Passing Uptime Value through BLE to Android

Using Arduino Programming Questions
1

Good afternoon everyone,

Just been experimenting with the Uptime in serial, a nice little library that will save me some time using for-loops.

I'm trying to use the uptime library with BLE, and pass through to n rfConnect on Android the value of the uptime, updating every 1000ms via delay.

My code compiles, but the android value stays at (0x) 00-00-00-00, what am I missing here? I've put comments in the code below.

#include <uptime.h>
#include <uptime_formatter.h>

#include <BLEDevice.h>
#include <BLEUtils.h>
#include <BLEServer.h>

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"

//global variable
int uptime = uptime::getSeconds();



class MyCallbacks: public BLECharacteristicCallbacks {
    void onRead(BLECharacteristic *pCharacteristic) {
      std::string value = pCharacteristic->getValue();
 }

};

void setup() {
  Serial.begin(115200);
  BLEDevice::init("MyESP32");
  BLEServer *pServer = BLEDevice::createServer();
  BLEService *pService = pServer->createService(SERVICE_UUID);

  BLECharacteristic *pCharacteristic = pService->createCharacteristic(
                                         CHARACTERISTIC_UUID,
                                         BLECharacteristic::PROPERTY_READ
                                       );

  pCharacteristic->setCallbacks(new MyCallbacks());
  pCharacteristic->setValue(uptime); ////EXPECTED BEHAVIOR: update every second on android device as a int, RESULT: value stayed at (0x) 00-00-00-00
    
    pService->start();

    BLEAdvertising *pAdvertising = pServer->getAdvertising();
    pAdvertising->start();


}

void loop() {
 //update the second every 1000ms
  uptime::getSeconds();
  delay(1000);
 }

TIA, Sam

2

This statement in loop() only gets and throws away the current uptime:

3

The variables: pServer, pService and pCharacteristic should be global variables. In loop() you must call pCharacteristic->setValue(std::to_string(uptime::getSeconds())); and that should be the end of that.

EDIT: convert long to string, if the string version of setValue() is to be used.

4

This is returning an unsigned long. You may want to define the characterisitic for that type, or possibly you can use this to send the 4 bytes.

pCharacteristic->setValue((uint8_t*)&uptime::getSeconds(),4);

5

That's probably not gonna work, but this may:

unsigned long uptime;

setup()
{
  pCharacteristic->setValue((uint8_t*)&uptime, sizeof(uptime));
}

loop()
{
  uptime = uptime::getSeconds();
}
6

I've tried giving the solution above an attempt, the code compiles but there is no output. Do BLE Characteristics have default declaration types as global variables? Updated code below:

#include <uptime.h>
#include <uptime_formatter.h>

#include <BLEDevice.h>
#include <BLEUtils.h>
#include <BLEServer.h>

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"

//global variable
unsigned long uptime;




class MyCallbacks: public BLECharacteristicCallbacks {
    void onRead(BLECharacteristic *pCharacteristic) {
      std::string value = pCharacteristic->getValue();
 }

};

void setup() {
  Serial.begin(115200);
  BLEDevice::init("MyESP32");
  BLEServer *pServer = BLEDevice::createServer();
  BLEService *pService = pServer->createService(SERVICE_UUID);

  BLECharacteristic *pCharacteristic = pService->createCharacteristic(
                                         CHARACTERISTIC_UUID,
                                         BLECharacteristic::PROPERTY_READ
                                       );

  pCharacteristic->setCallbacks(new MyCallbacks());
  pCharacteristic->setValue((uint8_t*)&uptime, sizeof(uptime));
    
    pService->start();

    BLEAdvertising *pAdvertising = pServer->getAdvertising();
    pAdvertising->start();


}

void loop() {
 //update the second every 1000ms
   uptime = uptime::getSeconds();
  delay(1000);
 }
7

You are setting the value as a binary value and reading it out as a string. Set the value as a string (in loop) as described in #3 OR change this part of the code:

void onRead(BLECharacteristic *pCharacteristic) {
  //std::string value = pCharacteristic->getValue(); //Old
  pCharacteristic->setValue(std::to_string(uptime)); //New
 }
8

As said before, you need to write the new values in loop()

void loop() {
 //update the second every 1000ms
   uptime = uptime::getSeconds();
   pCharacteristic->setValue((uint8_t*)&uptime, sizeof(uptime));
  delay(1000);
 }

nrfConnect will show the four hex bytes being sent.

9

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