一个有趣的教程
转自http://instruct1.cit.cornell.edu/courses/bionb441/Timers/index.html呵呵，最近发现了不少很好的教程，都没时间仔细看
Cornell University
BioNB 441
Using Matlab Timers
Introduction
Matlab 6.5 includes the ability to schedule m-files to run. The scheduling can
be one-shot or repetitive. Scheduling allows (almost) real-time control of
external instruments and recording of electical signals. For instance, it
should be possible to make a software oscilloscope which acquires voltages from
the sound port at regular intervals.
Examples
1. The following program is a simple clock. Every second, the time and date
are updated in a small window. The program uses a very small fraction of the
cpu, and while it is running the command line prompt is active. The figure
CloseRequestfcn is set up to destroy the timer so that when the window is
closed, the timer stops. The timer object is assigned a period, starting delay,
and a call-back string which executes when the timer-object times out.
figure
clf
set(gcf,'position',)
set(gcf,'doublebuffer','on')
set(gcf, 'closerequestfcn','stop(t);delete(t);delete(gcf)');
set(gcf, 'menubar','none')
axes('position',);
%Build Timer object and turn on timer
%delay for 1/2 second so rest of setup finishes
t = timer('period',1.0);
set(t,'ExecutionMode','fixedrate','StartDelay',0.5);
set(t,'timerfcn',['cla;',...
'ct = datestr(clock,''mmm.dd,yyyy HH:MM:SS'');',....
'text(.05,.5,ct,''fontsize'',12);']);
start(t);
2. This example queries a web site once every 10 minutes and sends mail if
the web site is down. It uses the urlread function to check the web site and
the sendmail function to send the mail. Note that you will need to set the
values of your SMTP server and your mail id on that server using the commands
given in the example. You will also need to supply the mail address of the
recepient to sendmail.
figure
clf
set(gcf,'position',)
set(gcf,'doublebuffer','on')
set(gcf, 'closerequestfcn','stop(t);delete(t);delete(gcf)');
set(gcf, 'menubar','none')
setpref('Internet','SMTP_Server','yourSMTPserver.com');
setpref('Internet','E_mail','yourMailID');
axes('position',);
%Build Timer object and turn on timer
%delay for 1/2 second so rest of setup finishes
t = timer('period',600.0);
set(t,'ExecutionMode','fixedrate','StartDelay',0.5);
set(t,'timerfcn',['cla;',...
's=[];s=urlread(''http://www.cornell.edu'');',...
'ct=''Server Up'';',...
'if isempty(s);',...
'ct=''Cornell Server Down'';',...
'sendmail(''user@otherdomain.com'',''Server Down''
,'''');',...
'end;',....
'text(.05,.5,ct,''fontsize'',12);']);
start(t);
3. The next example uses a timer to acquire data from the sound port using
the audiorecorder object. The program is written as a function which is called
by the callbacks. The sound is filtered, and the original spectrum and filtered
spectrum are displayed in a figure. The execution of the timer event callback
takes around 0.10 to 0.25 seconds if the cursor is in any Matlab window, but
takes around 0.05 second if the mouse cursor has been clicked outside of any
Matlab window. The getaudiodata function does not always return the number of
samples that you asked for, but it always returns at least the desired number.
The tic and toc commands in the timer callback function were used to determine
the execution time.
%record and filter as fast as possible
%using Matlab 6.5 timer and audiorecorder functions
function audio1(varargin);
%find out what kind of call it was
%timer event passes {obj,event,param1,param2}
switch nargin
case 0
fcn = 'setup'; %starting up
case 1
fcn = varargin{1}; %quiting
case 4
fcn = varargin{3}; %timer event
otherwise
error('bad agrument');
end
%===========================================================
switch fcn
case 'setup'
data.myname = mfilename ;
fig=figure(1);
clf;
set(fig,'doublebuffer','on');
%sample rate and number of inputs per tirgger
data.Nin = 1024;
data.Fs = 8192;
data.tperiod = data.Nin/data.Fs;
Nchan = 1;
Nbits = 16;
%Configure the Filter
filterlength=8;
%frequencies a a fraction of the nyquist freq
locut=400/(data.Fs/2);
hicut=1200/(data.Fs/2);
= butter(filterlength,);
%plot the filter freq response
= freqz(data.b,data.a,1000);
subplot(3,1,2)
plot(ffreq/pi*data.Fs/2,abs(fresponse));
xlabel('frequency')
ylabel('filter response')
axis();
% Input Object Configuration.
% Create an analog input object with one channel.
data.rec = audiorecorder(data.Fs, Nbits, Nchan);
% Start the analog input object.
%and get the first sample of music
recordblocking(data.rec,data.tperiod);
data.music = getaudiodata(data.rec);
data.filteredmusic = filter(data.b, data.a, data.music);
%Build Timer object and turn on timer
%delay for 1/2 second so rest of setup finishes
data.t = timer('timerFcn',{data.myname,'timer',gcf},...
'period',data.tperiod*2);
set(data.t,'ExecutionMode','fixedrate','StartDelay',0.5);
set(data.t,'tag','time');
start(data.t);
%plot of spectrum of filtered signal
subplot(3,1,3)
=periodogram(data.filteredmusic,[],[],data.Fs);
data.fline=plot(freq,spect);
set(gca,'ylim',);
xlabel('frequency'); ylabel('filtered amp');
%plot of spectrum of raw signal
subplot(3,1,1)
=periodogram(data.music,[],[],data.Fs);
data.iline=plot(freq,spect);
set(gca,'ylim',);
xlabel('frequency'); ylabel('music amp');
%new start the next data aqusition
%after this, the timer routine starts data
record(data.rec,data.tperiod);
%one gui element to stop the music
data.quitbutton=uicontrol('Style','pushbutton',...
'Position',,...
'String','Quit',...
'callback', );
set(fig,'userdata',data);
case 'quit'
data=get(gcf,'userdata');
%stop everything and delete it
stop(data.rec)
delete(data.rec)
stop(data.t)
delete(data.t)
close(gcf);
case 'timer'
tic
data=get(varargin{4},'userdata');
%get data from recording started last time
while isrecording(data.rec)
end
data.music = getaudiodata(data.rec);
data.music = data.music(1:data.Nin);
% Start recording new data.
record(data.rec,data.tperiod);
% compute the spectrum and display it
spect = periodogram(data.music,[],[],data.Fs);
set(data.iline,'ydata',spect);
%filter it , compute the spectrum and display
data.filteredmusic = filter(data.b,data.a,data.music) ;
spect=periodogram(data.filteredmusic,[],[],data.Fs);
set(data.fline,'ydata',spect);
set(varargin{4},'userdata',data);
toc
end 比较有参考价值，虽然用其他的语言也能实现，MATLAB功能还是很强大。
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