Digital Timer for Video

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
Thanks for your reply AK.

FPS and shutter speed are two totally different things in video, both important though. The two together are like PWM (freq and duty cycle).
All of my video gear has max 120fps. Thus I should be able to see a digit in successive frames that are near 9msec apart, thus frame-1 is "2" followed by frame-2 of "1", but all I see is "8".

I have a timer app on my android phones, a Honor8 and MotoX android. When video'ing those timers I can see the msec digit moving very fast with my eye, and in the video I can see the msec digit very clearly, and although some time passes between frames each frame of video captures the msec digit, some blurry due to changing, others clear as day. The time seen in each frame does appear to agree with 120fps.

Having this info I believe the segments in these Kingbright displays are simply staying "hot" and are still emitting light even after the current stops for a fraction of a sec. I did contact their tech support to get on/off times for the LED's they use in these displays.

If it's the case that these LED's are just too slow, I can seek out very fast LED's and replace the msec digit with the faster LED's, etc.
 

AnalogKid

Joined Aug 1, 2013
9,353
Thus I should be able to see a digit in successive frames that are near 9msec apart, thus frame-1 is "2" followed by frame-2 of "1"
Not necessarily. The big question is how long the shutter is "open" during the 8.3 ms frame time. My Canon 5D has a mechanical shutter, while my Panasonic (Leica) does not, but both have "shutter" exposure times from sub-milliseconds to seconds. I get that there probably is not a physical shutter in your camera (you have not said the camera type/mfr/model), but the individual pixels are enabled and integrating over a fixed time period during each frame. If that time period is the entire 8.3 ms, then segment e will be illuminated at least 3-4 times in every frame, up to 7-8 times for segment c. Based on everything you've said so far, this is why you see an 8 all the time. This can be confirmed if you post your schematic. If all of the segments have the same apparent brightness, that part of the frame is overexposed.

Back in another life we had an Arriflex 16 mm camera modified for 30 fps for US television work. To adjust the shutter (exposure period, not rate) you had to swap out a metal disc. I remember a lot of cameraman grumbling when lighting conditions changed. The only way to keep an approximately constant depth of focus throughout a shooting day was to change the disc - in the field.

ak
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
Yes, as I mentioned, shutter speed is as important as fps.

Some of the video is done via my android phones, some done using gopro3+, some done using gopro 4k knockoff, all at 120fps. On my phone vids shooting at 120fps I can see msec digits clearly when filming timer app on my phone, so I suspect the shutter is very fast on these. However to note, the screens on these smartphones may actually have delay more than 1msec, so even though the screen is updated with correct info there may be more than 1msec between screen updates, thus the screen is not updating every 1msec, and as such my slow 120fps appears to capture the change. But I also note, the 120fps video does appear to agree with the time shown on the timer app I film. Stepping through frames the time seen sometimes will have math of 60fps, but then on a sequence of three frames the 1st to 3rd shows 120fps and the 2nd frame appears blurry.

I'll try and take a fast pic using my Canon SL1 to see if there is a diff, but I suspect not.
 

MrChips

Joined Oct 2, 2009
24,176
Shutter speed is more important than fps.

If your shutter speed (i.e. the length of time the shutter is open, translated to mean the camera image capture period) is longer than 1/1000 then you will be recording consecutive counter changes. This will result in the likelihood of recording "8" on the millisecond digit. This gets worse at a shutter speed of 1/100 since the millisecond digit would have cycled through all 10 numerals from 0 to 9.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
Well, I use my canon camera to take pic at 1/4000 shutter and I get readable numbers.

It works ;)

My video crud gear is simply not fast enough.

Shutter speed is more important than fps.

If your shutter speed (i.e. the length of time the shutter is open, translated to mean the camera image capture period) is longer than 1/1000 then you will be recording consecutive counter changes. This will result in the likelihood of recording "8" on the millisecond digit. This gets worse at a shutter speed of 1/100 since the millisecond digit would have cycled through all 10 numerals from 0 to 9.
Agreed, need a fast shutter to catch fast item regardless of FPS, but, if the FPS is slower than delta between two events (in this case 1ms between disgits) then the video will show gaps between frames, etc. But also to note, shutter speed cannot be more than fps speed, etc.

Thanks for the feedback. My display will appear with a "8" in ms digit to human eye and slow camera/video stuff. But maybe one day i'll have 1k+ fps (I am still looking for a inexpensive device or diy kit, so if you know of any let me know). 640x480 color or bw 1k FPS I can work use.

Thanks.
 
Last edited:

AnalogKid

Joined Aug 1, 2013
9,353
A work around would be to use a CD4017 Johnson counter as the millisecond digit and display 10 LEDS in a circle.
Maybe not. If the problem is that the image sensor is integrating over several milliseconds, then that system would show an arc of several LEDs. You could count the number of LEDs to determine the actual exposure time, but you still will not get a single LED showing a unique millisecond value.

ak
 

MrChips

Joined Oct 2, 2009
24,176
Why not? The first LED lit tells you when the shutter opened. The last LED lit tells you when the shutter closed.
For a digital camera, it tells you the start and end of the image acquisition. Take either LED or the mid-point of the arc to tell you the exact millisecond of the frame capture.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
Also to note, shutter "open" has a lot of different meaning in world of shutter. Do you start timer when shutter starts to open? Is it "closed" when its fully closed. In other words, when is the shutter actually open? For image sensors exposed to light all the time shutter speed will be fast, limited by sensor materials. Mirrored SLR has mechanics to deal with, and a "curtain", etc.

SLR, no-shutter digital, fps, shutter speeds, etc etc is a huge topic if you are into that arena.

I have had my share of learning some things about my SL1 when making some automation stuff for it. SL1 has horrible lag time between when button is pressed and when actual pic is taken.

Anyways, my timer seems to be working ok. Got 1/100th digit wired in today.
The timer seems to be ok, I just don't have fast enough gear to catch it on the run, etc.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
Surprisingly long times; might be a consequence of the high brightness physics.

ak
Well, I am not sure what their definition of "rise" and "fall" times are. Many times these things are a % from either max or zero current, a term used to describe the conducting phase of the element. I have seen others do it in terms of mcd output.
 

AnalogKid

Joined Aug 1, 2013
9,353
If traditional EE terms apply, the rise time of an LED is the time it takes the output brightness to go from 10% to 90% of its rated output with an infinitely fast input signal.

ak
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
I mounting it in a small "leather" notebook shell (walmart for $4). I added a toggle for run/pause, and upper left has the momentary for reset.
I still thinking about best batt setup. I might use three smaller Li batts instead of std 9v batt. I might add a window to front cover for the display so it can be used closed or open. The toggle will stick through the front cover, it's just a tad too tall, but that's ok, this is no master-chef project ;)

 
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