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ESP01 serial reception issue

PostPosted: Thu Jul 22, 2021 3:40 pm
by vdomos

I have 2 esp01 512k that I wanted to take out of the drawers to use with RPi Pico for example.
I flashed them all with 2 versions of the "Firmware AT COmmand".
I used the esptool tool with these 2 firmwares: **v0.9.2.2** and **v0.9.5.2**.

The programming of the ESP01s goes without problem and at reboot, I have a message from the tested firmware:

Code: Select all[System Ready, Vendor:www.ai-thinker.com]


Code: Select allAi-Thinker Technology Co. Ltd.

for the second one.

My problem is that I can't send AT commands to the ESP01 at all, none of them react with a linux serial terminal like *picocom* or the Arduino serial console.

I thought that the problem came from the firmwares but by testing a simple Arduino sketch for this type of board in the IDE, I have the same problem.

Code: Select alllong lastMsg = 0;
long now;
int incomingByte = 0;

void setup() {

void loop() {
  now = millis();
  if (now - lastMsg > 5000) {
    lastMsg = now;

  if (Serial.available() > 0) {
    Serial.print("I received: ");
    incomingByte = Serial.read();
    Serial.println(incomingByte, DEC);

In the console, I get the *now* variable displayed but no reaction when I send characters to it.

I use a personal card connected to a USB-serial card to program and test the esp01 like this without the DHT22:


What is strange is that the serial port of the 2 ESP01 works well in both directions when I flash it, I see the traffic on the LEDs of the USB-serial module. I don't understand why, it doesn't work anymore afterwards

Would you have an idea of the problem?

Thank you,

Re: ESP01 serial reception issue

PostPosted: Sat Jul 24, 2021 3:12 am
by vdomos
Well, it is solved simply by changing the USB-serial module still connected to my programmer board.
But I still wonder about the causes of non functioning especially since the flashing was going through this replaced USB-serial module without any problem.