Products > Test Equipment

Standardised Way To Test Oscilloscope Screen Update Rate

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m k:
Is strobo light mentioned.
It can at least artificially freeze something.

joeqsmith:

--- Quote from: radiolistener on April 30, 2024, 01:23:51 pm ---I think it will be hard to determine refresh rate from high speed video camera capture of the display pixels change, because display has some limited pixel change speed. If there is a way to attach external display it will be better to analyze video signal.

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Odd, seemed easy enough to detect.  Only problem was manually going through the data.   


--- Quote from: bdunham7 on April 30, 2024, 01:42:45 pm ---
--- Quote from: joeqsmith on April 30, 2024, 12:47:43 pm ---Your video requires some codec I don't have.

--- End quote ---

That's Windows pissing in your ear and telling you that it is raining.  HEVC (h265) has been around for quite a while now, but MS still wants a fee to let you use it.  Download VideoLan if you want a decent video viewer.

https://www.videolan.org/vlc/download-windows.html

--- End quote ---

Installed and running. I remember that icon (assume same software) from 20 years ago.  Not a fan of the MS media viewer anyway.   


--- Quote from: bdunham7 on April 30, 2024, 01:42:45 pm ---
--- Quote ---
It seems to stutter or stall at times and then plays catch up.  I had turned off all the readouts and such and set the scope software to the highest screen priority but with Windows not being a RTOS, I am not too surprised.

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Those stutters and stalls are the main thing that makes a display annoying and not 'live'.  I think a consistent 30fps might be marginally sufficient for most people in most cases just like video, but throw in 5 consecutive missing frames every two seconds and everyone will hate it.

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To record for longer times, I need to reduce the sample rate  (camera).   


--- Quote from: Kosmic on April 30, 2024, 01:17:52 pm ---
--- Quote from: joeqsmith on April 30, 2024, 01:05:10 am ---I placed a stopwatch in front of my scope's display.  Connected to a RF generator set to sweep from 5M - 100M.  Very small data set.  Norm trigger.  All processing turned off.  Camera set to 1000fps.   Recorded for 1sec.  Manually counted each screen update. I measured a pathetic 30fps.  It's an 18 year old PC and based on how poorly it handles the X-Y music, not surprised.

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Not long ago (10 years?), 30fps was pretty standard for most application on a PC. Now these days it has increased to 60 - 120 fps for dynamic and responsive application. Nevertheless, 30fps is still present. For example you still find a lot of video games running at 30fps.

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I wouldn't be surprised if some of the scopes shown in the music thread are running 120Hz.  They are very impressive compared with my scope  running Windows XP.   It's why I had brought up the refresh rate when I asked about buying a new DSO. 

joeqsmith:

--- Quote from: bdunham7 on April 29, 2024, 09:21:50 pm ---I see between 2 and 4 lines on the screen, indicating a 15 to 30Hz screen refresh rate. 

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Now that I can view the file, it appears some are even a single line.   


--- Quote ---What is bit  confusing about the video I posted is that the waveform update is set at 60/s (using line trigger) and the 60fps video shows a display update (pixel change) on each and every frame yet there are multiple traces showing.  This is why I was saying that 'screen rate' or 'screen update' may not be simple, clear-cut concepts.
--- End quote ---

Agree.  It seems that turning off persistence never really turns it off.  I'll try it with mine.

bdunham7:

--- Quote from: joeqsmith on April 30, 2024, 04:38:00 pm ---I wouldn't be surprised if some of the scopes shown in the music thread are running 120Hz.  They are very impressive compared with my scope  running Windows XP.   It's why I had brought up the refresh rate when I asked about buying a new DSO.

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I discovered my phone has a super-slo-mo feature that takes fairly bad video at 960fps.  I don't have time to edit or analyze them right now, but I took two recordings of an 8-level staircase at 10kHz and 1kHz, triggered at 301Hz.  The slo-mo feature apparently produces a video at 30fps with the beginning and end at normal speed and the middle of the video slowed down by 32X (I think).  You can judge the timing yourself by the flashing of the frame of the scope as this is being illuminated by a cheap LED filament bulb that is blinking at 120Hz.

This reminds me of writing video games on very old Z80 and 6502 based computers where the TV adapter would read dual-ported memory at 60 field or 30 frames per second but you couldn't write to the memory nearly that fast unless you had a very simple program.  It looks like that here--you see changes quite often (didn't try to guess the rate yet) but it takes longer to complete them.  The second video, with the staircase at 1kHz, has a nice analog flicker to it in real life and looks quite "live"--no stuttering or stalling at all.

Again, sorry about the .zip format, but YouTube will butcher the video and videos can't be uploaded here.

Edit:  I had a look and it appears that it more or less updates the screen about every two blinks of the lighting, so ~60Hz. 

radiolistener:

--- Quote from: joeqsmith on April 30, 2024, 04:38:00 pm ---Odd, seemed easy enough to detect.  Only problem was manually going through the data.   

--- End quote ---

it will be easy if lcd/led matrix is rated for much higher refresh rate than actually used (very much higher). But usually it is close to actual refresh rate or even worse. In such case you cannot see pixel on/off event immediately, it will be very smooth and it will be hard to determine exact frame when pixel appears or disappears.

If video camera uses lossy compression format, it will be even more hard because compression will remove very small change of pixel brightness between frames.

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