Exemplo de código Objective-C

BluetoothWriter.h

#import <Foundation/Foundation.h>
#import <CoreBluetooth/CoreBluetooth.h>

@interface BluetoothWriter : NSObject

-(id) initWithPeripheral:(CBPeripheral *) peripheral characteristic:(CBCharacteristic *)characteristic;

- (void) writeString:(NSString *) value;
- (void) writeData:(NSData *) value;
-(void) writeColorWithRed:(int)red withGreen:(int)green withBlue:(int)blue;

@end

BluetoothWriter.m

#import "BluetoothWriter.h"

@interface BluetoothWriter (){
    
}

@property (weak, nonatomic) CBPeripheral *peripheral;
@property (weak, nonatomic) CBCharacteristic *characteristic;

@end

@implementation BluetoothWriter

-(id) initWithPeripheral:(CBPeripheral *)per characteristic:(CBCharacteristic *)charac{
    if ((self = [super init])) {
        self.peripheral = per;
        self.characteristic = charac;
    }
    return self;
}

-(void) writeData:(NSData *)value{
    if (self.peripheral != nil && self.characteristic != nil) {
        [self.peripheral writeValue:value forCharacteristic:self.characteristic type:CBCharacteristicWriteWithoutResponse];
    }
}

-(void) writeString:(NSString *)value{
    [self writeData:[value dataUsingEncoding:NSUTF8StringEncoding]];
}

-(void) writeColorWithRed:(int)red withGreen:(int)green withBlue:(int)blue{
    [self writeString:[NSString stringWithFormat:@"c%d,%d,%d\n",red,green,blue]];
}

@end