Help with timing a pushbutton being pushed twice

So i'm trying to find the time interval between a single push button when pushed twice.. here is my code so far. This is for a GUI btw

% Choose default command line output for BW2
handles.output = hObject;
set(handles.pushbutton1, 'UserData', 0);
setappdata(handles.text11, 'text11', 0);
setappdata(handles.text12, 'STARTING', 0);
setappdata(handles.text13, 'FINISH', 0);

% Update handles structure
guidata(hObject, handles);
handles.gx= 0;
handles.gy= 0;

% UIWAIT makes BW2 wait for user response (see UIRESUME)
% uiwait(handles.figure1);

% --- Outputs from this function are returned to the command line.
function varargout = BW2_OutputFcn(hObject, eventdata, handles) 
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)

counter = get(hObject, 'UserData') + 1;
set(hObject, 'UserData', counter);
set(handles.text1, 'String', sprintf('%d', counter));

set(handles.text8,'String',datestr(now));

if mod(counter,2)
c = clock; 
seconds = c(6);
setappdata(handles.text12, 'STARTING', seconds);
guidata(hObject, handles);
else
    c = clock; 
    seconds = c(6);
    setappdata(handles.text13, 'FINISH', seconds);
    guidata(hObject, handles);
end

before = getappdata(handles.text12, 'STARTING');
after = getappdata(handles.text13, 'FINISH');
interval = (after-before)

if (interval < 5)
    bpm = (2/interval)*(60/1);
    set(handles.text11, 'string', bpm);
end

the problem starts under the pushbutton callback. i'm basically reading in values every time they're even or odd and measuring time between each click. My first value is always something huge like 50+ seconds, and every other value is negative.

[Amed]

anything?

Answer 1

[Kye Taylor]

Computing the time elapsed between two date vectors is nontrivial, I bet you're getting some weird behavior here. Try using the etime function

t = clock
elapsedTime = etime(clock,t);

If you include the line

handles.startTime = [];

in the *_OpeningFcn callback, then the following is an example of a callback that will spit out the elapsed time between pushing the pushbutton:

function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

if isempty(handles.startTime)
    handles.startTime = clock;
else
    % get elapsed time
    elapsedTime = etime(clock, handles.startTime);

    % reset
    handles.startTime = [];

    % display elapsed time
    disp(elapsedTime)
end

guidata(hObject, handles);

[Sean de Wolski]

I guess I don't understand why you wouldn't just use tic/toc

t = tic;

toc(t)

[Kye Taylor]

That would work, but may not be as robust, since tic may be called at some other point in the application, or from the command line.

Plus, how could he tell if the timer was "started" or not? (this is what I'm doing with the isempty function).. a variable would need to be created to keep track of the state (started or not)

[Sean de Wolski]

Yes. I would do all of this in an object but that's a different story.

Anyway, it doesn't matter if tic is started elsewhere. You can have the handle to a specific tic. Consider this:

t = tic;
pause(4);
tt=tic;
toc(t);
toc(tt);

[Kye Taylor]

Well.. once he figures out how to keep track of the state, and either pass around the outputs from tic or make them persistent, the tic/toc commands you mention are viable. I didn't realize toc could take inputs. sweet.

Answer 2

[Amed]

Thanks guys I will check the answers when i'm back from class.

In terms of getting strange answers, i'm getting normal absolute values (except for the first value, seems to be random or some sorts?), but afterwards the intervals ARE correct. If I can just somehow void the first value and then take the absolute values before converting the time (s) into (beats/minute)

As for tic/toc functions, I couldn't get them to measure two separate push's on the same exact button. They read out twin numbers each time.