YmsCoreBluetooth v1.09

A block-based framework for building Bluetooth 4.0 Low Energy (aka Smart or LE) iOS 7 or OS X 10.9 applications using the CoreBluetooth API. Includes Deanna and DeannaMac, applications to communicate with a TI SensorTag for iOS and OS X respectively.

YmsCoreBluetooth Design Intent: Or Why You Want To Use This Framework


  • ObjectiveC Block-based API for Bluetooth LE communication.
  • Operations (e.g. scanning, retrieval, connection, reads, writes) map to the data object hierarchy of CoreBluetooth.
  • You can build apps using CoreBluetooth faster.

A More Detailed Explanation

Blocks are cool.

Transactions in Bluetooth LE (BLE) are two-phase (request-response) in nature: CoreBluetooth abstracts this protocol so that request behavior is separated from response behavior. The two phases are reconciled using a delegation pattern: the object initiating the request phase has a delegate object with a delegate method to handle the corresponding response phase. While functional, the delegation pattern can be cumbersome to use because the behavior for a two-phase transaction is split into two different locations in code.

A more convenient programming pattern is to use a callback block which is defined with the request. When the response is received, the callback block can be executed to handle it. The design intent of YmsCoreBluetooth is use Objective-C blocks to define response behavior to BLE requests. Such requests include:

  • scanning and/or retrieving peripheral(s)
  • connecting to a peripheral
  • discovering a peripheral's services
  • discovering a service's characteristics
  • write and read of a characteristic
  • setting the notification status of a characteristic

Hierarchical operations are cool.

The data object hierachy of CoreBluetooth can be described as such:

  • A CBCentralManager instance can connect to multiple CBPeripheral instances.
    • A CBPeripheral instance can have multiple CBService instances.
      • A CBService instance can have multiple CBCharacteristic instances.
        • A CBCharacteristic instance can have multiple CBDescriptor instances.

However the existing CoreBluetooth API does not map BLE requests to the data object hierarchy. For example connection to a CBPeripheral instance is accomplished from a CBCentralManager instance instead of from a CBPeripheral. Writes, reads, and setting the notification state of a CBCharacteristic are issued from a CBPeripheral instance, instead of from CBCharacteristic. YmsCoreBluetooth provides an API that more naturally maps operations to the data object hierarchy.

YMSCoreBluetooth defines container classes which map to the CoreBluetooth object hierarchy:

  • YMSCBCentralManager - Contains a CBCentralManager instance.
    • YMSCBPeripheral - Contains a CBPeripheral instance.
      • YMSCBService - Contains a CBService instance.
        • YMSCBCharacteristic - Contains a CBCharacteristic instance.
          • YMSCBDescriptor - Contains a CBDescriptor instance.

However, they differ from CoreBluetooth in that operations are done with respect to the object type:

  • YMSCBCentralManager
    • scans for peripherals
    • retrieves peripherals
  • YMSCBPeripheral
    • connects and disconnects to central
    • discovers services associated with this peripheral
  • YMSCBService
    • discovers characteristics associated with this service
    • handles notification updates for characteristics which are set to notify
  • YMSCBCharacteristic
    • set notification status (on, off)
    • write value to characteristic
    • read value of characteristic
    • discover descriptors associated with this characteristic
  • YMSCBDescriptor
    • write value to descriptor
    • read value of descriptor

Deanna and DeannaMac

The apps Deanna and DeannaMac are demonstration apps intended to illustrate the use of YmsCoreBluetooth. Both apps use YmsCoreBluetooth to characterize a TI SensorTag and provide controllability and observability of the six sensors on the device. It also has the capability to scan for other BLE devices.

Deanna has been recently changed (v 0.943) to support the graphic design contributions of Wayne Dahlberg.

Show Code

Scanning for Peripherals

In the following code sample, self is an instance of a subclass of YMSCBCentralManager.

__weak DEACentralManager *this = self;
[self scanForPeripheralsWithServices:nil
                           withBlock:^(CBPeripheral *peripheral, NSDictionary *advertisementData, NSNumber *RSSI, NSError *error) {
                               if (error) {
                                   NSLog(@"Something bad happened with scanForPeripheralWithServices:options:withBlock:");

                               NSLog(@"DISCOVERED: %@, %@, %@ db", peripheral, peripheral.name, RSSI);
                               [this handleFoundPeripheral:peripheral];

Retrieving Peripherals

In the following code sample, self is an instance of a subclass of YMSCBCentralManager and identifiers is an array of NSUUID instances that map to a peripheral that has been discovered by the iOS device.

[self retrievePeripheralsWithIdentifiers:identifiers];

Note - This API has changed for iOS7 due to the deprecation of [YMSCBCentralManager retrievePeripherals:withBlock:]

__weak DEACentralManager *this = self;
[self retrievePeripherals:peripheralUUIDs
                withBlock:^(CBPeripheral *peripheral) {
                    [this handleFoundPeripheral:peripheral];

Connecting to a Peripheral

In the following code sample, self is an instance of a subclass of YMSCBPeripheral. Note that in the callbacks, discovering services and characteristics are handled in a nested fashion:

- (void)connect {
    // Watchdog aware method
    [self resetWatchdog];

    [self connectWithOptions:nil withBlock:^(YMSCBPeripheral *yp, NSError *error) {
        if (error) {

        // Example where only a subset of services is to be discovered.
        //[yp discoverServices:[yp servicesSubset:@[@"temperature", @"simplekeys", @"devinfo"]] withBlock:^(NSArray *yservices, NSError *error) {

        [yp discoverServices:[yp services] withBlock:^(NSArray *yservices, NSError *error) {
            if (error) {

            for (YMSCBService *service in yservices) {
                if ([service.name isEqualToString:@"simplekeys"]) {
                    __weak DEASimpleKeysService *thisService = (DEASimpleKeysService *)service;
                    [service discoverCharacteristics:[service characteristics] withBlock:^(NSDictionary *chDict, NSError *error) {
                        [thisService turnOn];

                } else if ([service.name isEqualToString:@"devinfo"]) {
                    __weak DEADeviceInfoService *thisService = (DEADeviceInfoService *)service;
                    [service discoverCharacteristics:[service characteristics] withBlock:^(NSDictionary *chDict, NSError *error) {
                        [thisService readDeviceInfo];

                } else {
                    __weak DEABaseService *thisService = (DEABaseService *)service;
                    [service discoverCharacteristics:[service characteristics] withBlock:^(NSDictionary *chDict, NSError *error) {
                        for (NSString *key in chDict) {
                            YMSCBCharacteristic *ct = chDict[key];
                            //NSLog(@"%@ %@ %@", ct, ct.cbCharacteristic, ct.uuid);

                            [ct discoverDescriptorsWithBlock:^(NSArray *ydescriptors, NSError *error) {
                                if (error) {
                                for (YMSCBDescriptor *yd in ydescriptors) {
                                    NSLog(@"Descriptor: %@ %@ %@", thisService.name, yd.UUID, yd.cbDescriptor);

Read a Characteristic

In the following code sample, self is an instance of a subclass of YMSCBService. All discovered characteristics are stored in [YMSCBService characteristicDict].

- (void)readDeviceInfo {

    YMSCBCharacteristic *system_idCt = self.characteristicDict[@"system_id"];
    __weak DEADeviceInfoService *this = self;
    [system_idCt readValueWithBlock:^(NSData *data, NSError *error) {
        NSMutableString *tmpString = [NSMutableString stringWithFormat:@""];
        unsigned char bytes[data.length];
        [data getBytes:bytes];
        for (int ii = (int)data.length; ii >= 0;ii--) {
            [tmpString appendFormat:@"%02hhx",bytes[ii]];
            if (ii) {
                [tmpString appendFormat:@":"];

        NSLog(@"system id: %@", tmpString);
            this.system_id = tmpString;


    YMSCBCharacteristic *model_numberCt = self.characteristicDict[@"model_number"];
    [model_numberCt readValueWithBlock:^(NSData *data, NSError *error) {
        if (error) {
            NSLog(@"ERROR: %@", error);

        NSString *payload = [[NSString alloc] initWithData:data encoding:NSStringEncodingConversionAllowLossy];
        NSLog(@"model number: %@", payload);
            this.model_number = payload;

Write to a Characteristic

In the following code sample, self is an instance of a subclass of YMSCBService. In this example, a write to the 'config' characteristic followed by a read of the 'calibration' characteristic is done.

- (void)requestCalibration {
    if (self.isCalibrating == NO) {

        __weak DEABarometerService *this = self;

        YMSCBCharacteristic *configCt = self.characteristicDict[@"config"];
        [configCt writeByte:0x2 withBlock:^(NSError *error) {
            if (error) {
                NSLog(@"ERROR: write request to barometer config to start calibration failed.");

            YMSCBCharacteristic *calibrationCt = this.characteristicDict[@"calibration"];
            [calibrationCt readValueWithBlock:^(NSData *data, NSError *error) {
                if (error) {
                    NSLog(@"ERROR: read request to barometer calibration failed.");

                this.isCalibrating = NO;
                char val[data.length];
                [data getBytes:&val length:data.length];

                int i = 0;
                while (i < data.length) {
                    uint16_t lo = val[i];
                    uint16_t hi = val[i+1];
                    uint16_t cx = ((lo & 0xff)| ((hi << 8) & 0xff00));
                    int index = i/2 + 1;

                    if (index == 1) self.c1 = cx;
                    else if (index == 2) this.c2 = cx;
                    else if (index == 3) this.c3 = cx;
                    else if (index == 4) this.c4 = cx;
                    else if (index == 5) this.c5 = cx;
                    else if (index == 6) this.c6 = cx;
                    else if (index == 7) this.c7 = cx;
                    else if (index == 8) this.c8 = cx;

                    i = i + 2;

                this.isCalibrating = YES;
                this.isCalibrated = YES;



Handling Characteristic Notification Updates

One place where YmsCoreBluetooth does not use blocks to handle BLE responses is with characteristic notification updates. The reason for this is because such updates are asynchronous and non-deterministic. As such the handler method [YMSCBService notifyCharacteristicHandler:error:] must be implemented for any subclass of YMSCBService to handle such updates.

In the following code sample, self is an instance of a subclass of YMSCBService.

- (void)turnOn {
    __weak DEABaseService *this = self;

    YMSCBCharacteristic *configCt = self.characteristicDict[@"config"];
    [configCt writeByte:0x1 withBlock:^(NSError *error) {
        if (error) {
            NSLog(@"ERROR: %@", error);

        NSLog(@"TURNED ON: %@", this.name);

    YMSCBCharacteristic *dataCt = self.characteristicDict[@"data"];
    [dataCt setNotifyValue:YES withBlock:^(NSError *error) {
        NSLog(@"Data notification for %@ on", this.name);

        this.isOn = YES;

- (void)notifyCharacteristicHandler:(YMSCBCharacteristic *)yc error:(NSError *)error {
    if (error) {

    if ([yc.name isEqualToString:@"data"]) {
        NSData *data = yc.cbCharacteristic.value;

        char val[data.length];
        [data getBytes:&val length:data.length];

        int16_t v0 = val[0];
        int16_t v1 = val[1];
        int16_t v2 = val[2];
        int16_t v3 = val[3];

        int16_t amb = ((v2 & 0xff)| ((v3 << 8) & 0xff00));
        int16_t objT = ((v0 & 0xff)| ((v1 << 8) & 0xff00));

        double tempAmb = calcTmpLocal(amb);

        __weak DEATemperatureService *this = self;
            this.ambientTemp = @(tempAmb);
            this.objectTemp = @(calcTmpTarget(objT, tempAmb));

Important: To let the UI components in the main thread know via KVO that a property has changed, you must update that property on the main thread. A convenience macro _YMS_PERFORM_ON_MAIN_THREAD which uses the GCD call dispatch_async() does just that:

#define _YMS_PERFORM_ON_MAIN_THREAD(block) dispatch_async(dispatch_get_main_queue(), block);

Block Callback Design

The callback pattern used by YmsCoreBluetooth uses a single callback to handle both successfull and failed responses. This is accomplished by including an error parameter. If an error object is not nil, then behavior to handle the failure can be implemented. Otherwise behavior to handle success is implemented.

^(NSError *error) {
   if (error) {
      // Code to handle failure
   // Code to handle success

File Naming Conventions

The YmsCoreBluetooth framework is the set of files prefixed with YMSCB located in the directory YmsCoreBluetooth.

The files for the iOS application Deanna are prefixed with DEA and are located in the directory Deanna.

The files for the OS X application DeannaMac are prefixed with DEM and are located in the directory DeannaMac.

Recommended Code Walk Through

To better understand how YmsCoreBluetooth works, it is recommended to first read the source of the following BLE service implementations:

  • DEAAccelerometerService, DEABarometerService, DEAGyroscopeService, DEAHumidityService, DEAMagnetometerService, DEASimpleKeysService, DEATemperatureService, DEADeviceInfoService

Then the BLE peripheral implementation of the TI SensorTag:

  • DEASensorTag

Then the application service which manages all known peripherals:

  • DEACentralManager

The Class Hierarchy is very instructive in showing the relationship of the above classes to the YmsCoreBluetooth framework.

Writing your own Bluetooth LE service with YmsCoreBluetooth

Learn how to write your own Bluetooth LE service by reading the example of how its done for the TI SensorTag in the Tutorial.


While YmsCoreBluetooth is quite functional, there's always room for improvement. Please submit any questions or issues to the GitHub project for YmsCoreBluetooth.

Are you using YmsCoreBluetooth? Let us know!

I'm working on publishing a list of projects using YmsCoreBluetooth. If you're not shy about this, please let me know and thank you for using YmsCoreBluetooth! And even if you are shy, please let me know and I promise full discretion.


Code tested on:

  • iPhone 4S, iPod touch, iPhone 5 all running iOS7
  • TI SensorTag firmware 1.2, 1.3
  • iMac 27 Mid-2010, OS X 10.8.5

Known Issues

  • Use this code only on iOS or Mac hardware that supports CoreBluetooth. The iOS Simulator is not supported.

Latest Changes

Mon Jan 13 2014

Added methods to support BLE addressing:

  • initWithName:parent:baseHi:baseLo:serviceBLEOffset:
  • addCharacteristic:withBLEOffset:

Wed Jan 1 2014

  • #97 - Add [YMSCBPeripheral readRSSI] method
  • #98 - Make objectForKeyedSubscript: a public method for YMSCBPeripheral and YMSCBService
  • #96 - Add [YMSCBPeripheral name] convenience accessor to cbPeripheral.name

Mon Dec 2 2013

  • #92 - Reimplement [YMSCBCentralManager count] to use KVO collection method.
  • #94 - Implement [YMSCBCentralManager removeAllPeripherals] method.

Tested Mac Environment:

  • OS X 10.8.3
  • iMac 27 Mid-2010

View Prior Change List


Copyright 2013-2014 Yummy Melon Software LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.

Author: Charles Y. Choi <charles.choi@yummymelon.com>