Message received with 1 character less

Question

I have the following situation:

One Arduino Uno with a 433mhz transmitter wired to the laptop to have serial communication. Another Arduino Uno with a 9V battery wired with a 433mhz receiver and an LCD screen (16x2, I2C).

I have the following code to transmit:

#include <VirtualWire.h>
void setup() {
 //Force low when enabled
 vw_set_ptt_inverted(true);
 //Set pin 12 for transmitter
 vw_set_tx_pin(12);
 //Setup with speed of the data transfer.
 vw_setup(4000);
 //Set serial communication at 9600 baud
 Serial.begin(9600);//set Serial
 //Set pin 13 to light up when transmitting
 pinMode(13,OUTPUT);
}
void loop() {
 //If message send via serial monitor
 if (Serial.available()) {
 //wait a bit for the entire message to arrive
 delay(100);
 while (Serial.available() > 0) {
 //Read serial into string
 String message = Serial.readString();
 //Initialize char array
 char msg[message.length()];
 //Write string to char array
 message.toCharArray(msg, message.length());
 //send char array as unsigned int (bits)
 vw_send((uint8_t *)msg, strlen(msg));
 //Wait until the complete message has been send
 vw_wait_tx();
 //Turn on light when finished
 digitalWrite(13,HIGH);
 delay(200);
 }
 }else{
 //Turn off light
 digitalWrite(13, LOW); 
 }
}

And the following code to receive a message and print on a LCD screen:

#include <LiquidCrystal_I2C.h>
#include <VirtualWire.h>
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Set the LCD I2C address
void setup() {
 //start up LCD with 16 chars with 2 lines
 lcd.begin(16,2); 
 //Turn on backlight
 lcd.backlight();
 //Write initialising message
 lcd.setCursor(0,0);
 lcd.print("Initialisation..");
 //Force low when enabled
 vw_set_ptt_inverted(true); 
 //Set pin 12 to receive
 vw_set_rx_pin(12);
 //Setup with speed of the data transfer.
 vw_setup(4000);
 //set pin 13 for light
 pinMode(13, OUTPUT);
 //Start receiver
 vw_rx_start(); 
 //Set message on LCD that setup has completed
 lcd.setCursor(0,1); 
 lcd.print("Completed!");
}
void loop() {
 //initialize array for message
 uint8_t msg[VW_MAX_MESSAGE_LEN];
 uint8_t msgLength = VW_MAX_MESSAGE_LEN;
 //If message received
 if (vw_get_message(msg, &msgLength)){
 //Turn on light
 digitalWrite(13, HIGH);
 //Print on lcd
 lcd.clear();
 lcd.setCursor(0,0);
 lcd.write(msg, msgLength);
 }else{
 //Else turn of light
 digitalWrite(13, LOW);
 }
}

My problem is that the message that is being transmitted and received by the other arduino always is short 1 character. For example if I send "test", it receives and displays "tes". What am I missing?

(My short solution was to just add a space to the message, then the space got cut off. But I want to understand what is going wrong.)

• Majenko: One thing that immediately jumps out at me is your flawed serial methodology. You should read this: hacking.majenko.co.uk/reading-serial-on-the-arduino

Answer 1

I haven't found the source of the problem by reading through the code, and will limit my comments to advice about debugging the problem.

With the code as it stands, there are half a dozen points where the missing character might have dropped out. With just a final result, the problem location is difficult to narrow down. Modify your code to display intermediate data.

For example, in the sending code, print the read-in string and its length to Serial. Eg, if you #include <Streaming.h> you can say:

Serial << message << ' ' << message.length() << endl; Serial << msg << ' ' << strlen(msg) << endl;

and so forth.

[Note, msg actually occupies strlen(msg)+1 bytes, the last byte being a null-byte terminator, which your code doesn't send or receive.]

In the receiving code, besides the lcd.write of msg, do an lcd.print with msgLength.

You can also do some code clean-up in the sender. Remove the line

while (Serial.available() > 0) {, and its corresponding }, because Serial.readString() already contains a character-wait loop with timeout.

• Revils: Thank you for the tips. Im not that familiar with serial/arduino, just started. So these comments about the code are nice!