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Nixi Tube vs. LED latency
noreply:
I recently have seen a video on the characterization of a nixi tube – where its ‘on’ and ‘off’ latency was measured with a high speed video camera (we are talking about camera capable of 1M frames / sec)
It was interesting to see this – because a visual source (the camera) was used instead of some electronic test equipment (ok – you could say the camera is a form of electronic test equipment)
When the nixi tube was ‘warmed-up’ – the ‘on’ latency was extremely low – you could switch the ‘on’ at 100KHz with no problem
The ‘off’ latency was much longer – however this was caused by the ‘decay’ of the emission of photons – once the charge (voltage) was removed from the digit in question. It still persisted – but the ‘on’ of another digit will drown out any persistency – so in effect the ‘nixi’ could be driven at the ‘on’ latency alone – at least 100KHz
The background for the above test with nixi tubes – was to develop a ‘digital’ clock – accurate to at least 1/100,000 of a second – to calibrate high speed cameras.
In essence – the camera ‘films’ the digits of the clock (the nixi tubes in this case) – which appear to be ‘on’ continuously (at least the digits representing < 1/10 sec) – but in reality are being switched at 100KHz – so we can resolve 1/100,000 of a second.
The project was very interesting and proved to succeed in what it set out to do.
In hindsight (other than the beautiful ascetics of the nixi tube) – purely from the test results – why nixi tubes and not , say 7 segment LED’s?
This made me think about the latency of a LED (typical) and it is much lower than the 100KHz of the nixi – so is there something , not so obvious, that prevented LED display from being used instead of the nixi??
Has anyone ‘clocked’ an LED 7 segment at > 100KHz – and checked if all segments are illuminated at the clock cycle (not sure how you would do this without a high speed camera – unless you use some photodiodes at ‘each’ of the 7 segments of the display)
So, some questions for discussion ...
How can we 'test' latency of 7 segment LED display using , say, oscilloscope and AWG ??
How could you test the 'on' and 'off' latency of a nixi tube - electronically (using oscilloscope and AWG)- rather than a high speed video camera??
Any feedback or comments would be appreciated ;)
NiHaoMike:
A lot of LED displays are multiplexed. But I don't see why you couldn't use one that isn't.
schmitt trigger:
It would be very interesting to build a fast photodiode preamp, where one could shine the light from an LED being clocked at successively higher rates.
I can tell you though, that many years ago I attempted to build a stroboscope with some Luxeon 3W white LEDs. The phosphor latency rendered them unusable for such task above 100 Hz approximately.
This is a photo of bouncing marble at a rate of 50 Hz, and one can already see a little motion blur.
rdl:
NASA used LED displays in some of their cameras filming the Space Shuttle. You can see them in this video. At some point they explain what the numbers represent (I think, been a while since I watched it). The video has some great views of the shuttle during launch.
noreply:
--- Quote from: schmitt trigger on June 18, 2020, 02:19:57 pm ---The phosphor latency rendered them unusable for such task above 100 Hz approximately.
--- End quote ---
Yeah ... precisely
I suspect that despite an LED having a very low latency (the diode 'on' time) - when it comes to the actual 'visible light' - there might be other issues especially when dealing with optoelectronic devices - like you mentioned :-\
The NASA video - and the 'LED' time stamping in the camera - falls short of the 100KHz - but perhaps they did not need this (100KHz) resolution??
There might be 'more than meets the eye' as to why nixi tubes were used for the clock - looking at it from a purely electronic point of view - not withstanding that the guy who made the clock also hand makes the nixi tubes as a business.
Below is the link to the video which inspired me to make this post, as it raised some interesting questions – which were not covered in the video ...
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