[time-nuts] Atomic Clocks: It is important that they keep good time, Part 1

[Bob Bownes]

Add a tiny speaker so you can simulate the loud 'tick' of the analog clock.
;)

On Fri, Jan 4, 2019 at 4:29 PM ed breya <eb at telight.com> wrote:

> Paul, what do you mean by the display "looking pretty ratty?" As I
> recall, the original buck regulator had regulated output voltage around
> 5V for the LEDs. and the PMOS clock IC needed something around 12V.
> Whatever the LEDs run from, it should be regulated and well filtered. If
> the LEDs are dim, it could be the old displays themselves are
> deteriorated, or the regulation isn't right, or maybe a bad output
> filter cap on the buck converter. If the brightness is OK, but digit or
> segment intensities fluctuate with count, then it's probably a
> regulation issue.
>
> I used the shunt regulator to isolate the rest of the system from the
> large variation (about 3:1) in total LED current with readout values,
> and it was possible because I had made lower supplies anyway, via DC-DC
> converters. You wouldn't want to linear-regulate all the way down from
> the main supply around 24V, to a few V for the LEDs. As I recall, the
> peak load is in the 200-300 mA range at good brightness. The efficiency
> of the buck converter makes it practical to run this from the normal
> supply or battery voltage. I think the original deal was that on power
> failure it switched to battery mode, the buck converter was shut off to
> shed the LED load, and the clock IC stayed powered up to keep the right
> time. The button below the display could force it to show when needed.
> Mine will work the same way, when/if I ever finish all the details, but
> will have adjustable brightness, and maybe the option of still
> indicating time in backup mode, with very dim LED setting.
>
> Ed
>
>
>
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