Write the value of the characteristic. If the characteristic is on a remote device, a write request or command will be sent.
bleCharacteristic.writeValue(buffer, length)
bleCharacteristic.writeValue(value)
// read the button pin
int buttonState = digitalRead(buttonPin);
if (oldButtonState != buttonState) {
// button changed
oldButtonState = buttonState;
if (buttonState) {
Serial.println("button pressed");
// button is pressed, write 0x01 to turn the LED on
ledCharacteristic.writeValue((byte)0x01);
} else {
Serial.println("button released");
// button is released, write 0x00 to turn the LED off
ledCharacteristic.writeValue((byte)0x00);
}
}