BLETypeCharacteristic Byte characteristic

[pabloglc]

Hi all,

I'm using the library BLEPeripheral.h and an nRF52-DK for sending data from sensors to an app.
I want to send the data by byte packages. I manage to do it with 4 bytes as the characteristic type is set as INT.
The problem is if I want to send more bytes (as int has only 4 bytes).
My code (not all):

#define bytes_to_u32(a,b,c,d) (((unsigned int) ((unsigned char) a)) & 255)<<24 | (((unsigned char) b)&255)<<16 | (((unsigned char) c)&255) <<8 | (((unsigned char) d)&255) 

BLEService wifiIP_service = BLEService("faa0");
BLEUnsignedIntCharacteristic wifiIP1_Char("faa1", BLERead  | BLENotify | BLEWrite);
BLEDescriptor wifiIP1_Descriptor = BLEDescriptor("2901", "IP");

and the function for this:

byte dataArray[4];
void WIFI(){
// RECEIVE IP ADDRESS
  Wire.requestFrom(106, 4);    // request 6 bytes from slave device #8
  
  while (Wire.available()) {

    for(int i=0; i<4; i++){
       dataArray[i] = Wire.read();
    }

  uint32_t ip = bytes_to_u32(dataArray[0],dataArray[1],dataArray[2],dataArray[3]);

  wifiIP1_Char.setValue(ip);

    delay(500);
  }
}

In this example it works because I have only 4 values, but I have other characteristics with 6 values.

[J-M-L]

instead of using a BLEUnsignedIntCharacteristic which sets the size to an unsigned int as you noticed, you should create your own characteristic for the service using

BLECharacteristic(uuid, properties, value, valueSize); // https://www.arduino.cc/reference/en/libraries/arduinoble/blecharacteristic/

(the value is seen as a string)

[pabloglc]

I'm trying but I don't know how to declare it.
What would be the equivalent to BLEUnsignedLongCharacteristic wifiIP1_Char("faa1", BLERead | BLENotify | BLEWrite);?
Any example?

[J-M-L]

Sorry I just (stupidly) copied/paste the doc and it is wrong, you don't pass the value at that time, only its size

This is documented in the code for the constructor

  BLECharacteristic(const char* uuid, uint8_t properties, int valueSize, bool fixedLength = false);

So for your case that would be

BLECharacteristic wifiIP1_Char("faa1", BLERead | BLENotify | BLEWrite, 6, true); // 6 bytes, fixed length

---

if you read the code, you'll see they actually use those parameters to instantiate a BLELocalCharacteristic

BLECharacteristic::BLECharacteristic(const char* uuid, uint8_t properties, int valueSize, bool fixedLength) :
  BLECharacteristic(new BLELocalCharacteristic(uuid, properties, valueSize, fixedLength))
{}

and this is where the memory buffer is dynamically allocated on the heap, matching the size of your valueSize

  _value = (uint8_t*)malloc(valueSize);

When you ask for the value, you get a pointer (uint8_t* ) to that buffer. (see ArduinoBLE/BLECharacteristic.cpp at 4c149a206c3e36c909cbb6a9c6032940fc806a88 · arduino-libraries/ArduinoBLE · GitHub)

[pabloglc]

The problem is that this is the library ArduinoBLE which is a bit different from BLEPeripheral, I tried to use ArduinoBLE with no luck.

[J-M-L]

do you have a link to that library?

[pabloglc]

GitHub - sandeepmistry/arduino-BLEPeripheral at 0.4.0

Maybe I just need to check for another library or another way to do this.

[J-M-L]

it seems very close to the other one.

have you tried

BLECharacteristic wifiIP1_Char("faa1", BLERead | BLENotify | BLEWrite, 6, true); // 6 bytes, fixed length

does it compile?

[pabloglc]

I tried but I have these errors:

no instance of constructor "BLECharacteristic::BLECharacteristic" matches the argument list`
no matching function for call to 'BLECharacteristic::BLECharacteristic(const char [5], int, int, bool)'

And then if I try to set the value with: wifiIP1_Char.setValue(ip); I have:

no instance of overloaded function "BLECharacteristic::setValue" matches the argument list

[J-M-L]

drop the true at the end

BLECharacteristic wifiIP1_Char("faa1", BLERead | BLENotify | BLEWrite, 6);

for the second one you want to pass an array and the size

unsigned char ip[6] =  "HELLO"; // for testing purpose
wifiIP1_Char.setValue(ip, 6);

[pabloglc]

It works! With some changes. In my case it would be:

BLECharacteristic wifiIP1_Char("faa1", BLERead | BLENotify | BLEWrite, 4);

char IP[4] ={dataArray[0],dataArray[1],dataArray[2],dataArray[3]};
wifiIP1_Char.setValue(IP);

Not sure if I can use unsigned char, but I don't really need it.
Thank you!

[J-M-L]

Glad you got it to work

(the function setValue expects unsigned char so you should provide this for type coherence and an IP only has numbers between 0 and 255 so you don't want a signed char - which some compilers could give you)