Esp32-snippets: setValue() argument as a string or a uint16

[Tavo7995]

Hey so Ive been trying to use the ble uart example to send continuous sensor data to an android app, and I can send uint8 but I wanted to send uint16 so as to make decimal places and make the reading more accurate. I have tried setting the number as a string but it only accepts it if is within double quotations.
so it will take pCharacteristic->setValue("sensorValue");
but not pCharacteristic->setValue(sensorValue); (sensorValue having been converted into a string earlier)
Is there something I am missing or some way around this?
I am using the Arduino IDE.
Thanks!

[nkolban]

The value for a characteristic is a "sequence of bytes". These bytes (data) are then stored by the BLE Server and made available to a BLE client that requests them. What the bytes represent is a private contract between the BLE Server and the BLE client. The API exposed through these BLE classes allows you to set the value of a characteristic. You can set the value to a sequence of bytes.

In C++, there is no "Buffer" data type for holding arbitrary sequences of bytes ... however, convention holds that we use the std::string data type. This is the C++ standard data type that holds strings. However, any sequence of bytes can be stored in a string. When we create a std::string instance, we code the following:

std::string myString(pointerToData, lengthOfData);

To have a unit16_t stored in the string we would thus code:

std::string myStringForUnit16((char*)&myUint16, 2);

we could then set the characteristic by pasing that string:

pCharacteristic->setValue(myStringForUnit16);

I'd suggest also grabbing a big cup of coffee and having a read of the std::string data type which you can find by googling.

[nkolban]

Closing for just now. Don't hesitate to re-open as needed.

[Girish1389]

Hi this is my first post on BLE issue which i am facing.
Kindly help me out.
I am using the ble write example to read sensor data to an android app, whenever i am writing prefered string"sensor data". I am not able to read the sensor data, when i am calling the function return value in the code. kindly help me to solve the issue which i am facing.
Thanking you.
if i take pCharacteristic->setValue("sensorValue")
only able to read the sting not the sensor value in the app.

[chegewara]

You dont have to set value as string:
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/BLECharacteristic.h#L76-L82
unless you are working with arduino-ide then it may be not added yet, then just copy/paste BLECharacteristic.cpp and .h files into your library.

[Girish1389]

Sir I am trying to read the sensor data, by calling the function return value but, I am not able to read the LDR sensor value into my android app.
if (value=="LDR value")
{
pCharacteristic->setValue(LDR());
LDR();
error: no matching function for call to 'BLECharacteristic::setValue(float)'
pCharacteristic->setValue(LDR())
kindly suggest me.

[chegewara]

Wait until repository will be updated or like i said earlier copy/paste code from those 2 files:

https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/BLECharacteristic.h
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/BLECharacteristic.cpp

In my case those 2 files are in folder:
C:\Users\admin\Documents\Arduino\hardware\espressif\esp32\libraries\BLE\src
but you may have it also in this folder:
C:\Users\admin\Documents\Arduino\libraries\ESP32BLE_library
or something like that.

[Girish1389]

Sir I have added the above mentioned BLECharacteristic.h and BLECharacteristic.cpp into my source code folder.
I am attaching my code below.

include

include

include

include

include

include

define GAP_UUID "6f3273a0-f831-4b0f-b609-2477208f8c2b"

define GATT_UUID "0c401a07-3fef-4a77-9efc-36458a21c7ba"

define SERVICE_UUID GAP_UUID

define CHARACTERISTIC_UUID GATT_UUID

int sensorPin = 34; // select the input pin for ldr
int sensorValue = 0;
float LDR(void)
{
float luminosity;
sensorValue = analogRead(sensorPin); // read the value from the sensor
luminosity = (3.3sensorValue)/4095;
return (luminosity);
}
class MyCallbacks: public BLECharacteristicCallbacks
{
void onWrite(BLECharacteristic *pCharacteristic)
{
std::string value = pCharacteristic->getValue();
if (value.length() > 0)
{
//Serial.println("**");
//Serial.print("New value: ");
for (int i = 0; i < value.length(); i++)
Serial.print(value[i]);
Serial.println();
}
if (value=="LDR value")
{
pCharacteristic->setValue("LDR()");
LDR();
Serial.println(LDR());
}
}
}
};
void setup() {
Serial.begin(115200);
BLEDevice::init("test");
BLEServer *pServer = BLEDevice::createServer();

BLEService *pService = pServer->createService(SERVICE_UUID);

BLECharacteristic *pCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID,
BLECharacteristic::PROPERTY_READ |
BLECharacteristic::PROPERTY_WRITE
);
pCharacteristic->setCallbacks(new MyCallbacks());
pService->start();

BLEAdvertising *pAdvertising = pServer->getAdvertising();
pAdvertising->start();
pinMode(led,OUTPUT); pinMode(sensorPin,INPUT);
LDR();
}
void loop()
{
// put your main code here, to run repeatedly:
delay(2000);
}

I am only able to read in my serial monitor but not in my app.