

# Load screen
lv.screen_load(scr)

# Logging function
def send_log(msg):
    try:
        if 'debug_log.txt' in os.listdir() and os.stat('debug_log.txt')[6] > MAX_LOG_SIZE:
            open('debug_log.txt', 'w').close()  # Clear if too large
        with open('debug_log.txt', 'a') as f:
            f.write(msg + '\n')
    except Exception as e:
        print("Logging error:", e)


# Main loop
while True:
    lv.task_handler()
    time.sleep_ms(10)
    try:
        events = poll.poll(100)  # 100ms timeout
        if events:
            line = sys.stdin.readline().strip()
            send_log(f"Received input: {line}")

            if line == "start":
                with open('Startlog.txt', 'a') as f:
                    f.write("ESP32 Received right data.\n")
                send_log("RIGHT")
            else:
                with open('Startlog1.txt', 'a') as f:
                    f.write("ESP32 Received wrong data.\n")
                send_log("WRONG")

            # Blink LED
            led.on()
            time.sleep(0.2)
            led.off()
        else:
            time.sleep(0.05)  

    except Exception as e:
        send_log(f"Input error: {e}")

PC Code to send data via usb

import serial
import time

# === CONFIGURATION ===
COM_PORT = 'COM9'          
BAUD_RATE = 115200
DATA_TO_SEND = "start\n"   

# === OPEN SERIAL CONNECTION ===
try:
    ser = serial.Serial(COM_PORT, BAUD_RATE, timeout=1)
    time.sleep(2)  # Give ESP32 time to boot and get ready

    print(f"Sending to ESP32: {DATA_TO_SEND.strip()}")
    ser.write(DATA_TO_SEND.encode())

    # Wait and read any response
    time.sleep(0.2)
    response = ser.read_all().decode().strip()
    if response:
        print("ESP32 says:", response)

    ser.close()
except Exception as e:
    print("Serial communication error:", e)

I do get a psram error when i start the program to test the lvgl UI on thonny but none-the-less it continues so it never really bothered me due to the fact that this is the only working firmware with lvgl i’ve found for my esp32-s3 . ( NOTE: I cannot send data while having thonny open so this is purely to test for lvgl errors, Explained at the end of this thread )

ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0x1 (POWERON),boot:0x8 (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fce3820,len:0x105c
load:0x403c9700,len:0x4
load:0x403c9704,len:0xbd8
load:0x403cc700,len:0x2e34
entry 0x403c989c
E (437) quad_psram: PSRAM ID read error: 0x00ffffff, PSRAM chip not found or not supported, or wrong PSRAM line mode
E (437) esp_psram: PSRAM enabled but initialization failed. Bailing out.

That error message could be getting displayed every time i receive data to the esp32-s3 which could be the root cause but no way of telling because i can’t send data over com9 while having thonny open on com9, Both get conflicted and one doesnt work. I have to have the script for the lvgl code on main.py so it runs without thonny open.
Thanks again for any help!

2

UPDATE: Out of some miracle i figured it out. I was taking a peek at my board and realized it has 2 usb hubs and just plugged 2 usbs in so i have 2 com ports. One is for lvgl i guess and the other is used for data! Now it doesnt crash and i can update my screen ui based on data i send!

3

Thanks a lot for sharing your solution! I was running into a very similar issue. my display would go black whenever I tried to receive data over USB, and I couldn’t figure out why. After reading your update about the two USB interfaces on the board and using one for LVGL and the other for data, I tried the same and it works perfectly now.

You really helped me out. Appreciate it! :raised_hands:

4

Oh! That’s great to hear! I struggled for days trying to figure it out! Glad i could help out!!!