Matrix 8x8 BiColor + esp8266: leds only light just after begin (solved)

Hello everyone.

I’m trying to control a 8x8 BiColor Matrix with a HT16k33 Led Backpack, and a Wemos D1 mini.
I haven’t found any post in this forum (or others) with the same problem and I’m starting to think that there is some problem with my led matrix or soldering.

The problem is that when I load the program / reset the board, I can see leds light up for only a few millis, and after that they don’t light up again.

I have tried examples and several codes and the behaviour is always the same.
This is my code (very simple):

#include <Wire.h>
#include <Adafruit_GFX.h>
#include "Adafruit_LEDBackpack.h"

Adafruit_BicolorMatrix matrix = Adafruit_BicolorMatrix();

void setup() {
  Serial.println("8x8 LED Matrix Test");
  // D1 IO, SCL GPIO5
  // D2 IO, SDA GPIO4
  matrix.begin(0x70);  // pass in the address

void loop() {
  matrix.drawPixel(random(0, 8), random(0, 8), LED_YELLOW);
  matrix.drawPixel(random(0, 8), random(0, 8), LED_GREEN);
  matrix.drawPixel(random(0, 8), random(0, 8), LED_RED);

If I add a 'matrix.begin(0x70) at the begining of the loop, I can see how leds ligth up for a few millis in every loop.

The circuit is also very simple:

Wemos Led Backpack
3v3 Vcc

I’m not using any resistor.

Thank you very much!

Wemos cannot power 128 leds from it's 3.3V pin.

The backpack needs minimum 4.5V.

If you power the backpack from 5V, it should have enough voltage and current. But there is a danger of damage to the wemos if you connect the i2c pins of a 5V device to a 3.3V device without level converters.

Thanks for the reply PaulRB.
I've tried the led matrix with an arduino mega and examples work perfectly.

I will try to power the backpack with 5v and add level converters 5 to 3.3v to avoid problems with wemos.

Thank you very much