How to detect keyboard spacebar press in matlab？ - matlab

Question

I want to detect how many times the user click spacebar in 5 seconds
Is there any good way to fix this problem?
Thanks

Answer 1

One way to easily read user inputs from the keyboard is to create a new figure and specify a KeyPressFcn callback function, which is executed automatically if any key is pressed.
Lets start off by creating a new figure. As we don't need the figure to display anything, let's make it as small as possible (i.e. 1 by 1 pixel) and place it at the lower corner of the display:
f = figure('Position',[0,0,1,1]);
Now we'll set the UserData property of the figure - which we will use as counter - to zero:
set(f,'UserData',0);
Now let's see what to do when a key is pressed: We can create a small callback function which checks if the pressed button was a space and increases the UserData counter if that was the case. We'll call that function isspace:
function isspace(hObject,callbackData)
if get(hObject,'CurrentCharacter') == ' '
set(hObject,'UserData',get(hObject,'UserData')+1);
end
end
Now simply set up the figure to use this function as KeyPressFcn by
set(f,'KeyPressFcn',#isspace);
This already counts the number of times space is pressed. The current value of the counter is read by
get(f,'UserData');
Now we need the time measurement. This can be done using a timer. We'll configure it to go off after 5 seconds and then assing a new value in the base workspace. For that we need a callback function timerCallback.m
function timerCallback(hObj,eventData)
assignin('base','nSpace',get(gcf,'UserData'));
delete(gcf);
stop(hObj);
delete(hObj);
end
t = timer('StartDelay',5,'TimerFcn',#timerCallback);
start(t);
And that's it: First create the figure, create the timer and after 5 seconds you get the number of key presses in the variable nSpace in your workspace and the window is closed.