Using only TX of SoftwareSerial, leaving RX pin free

[tobek]

Hi everyone.

I'm using SparkFun's OpenLog, a microSD card data-logger to which you communicate through serial. The only connection needed is Arduino TX to OpenLog RX, because the OpenLog handles the rest.

I have run out of pins in the project I'm using, and have exactly one digital I/O pin left to use for the OpenLog. I'm using SoftwareSerial. However, when I declare an instance of SoftwareSerial, I need to give it 2 pins: RX and TX. I only need TX, and every other pin on my Arduino (Nano) is currently being used for output.

Will something go wrong if I declare SoftwareSerial with an RX pin that's actually being used elsewhere for output? Can I, instead, declare SoftwareSerial with a pin that doesn't exist - say, 100? Any other options?

Thanks for any advice!

[nickgammon]

I wouldn't use pin 100 or anything like that, because it tries to use that pin, eg. here:

Code: [Select]

void SoftwareSerial::setRX(uint8_t rx)
{
  pinMode(rx, INPUT);
  if (!_inverse_logic)
    digitalWrite(rx, HIGH);  // pullup for normal logic!
  _receivePin = rx;
  _receiveBitMask = digitalPinToBitMask(rx);
  uint8_t port = digitalPinToPort(rx);
  _receivePortRegister = portInputRegister(port);
}


They don't seem to have allowed for no Rx at all, so you might be better off taking the class, and making a "send-only" version by removing the references to the reading part. I'll take a stab at it, shouldn't take long.

[nickgammon]

I adapted SoftwareSerial to only have a send function. Download library here:

http://gammon.com.au/Arduino/SendOnlySoftwareSerial.zip

Example of use:

Code: [Select]

#include <SendOnlySoftwareSerial.h>

SendOnlySoftwareSerial mySerial (3);  // Tx pin

void setup ()
  {
  mySerial.begin(115200);
  }

int i;

void loop ()
{
  mySerial.print ("test: ");
  mySerial.println (i++);
  delay (100);
}

[tobek]

Thanks so much, that's brilliant, I appreciate it!

[glenndrives]

Fantastic! Thank you very much.

Glenndrives

[MushfiqSarker]

You can set RX to 0.

Code: [Select]

SoftwareSerial Serial2 = SoftwareSerial(0, 4);    //!< RX is 0. Pin 4 is TX

This works because there is no pin 0.

Mushfiq

[nickgammon]

Yes there is a pin 0. Take a look at your board. It's labelled Rx (and 0).

[maeterlinck]

Thanks Nick!

Just what I was looking for. 

[meman]

I adapted SoftwareSerial to only have a send function. Download library here:

http://gammon.com.au/Arduino/SendOnlySoftwareSerial.zip

Example of use:

Code: [Select]

#include <SendOnlySoftwareSerial.h>

SendOnlySoftwareSerial mySerial (3);  // Tx pin

void setup ()
  {
  mySerial.begin(115200);
  }

int i;

void loop ()
{
  mySerial.print ("test: ");
  mySerial.println (i++);
  delay (100);
}

in my case I want to release TX pin
how I can change the library in order to implement this method?
more info:
http://forum.arduino.cc/index.php?topic=227760.0

[nickgammon]

I adapted SoftwareSerial to only have a receive function. Download library here:

http://gammon.com.au/Arduino/ReceiveOnlySoftwareSerial.zip

Example of use:

Code: [Select]


#include <ReceiveOnlySoftwareSerial.h>

ReceiveOnlySoftwareSerial mySerial(10); // RX

void setup() 
{
  Serial.begin(115200);
  while (!Serial) { }  // wait for Serial to become available

  // set the data rate for the ReceiveOnlySoftwareSerial port
  mySerial.begin(9600);
}

void loop() // run over and over
{
  // echo from software serial to hardware serial
  if (mySerial.available())
    Serial.write(mySerial.read());
}


This could be handy for situations (like reading from a GPS) where you don't need to write, and thus you can save a few hundred bytes of program code.

[yair]

had to add a line in your send only cpp file to make it work with micronuclius/digispark cores running at 16.5MHz.
see http://digistump.com/board/index.php/topic,212.msg1214/topicseen.html#msg1214

thank you nick, again

[orthho]

I adapted SoftwareSerial to only have a receive function. Download library here:

http://gammon.com.au/Arduino/ReceiveOnlySoftwareSerial.zip

Example of use:

Code: [Select]


#include <ReceiveOnlySoftwareSerial.h>

ReceiveOnlySoftwareSerial mySerial(10); // RX

void setup() 
{
  Serial.begin(115200);
  while (!Serial) { }  // wait for Serial to become available

  // set the data rate for the ReceiveOnlySoftwareSerial port
  mySerial.begin(9600);
}

void loop() // run over and over
{
  // echo from software serial to hardware serial
  if (mySerial.available())
    Serial.write(mySerial.read());
}


This could be handy for situations (like reading from a GPS) where you don't need to write, and thus you can save a few hundred bytes of program code.

Hi Nick !

I want to ask question,
I'm using Arduino UNO, and i want to reduce I/O pin..
Is it possible to combine your library and SoftwareSerial library?
because when i tried your library alone thats perfect !

right now i try to combine your library to SoftwareSerial in order to retrieve data serial from my ID-12 (RFID) and send it to other device using Serial too..



this is my code

Code: [Select]

#include <SoftwareSerial.h>
#include <ReceiveOnlySoftwareSerial.h>

// DEFINE
// ======== SERIAL =============
// == RFID
#define RXID  8
ReceiveOnlySoftwareSerial RFID (RXID);

// == RS 485
#define RX45           2
#define TX45           3
#define SerialControl  7
#define Transmit       HIGH
#define Receive        LOW
SoftwareSerial toSlave (RX45, TX45);

void setup(){
}

void loop(){
}

and these the error message

Code: [Select]

This report would have more information with
  "Show verbose output during compilation"
  enabled in File > Preferences.
Arduino: 1.0.6 (Windows 7), Board: "Arduino Uno"
ReceiveOnlySoftwareSerial\ReceiveOnlySoftwareSerial.cpp.o: In function `__vector_3':
--------------\Arduino\libraries\ReceiveOnlySoftwareSerial/ReceiveOnlySoftwareSerial.cpp:300: multiple definition of `__vector_3'
SoftwareSerial\SoftwareSerial.cpp.o:--------.cpp:305: first defined here
ReceiveOnlySoftwareSerial\ReceiveOnlySoftwareSerial.cpp.o: In function `__vector_4':
---------------\Arduino\libraries\ReceiveOnlySoftwareSerial/ReceiveOnlySoftwareSerial.cpp:307: multiple definition of `__vector_4'
SoftwareSerial\SoftwareSerial.cpp.o:-------\Arduino\libraries\SoftwareSerial/SoftwareSerial.cpp:312: first defined here
ReceiveOnlySoftwareSerial\ReceiveOnlySoftwareSerial.cpp.o: In function `__vector_5':
---------------\Arduino\libraries\ReceiveOnlySoftwareSerial/ReceiveOnlySoftwareSerial.cpp:314: multiple definition of `__vector_5'
SoftwareSerial\SoftwareSerial.cpp.o:-------------\Arduino\libraries\SoftwareSerial/SoftwareSerial.cpp:319: first defined here

Thanks ~

[nickgammon]

Once you have SoftwareSerial you can have multiple instances of it (I think), so you don't need to combine the libraries.

[orthho]

Hi Nick ! Thanks for your reply

Ya you were right, SoftwareSerial can allow us to have Serial Port programming more than 1..I've tried it with two Serial port. And it works.. But I haven't tried it for more than two yet.
Ah.. ok.. I understand.. I just tried to minimize my I/O pin so I try to combine it with your library.

Thanks Nick ~

[nickgammon]

Quite possibly the pin you chose. Please post your code. Also state which Arduino you have.

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