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
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',[10 50 175 35])
set(gcf,'doublebuffer','on')
set(gcf, 'closerequestfcn','stop(t);delete(t);delete(gcf)');
set(gcf, 'menubar','none')
axes('position',[0 0 1 1 ]);
%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);
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',[10 50 175 35])
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',[0 0 1 1 ]);
%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);
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);
[data.b,data.a] = butter(filterlength,[locut,hicut]);
%plot the filter freq response
[fresponse, ffreq] = freqz(data.b,data.a,1000);
subplot(3,1,2)
plot(ffreq/pi*data.Fs/2,abs(fresponse));
xlabel('frequency')
ylabel('filter response')
axis([0 data.Fs/2 0 2]);
% 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)
[spect,freq]=periodogram(data.filteredmusic,[],[],data.Fs);
data.fline=plot(freq,spect);
set(gca,'ylim',[0 .001]);
xlabel('frequency'); ylabel('filtered amp');
%plot of spectrum of raw signal
subplot(3,1,1)
[spect,freq]=periodogram(data.music,[],[],data.Fs);
data.iline=plot(freq,spect);
set(gca,'ylim',[0 .001]);
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',[0 0 45 25],...
'String','Quit',...
'callback', [data.myname,' quit']);
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