On 9/20/2012 10:37 AM, Jeff Thomas wrote:
On Wednesday, September 19, 2012 6:39:22 PM UTC-7, dr pepper wrote:
So why is multiplexing a bad idea, and static displays make tubes last
longer?, does multiplexing accelerate cathode poisoning or something?
I have 3 or 4 prototypes I've put together and they all use
multiplxing, even the single tube ones use pwm as a brightness control
(and so probably inherit the 'bad habits' too).
Pro's: Reduced component count.
Cons: Significantly reduced brightness in comparison to direct drive at
equal cathode current. Visible flicker- like POV, accentuated at periphery
of vision. Audible noise, or buzzing.
Flickering is not an issue if the refresh rate is high enough. The audible noise
is subject to the tube itself, so it may or may not be present. The clocks that
I built had neither of these problems. And I set the display brightness to that
which would result in the same tube lifetime as a direct drive display, which is
about twice the direct drive current for a 1/6 duty cycle display.
The main disadvantage of a multiplexed display is that you have to worry about
those details, and other details such as ghosting of adjacent digits. So it's a
technique best used by more advanced clock builders willing to take the time to
learn about and solve the problems that may crop up.
--
David Forbes, Tucson, AZ
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