How to use variables in ST25DV NFC message?

Projects Programming
1

HI
I am trying to do a (probably) simple project, well I thought.
All I want to do is send a variable value from a poti ( on A0) to the ST25DV NFC message.
however I cant get the analogread value transformed to anything the message will accept..
The ST25DV is connected to a Adafruit QT PY Stemma. with the stemma QT cable.

I tried to modifiy the simple example: but fails..
whats wrong?
thanks



#include "ST25DVSensor.h"

#define SerialPort Serial

#if defined(ARDUINO_B_L4S5I_IOT01A)
// Pin definitions for board B-L4S5I_IOT01A
#define GPO_PIN PE4
#define LPD_PIN PE2
#define SDA_PIN PB11
#define SCL_PIN PB10
#define WireNFC MyWire
TwoWire MyWire(SDA_PIN, SCL_PIN);
ST25DV st25dv(12, -1, &MyWire);
#else
#define DEV_I2C Wire
ST25DV st25dv(12, -1, &DEV_I2C);
#endif

void setup() {
const char uri_write_message[] = "st.com/st25"; // Uri message to write in the tag
const char uri_write_protocol[] = URI_ID_0x01_STRING; // Uri protocol to write in the tag
String uri_write = String(uri_write_protocol) + String(uri_write_message);

// Initialize serial for output.
SerialPort.begin(9600);

// The wire instance used can be omitted in case you use default Wire instance
if(st25dv.begin() == 0) {
SerialPort.println("System Init done!");
} else {
SerialPort.println("System Init failed!");
while(1);
}

if(st25dv.writeURI(uri_write_protocol, uri_write_message, "")) {
SerialPort.println("Write failed!");
while(1);
}

}

void loop() {
int sensorValue = analogRead(A0);
Serial.println(sensorValue);


char cstr[10];
itoa(sensorValue, cstr, 10);


char uri_write_message[] = {cstr}; // Uri message to write in the tag
const char uri_write_protocol[] = URI_ID_0x01_STRING; // Uri protocol to write in the tag
String uri_write = String(uri_write_protocol) + String(uri_write_message);

if(st25dv.writeURI(uri_write_protocol, uri_write_message, "")) {
SerialPort.println("Write failed!");
while(1);
}

delay(1000);
}
2

How, exactly, does it "fail" ?

Have you got the unmodified example working?

3

It will not accept the modified variable in the loop: uri_write_message

here the original unmodified example:


#include "ST25DVSensor.h"

#define SerialPort      Serial

#if defined(ARDUINO_B_L4S5I_IOT01A)
// Pin definitions for board B-L4S5I_IOT01A
  #define GPO_PIN PE4
  #define LPD_PIN PE2
  #define SDA_PIN PB11
  #define SCL_PIN PB10
  #define WireNFC MyWire
  TwoWire MyWire(SDA_PIN, SCL_PIN);
  ST25DV st25dv(12, -1, &MyWire);
#else
  #define DEV_I2C         Wire
  ST25DV st25dv(12, -1, &DEV_I2C);
#endif

void setup() {
  const char uri_write_message[] = "st.com/st25";       // Uri message to write in the tag
  const char uri_write_protocol[] = URI_ID_0x01_STRING; // Uri protocol to write in the tag
  String uri_write = String(uri_write_protocol) + String(uri_write_message);

  // Initialize serial for output.
  SerialPort.begin(115200);

  // The wire instance used can be omitted in case you use default Wire instance
  if(st25dv.begin() == 0) {
    SerialPort.println("System Init done!");
  } else {
    SerialPort.println("System Init failed!");
    while(1);
  }

  if(st25dv.writeURI(uri_write_protocol, uri_write_message, "")) {
    SerialPort.println("Write failed!");
    while(1);
  }

}

void loop() {  
  //empty loop
}
4

What do you mean by that? Do you get a compiler error? A runtime error? Or what?

5

here the errors :
auge.ino: In function 'void loop()':
auge.ino:53:31: error: invalid conversion from 'char*' to 'char' [-fpermissive]
53 | char uri_write_message[] = {cstr}; // Uri message to write in the tag
| ^~~~
| |
| char*

exit status 1

Compilation error: invalid conversion from 'char*' to 'char' [-fpermissive]

6

You need to post the message using the <CODE/> button - then the little arrow would line-up to point at the error it's referring to.

But the problem is:

auge.ino:53:31: error: invalid conversion from 'char*' to 'char'

ie, it wants something of type char, but you given it something of type char* - ie, a pointer to a char.

Not quite sure what you're intending here;

char cstr[10];
itoa(sensorValue, cstr, 10);

char uri_write_message[] = {cstr};

The itoa loads your sensor value as a string into the char array cstr - so why not just use that directly?

String uri_write = String(uri_write_protocol) + String(cstr);

I you wanted to copy the contents of cstr into another array, you would need to use strcpy or similar.

7

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