ESP32: manage multiple Serial and logging for debugging – 3

by Renzo Mischianti · Published 20 September 2020 · Updated 1 December 2021

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ESP32 multiple Serial UART and Logging levels

As you can see in the pinout diagram esp32 can have multiple UART, some are market as RX2 and TX2.

You can find ESP32 used for this test on AliExpress ESP32 Dev Kit v1 - AliExpress selectable - AliExpress TTGO T-Display 1.14 ESP32 - AliExpress NodeMCU V3 V2 ESP8266 Lolin32 - AliExpress WeMos Lolin32 CP2104 CH340 - AliExpress ESP32-CAM programmer - AliExpress ESP32-CAM bundle - AliExpress ESP32-WROOM-32 - AliExpress ESP32-S

We are going to see an ESP32 DOIT DEV KIT v1

And a better ESP32 the WeMos LOLIN32.

This pins can be used at to transmit core debug information or like a classic serial named Serial2.

To connect, naturally, you must use a USB to TTL converter, you can find it at 1$.

Exists more expensive FT232RL or FT232 module, but a CH340G or CH340 working very good.

You can find here AliExpress USB to TTL CH340G - AliExpress USB to TTL FT232RL

Connection schema is very simple, here for DOIT DEV KIT v1

esp32 DOIT DEV KIT v1 Serial2 UART2 ttl to usb schema

and here for WeMos LOLIN32

esp32 WeMos LOLIN32 Serial2 UART2 ttl to usb schema

Example

/*
 *  ESP32 DOIT DEV KIT v1 - ESP32 WeMos LOLIN32
 *  Debug on standard Serial and Serial2 on GPIO17 pin
 *  by Mischianti Renzo <https://mischianti.org>
 *
 *  https://mischianti.org/
 *
 */
#include "Arduino.h"

void setup()
{
	Serial.begin(9600);
	Serial2.begin(9600);
}

int i = 0;
void loop()
{
	i++;
	Serial.print("Hi, I'm Serial on standard TX RX pin! --> ");
	Serial.println(i);
	Serial1.print("Hi, I'm Serial2 on GPIO17! --> ");
	Serial1.println(i);
	delay(1000);
}

Here the serial monitor on standard UART (USB connection).

Hi, I'm Serial on standard TX RX pin! --> 1
Hi, I'm Serial on standard TX RX pin! --> 2
Hi, I'm Serial on standard TX RX pin! --> 3
Hi, I'm Serial on standard TX RX pin! --> 4

Here the serial monitor on Serial2 (USB to TTL converter).

Hi, I'm Serial1 on GPIO17! --> 1
Hi, I'm Serial1 on GPIO17! --> 2
Hi, I'm Serial1 on GPIO17! --> 3
Hi, I'm Serial1 on GPIO17! --> 4

Core debug

You can activate in Tools --> Debug level the logging at build time. This flag can activate low level system file and library log, the level are

None
Error
Warn
Info
Debug
Verbose

I write they in hierarchical order, so if you select None, no logs are shows, if you select Verbose all logs are shows.

But set the core Debug Level is not sufficient you must enable log on your serial:

Serial2.setDebugOutput(true);

And you can use the core debug level for your project also, the commands are one for every log level:

	log_v("Verbose");
	log_d("Debug");
	log_i("Info");
	log_w("Warning");
	log_e("Error");

Than here a simple sketch to test they:

/*
 *  ESP32 DOIT DEV KIT v1 - ESP32 WeMos LOLIN32
 *  Debug on standard Serial and Serial2 on GPIO17 pin
 *  And logging on Serial2
 *  You must set log level on option of your IDE
 *  by Mischianti Renzo <https://mischianti.org>
 *
 *  https://mischianti.org/
 *
 */
#include "Arduino.h"
#include <WiFi.h>

#define STA_SSID "<YOUR-SSID>"
#define STA_PASS "<YOUR-PASSWD>"

#include "esp32-hal-log.h"

void setup() {
	Serial.begin(9600);
	Serial2.begin(9600);
	Serial2.setDebugOutput(true);

	Serial2.println("START WIFI");
	WiFi.begin(STA_SSID, STA_PASS);

    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial2.print(".");
    }

    Serial2.println("");
    Serial2.println("WiFi connected");
    Serial2.println("IP address: ");
    Serial2.println(WiFi.localIP());
    delay(1000);
}

int i = 0;
void loop() {
	i++;
	Serial.print("Hi, I'm Serial on standard TX RX pin! --> ");
	Serial.println(i);
	delay(100);
	Serial2.print("Hi, I'm Serial2 on GPIO17! --> ");
	Serial2.println(i);
	delay(1000);

	log_v("Verbose");
	log_d("Debug");
	log_i("Info");
	log_w("Warning");
	log_e("Error");
	delay(5000);
}

Than if you compile and upload the sketch with log level set to Info you obtain this result on Serial and Serial2

START WIFI
.
WiFi connected
IP address:  
192.168.1.168
Hi, I'm Serial on standard TX RX pin! --> 1 
Hi, I'm Serial2 on GPIO17! --> 1
[I][esp32_serial_serial2_log_test.ino:50] loop(): Info
[W][esp32_serial_serial2_log_test.ino:51] loop(): Warning
[E][esp32_serial_serial2_log_test.ino:52] loop(): Error
Hi, I'm Serial on standard TX RX pin! --> 2 
Hi, I'm Serial2 on GPIO17! --> 2
[I][esp32_serial_serial2_log_test.ino:50] loop(): Info
[W][esp32_serial_serial2_log_test.ino:51] loop(): Warning
[E][esp32_serial_serial2_log_test.ino:52] loop(): Error

But if you upload sketch with Verbose:

START WIFI
[D][WiFiGeneric.cpp:337] _eventCallback(): Event: 0 - WIFI_READY
[D][WiFiGeneric.cpp:337] _eventCallback(): Event: 2 - STA_START
[D][WiFiGeneric.cpp:337] _eventCallback(): Event: 4 - STA_CONNECTED
[D][WiFiGeneric.cpp:337] _eventCallback(): Event: 7 - STA_GOT_IP
[D][WiFiGeneric.cpp:381] _eventCallback(): STA IP: 192.168.1.168, MASK: 255.255.255.0, GW: 192.168.1.1
.
WiFi connected
IP address: 
192.168.1.168
Hi, I'm Serial on standard TX RX pin! --> 1 
Hi, I'm Serial2 on GPIO17! --> 1
[V][esp32_serial_serial2_log_test.ino:48] loop(): Verbose
[D][esp32_serial_serial2_log_test.ino:49] loop(): Debug
[I][esp32_serial_serial2_log_test.ino:50] loop(): Info
[W][esp32_serial_serial2_log_test.ino:51] loop(): Warning
[E][esp32_serial_serial2_log_test.ino:52] loop(): Error
Hi, I'm Serial on standard TX RX pin! --> 2 
Hi, I'm Serial2 on GPIO17! --> 2
[V][esp32_serial_serial2_log_test.ino:48] loop(): Verbose
[D][esp32_serial_serial2_log_test.ino:49] loop(): Debug
[I][esp32_serial_serial2_log_test.ino:50] loop(): Info
[W][esp32_serial_serial2_log_test.ino:51] loop(): Warning
[E][esp32_serial_serial2_log_test.ino:52] loop(): Error

You can see that there are WiFi low level debug [D] log also, this because are set on WiFi library.