[time-nuts] Frequency divider design critique request
bruce.griffiths at xtra.co.nz
Wed Jul 16 17:27:16 EDT 2008
David C. Partridge wrote:
> I'm waiting to see what Magnus Danielson has to say, as it was he after all
> who suggested adding caps in parallel to the pull-downs, and also series
> Thinking about it retrospect, I think he may have meant the series resistors
> to go between the pull-downs and the chip, rather than where the schematic
> fragment showed them.
> I don't *think* switch bounce is an issue here, as it will all settle to the
> right answer pretty sharply.
> Magnus, are you there?
Switch bounce could be an issue if one wished to switch cleanly to
another frequency output without incurring extraneous transitions during
the changeover from one frequency to another.
A hex D(74HC174) or an octal D(74HC374 74HC574) could be used to
synchronise debounced multiplexer select inputs.
Another issue is that all BCD switch contacts will not make or break at
the same time.
Also the debounce filters will not all settle simultaneously.
Thus a debounced enable pushbutton may also be required.
When the enable pushbutton is depressed the current state of the
selector switches is latched.
In this case only the enable pushbutton need be debounced.
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