I normally work with 5mm or 3mm IR leds and pulse currents between 1A and 2A are quite common. Not too sure about visible light LEDs, I found some that have absolute maximum ratings of 300mA @ 1/10 duty cycle. The used duty cycle for this clock is much lower so I am pretty sure they will withstand at least 500mA. My experience is that is it much easier to fry an LED by applying a too high reverse voltage rather than a too high forward current.
Michel On Feb 2, 1:52 am, jb-electronics <webmas...@jb-electronics.de> wrote: > Are you sure 1A will not hurt your LEDs? It sounds a bit much. > > Jens > > > > > > > > > I have come across another one of these clocks: > >http://www.dougswordclock.com/kits.html > > It looks like he uses 117 LEDs, but maybe he lights up words rather > > than single letters, couldn't really tell. > > > One way of doing it with a single chip is by pulsing the leds for a > > very short time with a very high current (say 1A for 150us), then you > > run through all the leds only turning the ones on that need to be on. > > This way, you cover them all within 20ms, so you can do that 50 times > > per second without a noticeable flicker and it won't matter how many > > are light up at anyone time. The average current through the LED is > > then 7.8mA which is quite good when using high efficiency LEDs. > > > If you go further into that, you can take as a reference not the 128 > > leds in total, but the maximum of leds that are turned on at anyone > > time. Suppose that is like 32 leds or something, you can then go to > > 600us pulses and increase the average current to about 30mA. Of course > > you can only do that if that is still within the specs of the leds. > > > Michel > > > On Feb 1, 6:26 am, Quixotic Nixotic<nixci...@jsdesign.co.uk> wrote: > >> On 31 Jan 2012, at 18:26, Nicholas Stock wrote: > > >>> Gang, I know this isn't nixie related, but I thought I'd bring it > >>> to your attention as we're all clock enthusiasts... > >>>http://www.kickstarter.com/projects/252714519/clockthree-jr > >>> I've built one already and as a Word Clock it's pretty sweet. > >> I think it's doable with a single chip. I have successfully > >> charlieplexed a single chip clock with 144 LEDs and this clock only > >> needs 128. The issue would be how many LEDs are to be lit at any one > >> time, to ensure the refresh rate is flicker-free. I might have to > >> have a go at this after a few other projects have seen daylight. > > >> John S -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
