piclist 1998\11\03\125414a >
Thread: chronometer
picon face BY : Peter L. Peres email (remove spam text)

On Mon, 2 Nov 1998, Lucuix Christian wrote:

> First of all, I want to thanks all of you for the replies.
> I'm a bit confused, because my question was not so precise.
> For the display I'm using a Futaba 2x20 characters fluorescent display
> because of the working conditions (deep dark under the sky), the user have
> a 12 keys keyboard to interact with the chronometer, and I'm using a PIC
> 16C84 to control it.

A futaba display needs a high voltage driver. Maybe using a backlit LCD or
LEDs is better ?

> The idea is to measure the time between two events (CCD camera shutter
> open/closure), so an absolute precision is not needed ( only differential
> measure) . What is important is to have a drift as low as possible for a
> duration of half an hour.

So you can live with a 5 ppm timebase ;) If you stick a normal crystal in
a small oven and calibrate it it will do that. This means that you can use
a PIC ;)

> I first planed to use the PIC himself to implement the chronometer (all
> software approach) but the user can interact with the chronometer during
> the measurement to act whit the instrumentation, so an all software
> approach is not usable. That's why I'm looking for a chip, which is able to

Why not ? There are interrupts, constant run-time segments and other ways
to do it all in software.

> handle the time. If this pretty all done chip is not yet on the earth
> (sic), I'm going to realize the timer with discrete circuits (re-sic)

Aiee ;) Actually, for a 5 ppm timebase you should concentrate on as FEW
components as possible, at least in the oscillator. Otherwise behavior
over temperature will require a doctorate thesis to be compensated
somewhat imho.

> For Peter L. Peres, the Pic du Midi observatory is in the Pyrenees, but
> congratulation for your analyze (the top of the mountain is a very colder,
> higher, and E.M.C disturbed place, ha ha ha).
> Christian.

Ok I did not get my geo.



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