Event triggered square-wave

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Yigit
Yigit on 22 Nov 2011
hi,
I generate square wave signal with this ;
freq_Hz = 30;
t = 0:0.0001:10;
y = square(2*pi*freq_Hz*t);
plot(t,y);
axis([0 10 -1.5 1.5]);
xlabel('Seconds');
ylabel('Amplitude');
But I want to trigger each duty cycle with an external event. Like this in pseudo ;
for i:1:100
if event1=1
pwm(i) = high
if event2=0
pwm(i) = low
plot(i,pwm)i)
but can't interfere to square function.
I am sure experienced users will provide some insight.

Answers (1)

Walter Roberson
Walter Roberson on 22 Nov 2011
I just wrote several paragraphs with specific references to why it cannot be done. You deleted the question out from underneath me, so my write-up was lost. This is frustrating to say the least. So you can dig the reasoning out yourself, and you are lucky I still had the documents in my cache.
  4 Comments
Yigit
Yigit on 23 Nov 2011
PC (laptop);
Intel Core2Duo 2.6 Ghz
4GB OCZ Ram (2x2GB)
Nvidia 9300M GS Graphics Acc (CUDA)
Data Acqusition ;
Arduino uno board interfaced with LTC2485CDD via SPI(24bit ADC). Running at 115200 as serial object.
Environment ;
Matlab 2011a 32bit, Slackware Linux 13.37. System is multilib but I prefer 32bit version.
I can't get data acquisition working through the DATA AQ toolbox, I read data the conventional way (m-file).
I use Psychtoolbox (PTB3) to blink the screen (visual stimulus) at a determined frequency and correlate the results obtained from data acquisition. Is there a way to blink the screen flash (fullscreen) at a determined frequency without using a toolbox ? I am sure matlab is capable of doing this, I just couldn't figure out how to. PTB3 introduces too much delay between functions and I just use it to blink the screen.
I need max of 300samples/sec (300Hz), it shouldn't be that hard I suppose ?
Walter Roberson
Walter Roberson on 23 Nov 2011
The LTC2485CDD normally runs at a maximum of 60 Hz, though there seems to be a "2x speedup mode" possible with it. You will not be able to obtain 300 Hz with it.
MATLAB has no facilities to blink the screen.
PTB3 claims up to 2 KHz sample rate (12 bit) sample rate with a Measurement Computing USB-based interface; see http://docs.psychtoolbox.org/Daq
What is the maximum frame rate for your display? It was never very common to find a CRT with higher than 85 Hz (except for the 120 Hz stereo modes), and most LCD are 60 Hz or lower. CRT often require a notable time to reconfigure to different frame rates (which often require resolution changes), and on most monitors the workable frame rates are a fairly small list. If you have an especially forgiving monitor sometimes you can design custom front porch timings and the like to fine-tune frame rates; Linux does seem to be the OS to use for that kind of work, but it can be tricky work and risks monitor damage if you get it wrong; a high level of attention to detail is necessary. Custom video formats pretty much have to be designed in advance.
Switching video formats using the official mechanisms is not a light-weight change, as the X11 driver has to be notified of the changes and reconfigures its ideas of your screen sizes, perhaps repositions your icons, etc.

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