ESP send string to Arduino

Question

I'm trying to send a string from an ESP32 to an Arduino. I'm using a level shifter, where the Uno is now the Mega (since I couldn't get the Uno to work).

RX0 is now RX1, connected to UART2 of ESP32.

// Master sender ESP32

#include <HardwareSerial.h>
 
void setup() {
  // Serial.begin(115200);
  Serial2.begin(9600, SERIAL_8N1, 16, 17);
  delay(100);
}
    
void loop() {
  String shape = "1,2,3";
  Serial2.println(shape);
  delay(500);
}

//Receiver Mega

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  Serial1.begin(9600);
  Serial.begin(19200);
  delay(100);
}

void loop() {
  if (Serial1.available()) {
    String received = "";
    received = Serial1.readString();
    Serial.println(received);
  }
}

Is there something in either sketch that should be changed?

did you connect the correct pins? ... do not use pin 0 and pin 1 for software serial — jsotola
– jsotola, Commented Jan 27, 2021 at 22:24
@jsotola In this setup, I'm not using software serial. The pinout is displayed with the exception of RX0 now being RX1 on the Mega. — Adamelli
– Adamelli, Commented Jan 27, 2021 at 22:34
are you missing the GND connection of the LV side of the level shifter? — hcheung
– hcheung, Commented Jan 28, 2021 at 13:28

Adamelli · Accepted Answer · 2021-01-28 20:22:55Z

readStringUntil('\n')

//Receiver Mega

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  Serial1.begin(9600);
  Serial.begin(19200);
  delay(100);
}

void loop() {
  if (Serial1.available()) {
    String received = "";
    received = Serial1.readStringUntil('\n');
    Serial.println(received);
  }
}

It's about how Serial.readString() works: it reads from the serial port forever in this case. It stops reading if the serial interface is given a time-out. There are two possibilities:

use readStringUntil() on the receiver
call mySerial.setTimeout(300); (from setup()) to set a 300ms (for instance, as long as it's significantly less than 1000) time out on the receiver — it defaults to one second!

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