gistfile1.txt

@protocol SignalDelegate
- (void)signalDidChange:(Signal*)signal; // change to suit your needs
@end


@interface Signal
@property id<SignalDelegate> delegate;
...
@end


@implementation Signal

...

- timerCallback:(NSTimer:)
{
    [self.delegate signalDidChange:self];
}

@end


@implementation MainViewController

- viewDidLoad;
{
    signal = ...;
    [signal setDelegate:self]
}

- (void)signalDidChange:(Signal*)signal;
{
    // update progress bar
}

@end