read payload only (NFC tag emulation)

Projects Programming
1

hi everyone,

iam using the seedstudio v2 nfc board and i only want to select the payload of what i send trough nfc to arduino to show up on the serial monitor. (Tag emulation)

this is my code:

#include "SPI.h"
#include "PN532_SPI.h"
#include "emulatetag.h"
#include "NdefMessage.h"

PN532_SPI pn532spi(SPI, 10);
EmulateTag nfc(pn532spi);
uint8_t ndefBuf[120];
//////////////////////////////
const int led = 13;
String content = "";
char character;
void setup()
{
  Serial.begin(9600);
  Serial.println("------- Emulate Tag --------");
  pinMode(led, OUTPUT);

  nfc.init();
}

void loop(){
  // start emulation (blocks)
  nfc.emulate();

  if(nfc.writeOccured()){
    digitalWrite(led, HIGH);
    Serial.println("\nWrite occured !");
    uint8_t* tag_buf;
    uint16_t length;

    nfc.getContent(&tag_buf, &length); 
    NdefMessage msg = NdefMessage(tag_buf, length);
    msg.print();
  }
  delay(1000);
}

currently i get this is my serial monitor:

////////////////////////////////////////////////////

Write occured !

NDEF Message 1 record, 16 bytes
NDEF Record
TNF 0x1 Well Known
Type Length 0x1 1
Payload Length 0xC 12
Type 54 T
Payload 02 65 6E 6F 6E 6C 79 20 74 68 69 73 .only this <-- thats the only thing i want to show in the serial monitor
Record is 16 bytes

////////////////////////////////////////////////////////

things i tried to select the payload: indexof(), msg.substring() and tried this (stackoverflow)

i hope you guys can help me out a bit, would really appreciate it :slight_smile:

2

Links to the libraries you are using would be good.

3

testmaniac:
hi everyone,

iam using the seedstudio v2 nfc board and i only want to select the payload of what i send trough nfc to arduino to show up on the serial monitor. (Tag emulation)

::::SNIP::::

things i tried to select the payload: indexof(), msg.substring() and tried this (stackoverflow)

i hope you guys can help me out a bit, would really appreciate it :slight_smile:

The easiest way is to change it to a String object.

References:

This should work. If it does not, I'll be happy to help.

Change from:

 NdefMessage msg = NdefMessage(tag_buf, length);
 msg.print();

to:

 String msg = NdefMessage(tag_buf, length);
 indx = msg.indexOf('Payload');
 if (indx != -1) {
     payload = msg.substring(indx)
     Serial.println(payload);
 }
4

It's work ??? Because me not work..

when i change

"NdefMessage msg = NdefMessage(tag_buf, length);
msg.print(); "

to

" String msg = NdefMessage(tag_buf, length);
indx = msg.indexOf('Payload');
if (indx != -1) {
payload = msg.substring(indx)
Serial.println(payload);
}"

there is a problem :

C:\Users\Thierry\Desktop\emulation\emulation.ino:34:21: warning: character constant too long for its type [enabled by default]

indx = msg.indexOf('Payload');

^

C:\Users\Thierry\Desktop\emulation\emulation.ino: In function 'void loop()':

emulation:33: error: conversion from 'NdefMessage' to non-scalar type 'String' requested

String msg = NdefMessage(tag_buf, length);

^

emulation:34: error: 'indx' was not declared in this scope

indx = msg.indexOf('Payload');

^

C:\Users\Thierry\Desktop\emulation\emulation.ino:34:30: warning: overflow in implicit constant conversion [-Woverflow]

indx = msg.indexOf('Payload');

^

emulation:36: error: 'payload' was not declared in this scope

payload = msg.substring(indx)

^

emulation:37: error: expected ';' before 'Serial'

Serial.println(payload);

^

exit status 1
conversion from 'NdefMessage' to non-scalar type 'String' requested

5

do u have an answer ? Can u read the only payload ?

6

do u have an answer ?

Do not do things that do not make sense. You can NOT assign an instance of NdefMessage to a String.

YOU must look at the NdefMessage class and figure out how to print (or save) just the portion you want.