In the following BLE example: I would like to separate a floating point number into elements that I could assign into the CUSTOM_UUID.
For example: Take 12345.67 and somehow assign it into the CUSTOM_UUID[] as
const uint8_t CUSTOM_UUID[] =
{
0X00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x01, 0x32, 0x54, 0x67
};
BLEUuid uuid = BLEUuid(CUSTOM_UUID);
The current format appears in the BLE advertisement as: 00000000-0000-0000-0000-000000000000 so I would like to get to something like: 00000000-0000-0000-0000-000001234567 as a first step. Next step will be dealing with the decimal.
/*********************************************************************
This is an example for our nRF52 based Bluefruit LE modules
Pick one up today in the adafruit shop!
Adafruit invests time and resources providing this open source code,
please support Adafruit and open-source hardware by purchasing
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MIT license, check LICENSE for more information
All text above, and the splash screen below must be included in
any redistribution
Author: KTOWN (Kevin Townsend)
Copyright (C) Adafruit Industries 2017
*********************************************************************/
/* This example constantly advertises a custom 128-bit UUID, and is
* intended to be used in combination with a Central sketch that scans
* for this UUID, and then displays an alert message, sorting matching
* devices by their RSSI level which is an approximate indication of
* distance (although highly subject to environmental obstacles).
*
* By including a custom UUID in the advertising packet, we can easily
* filter the scan results on the Central device, rather than manually
* parsing the advertising packet(s) of every device in range.
*
* This example is intended to be run with the *_central.ino version
* of this application.
*/
#include <bluefruit.h>
#include <ble_gap.h>
//int test_hex = 0x55;
// Software Timer for blinking RED LED
SoftwareTimer blinkTimer;
// Custom UUID used to differentiate this device.
// Use any online UUID generator to generate a valid UUID.
// Note that the byte order is reversed ... CUSTOM_UUID
// below corresponds to the follow value:
// df67ff1a-718f-11e7-8cf7-a6006ad3dba0
const uint8_t CUSTOM_UUID[] =
{
0X00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};
BLEUuid uuid = BLEUuid(CUSTOM_UUID);
void setup()
{
Serial.begin(115200);
while ( !Serial ) delay(10); // for nrf52840 with native usb
Serial.println("Bluefruit52 Peripheral Proximity Example");
Serial.println("----------------------------------------\n");
// Initialize blinkTimer for 1000 ms and start it
blinkTimer.begin(1000, blink_timer_callback);
blinkTimer.start();
err_t err = Bluefruit.begin();
if (err)
{
Serial.print("Unable to init Bluefruit (ERROR CODE: ");
Serial.print(err);
Serial.println(")");
while(1)
{
digitalToggle(LED_RED);
delay(100);
}
}
else
{
Serial.println("Bluefruit initialized (peripheral mode)");
}
// Set max power. Accepted values are: -40, -30, -20, -16, -12, -8, -4, 0, 4
Bluefruit.setTxPower(4);
Bluefruit.setName("Bluefruit52");
// Set up and start advertising
startAdv();
Serial.println("Advertising started");
}
void startAdv(void)
{
// Note: The entire advertising packet is limited to 31 bytes!
// Advertising packet
Bluefruit.Advertising.addFlags(BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE);
Bluefruit.Advertising.addTxPower();
// Preferred Solution: Add a custom UUID to the advertising payload, which
// we will look for on the Central side via Bluefruit.Scanner.filterUuid(uuid);
// A valid 128-bit UUID can be generated online with almost no chance of conflict
// with another device or etup
Bluefruit.Advertising.addUuid(uuid);
// Alternative Solution: Manufacturer Specific Data (MSD)
// You could also send a custom MSD payload and filter for the 'Company ID'
// via 'Bluefruit.Scanner.filterMSD(CID);', although this does require a
// valid CID, which is why the UUID method above is more appropriate in
// most situations. For a complete list of valid company IDs see:
// https://www.bluetooth.com/specifications/assigned-numbers/company-identifiers
// For test purposes, 0xFFFF CAN be used, but according to the Bluetooth SIG:
// > "This value may be used in the internal and interoperability tests before a
// > Company ID has been assigned. This value shall not be used in shipping end
// > products."
uint8_t msd_payload[4]; // Two bytes are required for the CID, so we have 2 bytes user data, expand as needed
uint16_t msd_cid = 0xFFFF;
memset(msd_payload, 0, sizeof(msd_payload));
memcpy(msd_payload, (uint8_t*)&msd_cid, sizeof(msd_cid));
msd_payload[2] = 0x11;
msd_payload[3] = 0x22;
Bluefruit.Advertising.addData(BLE_GAP_AD_TYPE_MANUFACTURER_SPECIFIC_DATA, msd_payload, sizeof(msd_payload));
// Not enough room in the advertising packet for name
// so store it in the Scan Response instead
Bluefruit.ScanResponse.addName();
/* Start Advertising
* - Enable auto advertising if disconnected
* - Interval: fast mode = 20 ms, slow mode = 152.5 ms
* - Timeout for fast mode is 30 seconds
* - Start(timeout) with timeout = 0 will advertise forever (until connected)
*
* For recommended advertising interval
* https://developer.apple.com/library/content/qa/qa1931/_index.html
*/
Bluefruit.Advertising.restartOnDisconnect(true);
Bluefruit.Advertising.setInterval(32, 244); // in units of 0.625 ms
Bluefruit.Advertising.setFastTimeout(30); // number of seconds in fast mode
Bluefruit.Advertising.start();
}
void loop()
{
}
/**
* Software Timer callback is invoked via a built-in FreeRTOS thread with
* minimal stack size. Therefore it should be as simple as possible. If
* a periodically heavy task is needed, please use Scheduler.startLoop() to
* create a dedicated task for it.
*
* More information http://www.freertos.org/RTOS-software-timer.html
*/
void blink_timer_callback(TimerHandle_t xTimerID)
{
(void) xTimerID;
digitalToggle(LED_RED);
}
This is an interesting way to get a little more bandwidth out of an advertising packet, but it goes against the intended use of the UUIDs, which are to identify a peripheral's service profiles and available characteristics. (I'm assuming you intend to dynamically generate UUIDs based on some floating point sensor value.)
Having a changing UUID will cause a great deal of trouble when you try to connect to your device using the BLE communication stack of the Central (master) device, e.g. an Android or IOS phone. BLE Central devices expect to gather a static hierarchy of characteristic UUIDs from a given peripheral device, then use those UUIDs to identify the corresponding characteristic values. For example, the IOS BLE stack has constants to identify these well-known advertisement UUIDs, all available before connecting: CBAdvertisementDataLocalNameKey, CBAdvertisementDataManufacturerDataKey, CBAdvertisementDataServiceUUIDsKey, CBAdvertisementDataSolicitedServiceUUIDsKey.
Instead, note that Generic Attribute Profiles include data typing, allowing you to directly set and recover float and double float IEEE-754 floating-point characteristic values, as well as fixed point characteristic types which might better serve your purpose.
Search the docs on your host BLE stack for "Characteristic Presentation Format Descriptor" to find the constants used to identify the type.
I'd suggest that you spend some time studying iOS or Android code samples for BLE communications, and the various Bluetooth/GATT tutorials which describe the hierarchical structure of a BLE device's profiles. Find a cheap BLE device which conforms to one of the GATT profiles here: https://www.bluetooth.com/specifications/gatt (You may need to create a free account.) and experiment with contacting it from your phone or PC. Alternately, see if you can find sample Arduino code which makes the device conform to a well-known GATT profile, and use that as your peripheral.