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Logging only transition points

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Logging only transition points

Postby ECS » Thu Jun 12, 2014 12:13 pm

Dear All
I would appreciate you help on the following: :(
I have a screen flickering between a black and white image at a rate of 1 Hz i.e 2 reversals per second. However, I need to know how stable this flicker is down to the millisecond (preferably 1ms)

I set up a photodiode light sensor which is signal conditioned (Schmit trigger) to produce a clean square wave. I now need to log data only at the point of transition from black to white and from white to black with millisecond timing precision while ommiting the periods in between.

The picoscope has an excellent set of triggering options which is somewhat limited with picolog software. The recent picoscope software allows triggering at BOTH the rising and falling edge of the pulse which is exactly what I need for this problem but this is not allowed in picolog which allows either the rising OR falling edge triggering. (any solution - I have a Picoscope 2205 and a Picolog 1000 series and a DrDAQ.)

Having configured the system to monitor at 1ms interval how do I log data ONLY at the transition points and not during the steady state intervals in between the transitions. I can then import this data into excel and analyse.

Presently I'm getting a long string of thousands of lines of data eg. (0V,...0,2...,2,0...0,2...2,0,........volts..and so on). I then have to isolate the transitions by manually finding and deleting all the steady state entries - (strings of '0' or '2' ) but locate only the entries where the voltage changes (0-->2 or 2-->0) which indicates a transition. As Picolog allows logging at only either the rising OR the falling edge, using picoscope would be ideal as the triggers are more versatile, but actually outputting the data to a file then becomes the limitation - I am unable to do this.

As this is a time consuming process I urgently need a way obtain the data as explained above. There should be a simple way to log data only when a transition occurs. Nothing I have tried so far works. They all produce thousand of lines of entries when I am only interested in the transition points and precisely when this occurs.

2. Also: Is it possible to output data directly from the picoscope into a notepad file and not have to use the picolog. As I mentioned earlier, the picoscope triggers are more versatile while the picolog triggers are quite limited.

I need this information quite urgently for my research and would therefore appreciate your help
Many thanks
ECS
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Re: Logging only transition points

Postby Martyn » Fri Jun 13, 2014 1:26 pm

If you are looking at the stability of the edges, with reference to the frequency of transitions, then you will need to know exactly how many samples occur between the edges, there is no real time timestamping for trigger at the present time.

Picoscope can be configured to export data to csv or txt files on alarm conditions, such as "Complete Capture", "Buffers Full", or "Mask Fail", this feature can be found under Tools->Alarms.
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Re: Logging only transition points

Postby ECS » Tue Jun 17, 2014 11:54 am

Thank you Martyn - I think essentially what I want to do is to be able to export only the log immediately after a transition occurs. I'm reasonably sure the rise and fall time on the square wave is very much less thank a millisecond so only very rarely would the log fall during this brief interval. For example - this will eventually enable tell me to report that "the screen is flickering at 1Hz with a 'mean jitter' of say 15 ms, standard deviation of 5ms and long term drift of 120ms over a period of 3minutes. That's the sort of info I am looking to obtain.
I did some experimenting with the alarms and masks but exporting the data to be able to report like the above example is quite cumbersome.
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Re: Logging only transition points

Postby Martyn » Tue Jun 24, 2014 7:44 am

To get the timing of the transition points, but only have the data just around the edges, you will probably need to write your own application using the SDK.

I can't think of a neat way of doing this using the PicoScope or PicoLog programs as both would require the full data to be captured to get the timing between transitions.
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