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