A lot of GPS units will put a 1 pulse per second  out. If you can find the
correct pin. A flip-flop would convert this to 1 second on - one second off
if required or a monostable to required pulse width.. High accuracy as long
as it can see at least one satellite.

RP


On 18 July 2014 18:52, NOPE9 YES <yes@nope9.com> wrote:

>
> On 2014m07d17, at 23:33, Richard R. Pope <mechanic_2@charter.net> wrote:
>
> Hello all,
>     I hope someone can help me with this. I would like to output a
> pulse for one second. This pulse has to be high for one second. It opens
> a gate allowing the frequency to be counted to be applied to the counter
> gates. Then the pulse is pulled low and the counting stops.
>     I want to then output another high pulse of at least 20nS in
> length. I want to be able to adjust the delay from the time that the
> count pulse goes low and when this pulse is output. It would be nice to
> have this pulse occur from say 1 second to never. I.E. the frequency
> count can be updated from once a second to it can be held indefinitely.
>     So for this I would think that a potentiometer being read by an ADC
> could be used to control the update time for counting the frequency. A
> low count would allow the updating to occur very often and a high
> reading would result in no reset pulse being output. I have the picture
> in my head but I just don't know how to translate that into software to
> control the hardware.
>     I was thinking that a pic16f628 would be the choice for doing this.
> Can someone please spend some time with me and help me with this? I have
> hit a wall.
> Thanks,
> rich!
> --
>
> #1  Pulse has to be high for one second plus/minus .... how much precisio=
n ?
> #2  At least 20nS in length .....   is one hour okay ?   20nS to ?????
> #3  Most any micro-processor will do this..... the precision will depend =
on
> the clock driving the micro-processor.
> #4  You can use a potentiometer into an ADC.  I guess you would want to
> translate the incoming voltage into a logarithmic time function such as
>  time delay =3D n**(ADC-voltage * m).  This could be done with a lookup
> table.  Instead of a potentiometer , you could have a pair of buttons ( u=
p
> and down ) .  Or a digital rotary encoder.  I guess the advantage of a po=
t
> is that it will give you some kind of idea visually what the time delay i=
s.
>
> If you are doing only one of these , I would recommend using a developmen=
t
> board to save time and effort.  With more information, various PIClisters
> could give you better advice.  I may have a surplus board I could give yo=
u.
>
> Gus in Denver
>
>
> --
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