SoftwareSerial example not working as expected

Question

I recently bought an Arduino UNO to read the data outputted by my Smart Meter. The meter uses serial communication and I would like to see the values being outputted on my laptop screen. I figured I would need to use the SoftwareSerial library to read the incoming data and print that data on my screen using the hardware serial and the Serial Monitor in the Arduino IDE. To become familiar with (software) serial communication on the Arduino, I reviewed the documentation of the SoftwareSerial library. Problem is, I can't get the most basic example to work and I have been stuck on this for quite a while now. The example code is below, the example can be found here

#include <SoftwareSerial.h>

SoftwareSerial mySerial(10, 11); // RX, TX

void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(57600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }


  Serial.println("Goodnight moon!");

  // set the data rate for the SoftwareSerial port
  mySerial.begin(4800);
  mySerial.println("Hello, world?");
}

void loop() { // run over and over
  if (mySerial.available()) {
    Serial.write(mySerial.read());
  }
  if (Serial.available()) {
    mySerial.write(Serial.read());
  }
}

As far as I understand this, the following should happen: - Type text in Serial Monitor window. - Serial.read() reads this data and writes it to the Software Serial. - The Software Serial reads this data and writes it back to Serial. - That which was written appears on the screen.

But whatever I try, nothing happens. Among things I tried to following: - Change the baud rate for both software and hardware serial (9600 for instance). - Tried a different SoftwareSerial library (AltSoftSerial). - Tried different RX and TX pins for SoftwareSerial. - Instead of Serial.write(mySerial.read());, store the result in a char first.

I'm probably missing something obvious. I would be grateful to anyone who could shed some light on this or offer an alternative way for me to read the data from my Smart Meter.

Edit

I had no wiring, because the example specified "There is no circuit for this example". I tried all three options suggested by @slash-dev, but none had the expected behaviour:

SoftwareSerial with wires connecting pin 1 to pin 10 and pin 0 to pin 11. It prints strange characters:

Goodnight moon!
Ùniÿhtÿmoÿn!ÿ
nihtmoÿttt

AltSoftSerial with wires connecting 1-8 and 0-9. First prints Goodnight moon! and then it keeps printing Ôë‹¹¥�¡Ñ�moon!.

NeoSWSerial with wires connecting 1-10 and 0-11. Same as AltSoftSerial but keeps printing Ôë‹–+ë¡Ñ�j½½¹…j.

The Iskra 382, manual can be [found here](http://iskrame382.com/iskra_me382_-_manual.pdf). I want to gather information about the energy usage and store this data in a database on my own server. — Erwin Janssen, Nov 11 '16 at 18:26
Have you connected ground on the Arduino UNO to ground of the smart meter? This is the kind of behaviour you might see if you forget that :) — J. P. Petersen, Nov 11 '16 at 18:27

slash-dev · Answer 1 · 2016-11-11T20:46:06.033

The baud rates must be the same on Serial and mySerial.

And you don't describe the connections, so I have to ask: Did you connect a wire from pin 1 (Serial transmit) to pin 10 (mySerial receive), and another wire from pin 0 (Serial receive) to pin 11 (mySerial transmit)? Note how they are crossed.

AltSoftSerial is really the best choice, but it only works on pin 8 (RX) and pin 9 (TX), which would require connecting 8 to 1 and 9 to 0. SoftwareSerial is very inefficient, because it disables interrupts for long periods of time. This can interfere with other parts of your sketch or other libraries.

My NeoSWSerial library is another alternative. It's almost as efficient as AltSoftSerial, but it works on any two pins. It can transmit and receive at the same time (unlike SoftwareSerial), but it only works at bauds 9600, 19200 and 38400.

EDIT:

I think what you've tried is probably working ok. All the software serial libraries use interrupts for processing individual bits instead of one interrupt per character. When there are other interrupts in the system (millis() TIMER0 or Serial), the bit "calculations" can be affected. This manifests as receiving the wrong byte. Your loopback test makes it especially susceptible because the sending and receiving are synchronized (the initial receive interrupt occurs while the transmit interrupt is starting the next char).

If you just hook 0 to 1, I think it will work, because the UART is able to send and receive at the same time, and it deals with complete characters, not bits. The character interrupts do not disturb the sending or receiving of the bits.

In developing the NeoSWSerial library, I have seen this manifest the same way. I had to use two Arduinos to fully test asynchronously (i.e., not synchronized). In your case, using AltSoftSerial for the SmartMeter should work fine, and you can choose different baud rates. If you are echoing the SmartMeter characters to Serial, be sure you have a higher baud rate on Serial.

score 0 · Answer 2 · answered Apr 06 '22 at 19:18

0

This is most likely not related to the issues now 5 years ago, but in my case I was using the Arduino IDE 2.0.0-rc5 which was not writing to the soft serial for unknown reasons. I downgraded to Arduino IDE 1.8.19 and the same serial sketch worked.

answered Apr 06 '22 at 19:18

k_o_

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SoftwareSerial example not working as expected

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