Poor man's serial sniffer: reading Serial.print logs of an Arduino esp32 dev kit from another

Question

(I use ESP32 dev kits with Arduino api.)

My dev kit 1 is running my firmware; and I want to measure the current it draws, therefore I don't like to plug the USB in.

As I need to read the logs from the dev kit 1, I want to plug another dev kit that collects the log from the first through the UART.

The dev kit 1 firmware is as it is, but on the dev kit 2, I wrote such a thing:

#include <Arduino.h>
#include <Hardware.h>
HardwareSerial Reader();
void setup() {
 Serial.begin(115200);
 Reader.begin(115200, SERIAL_8N1, 16, 17); 
}
void loop() {
 while(Reader.available()) { 
 Serial.print(Reader.read());
 }
}

The wiring is as follows:

Dev kit 1	Wiring	Dev kit 2 (sniffer)
TXD	<=>	RXD (16)
RXD	<=>	TXD (17)
GND	<=>	GND

But this doesn't work, that is I can't see anything on the dev kit 2 serial on my computer. Any idea?

[UPDATE] As suggested by @juraj, I simply wire TX to TX, RX to RX and GND to GND and removed the Serial.begin(115200) from the firmware running on dev kit 1. Dev kit 2 firmware is as simple as:

void setup() {
 Serial.begin(115200);
 //Serial.printf("Serial2 logger RX (%d)<=>TX & TX(%d)<=>RX @ 115200 bauds", RX, TX); Serial.println();
}
void loop() {
 static unsigned lastHeartbeat = 0;
 const unsigned now =millis();
 if (now-lastHeartbeat > 4000) {
 lastHeartbeat = now;
 Serial.println("Heartbeat");
 }
}

Note that on dev kit 1, I commented out the line Serial.begin(115200).

No kit 1 logs appears on my computer.

The wiring of this setup:

enter image description here

• jsotola: But this doesn't work is not a useful description of any problem ... what were you expecting to happen? ... what actually happens?
• chrisl: As you just want to forward the serial data, don't use print() but write() in your sketch. Otherwise print() will interpret the data before sending and you just want to forward the raw data. With TXD and RXD I guess you mean (depending on the notation) TX0 and RX0 (or U0_TXD and U0_RXD), so GPIO1 and GPIO3 on the firmware board?
• Juraj: Serial.write(Reader.read());
• Juraj: if you just wire RX to RX and TX to TX the CH340 on the dev board will read it directly and send to USB. upload Blink or any other sketch without Serial.begin into the esp32
• Majenko: HardwareSerial Reader(); should be HardwareSerial Reader;

Answer 1

I finally managed to make it work.

The final wiring:

Kit 1	kit 2
The firmware to spy	The firmare that spys
RXD	17
TXD	16
GND	GND

The spying firmware uses Serial2

#define USE_READER true
#if USE_READER
#define USE_SERIAL2 true
#if USE_SERIAL2
 #define TX 17
 #define RX 16
 #define Reader Serial2
#else
 #include "SoftwareSerial.h"
 #define TX 12
 #define RX 13
 SoftwareSerial Reader;
#endif
#endif
void setup() {
 Serial.begin(115200);
#if USE_READER
 Serial.printf("Serial logger RX (%d)<=>TX & TX(%d)<=>RX @ 115200 bauds", RX, TX); Serial.println();
 #if USE_SERIAL2
 Reader.begin(115200);
 #else
 Reader.begin(115200, SWSERIAL_8N1, RX, TX, false);
 #endif
 #endif
}
void loop() {
 static unsigned lastHeartbeat = 0;
 const unsigned now =millis();
 if (now-lastHeartbeat > 4000) {
 lastHeartbeat = now;
 Serial.println("Heartbeat");
 }
 #if USE_READER
 if (Reader.available()) {
 
 Serial.write(Reader.read()); 
 }
 else {
 #endif
 
 //Serial.print(".");
 delay(500);
 
 #if USE_READER
 }
 #endif
}

The spied firmware

You leave it as it is. Don't remove Serial.begin(115200);.

The breadboard photo:

enter image description here