Accurate Timebase
Archiver
Posts: 46,084
Hello again...
I need to make an accurate timebase of 1khz to increment a 47ls90
counter.
I have tried with 555 timers (both TLC and CMOS using temp comp
resistors, astable mode, 66% duty cycle) but found that the freq out
varies to much, up to 5% due to differences in temperature.
I have also played with 14 stage counters & 32.768 khz crystals, but
I can only get a 1024 hz division. Even though this is better then
555, the error is still 2.4%
The max error is 0.5-1% max that I want to achieve.
I am using this output to drive 6 cascaded 4790 counters to provide a
six digit time output from minutes to thou of a second. The counters
are being shifted into the stamp by cascaded shift registers.
What I am trying to achieve is to measure time periods from minutes
to thous of second with tenths of a second accuracy. If anyone has a
better way of doing this then please let me know.
I have tried using a pcf8583 i2c ic for this job but could not get it
to interface with my bs2.
Any help or suggestions, circuits and code would be great.
Thanks again,
Simon
I need to make an accurate timebase of 1khz to increment a 47ls90
counter.
I have tried with 555 timers (both TLC and CMOS using temp comp
resistors, astable mode, 66% duty cycle) but found that the freq out
varies to much, up to 5% due to differences in temperature.
I have also played with 14 stage counters & 32.768 khz crystals, but
I can only get a 1024 hz division. Even though this is better then
555, the error is still 2.4%
The max error is 0.5-1% max that I want to achieve.
I am using this output to drive 6 cascaded 4790 counters to provide a
six digit time output from minutes to thou of a second. The counters
are being shifted into the stamp by cascaded shift registers.
What I am trying to achieve is to measure time periods from minutes
to thous of second with tenths of a second accuracy. If anyone has a
better way of doing this then please let me know.
I have tried using a pcf8583 i2c ic for this job but could not get it
to interface with my bs2.
Any help or suggestions, circuits and code would be great.
Thanks again,
Simon
Comments
easy to do by resetting your counter at the count of 33 with AND or NAND
gates.
Ray McArthur
Original Message
From: <egroups@d...>
To: <basicstamps@egroups.com>
Sent: Tuesday, October 31, 2000 8:21 AM
Subject: [noparse][[/noparse]basicstamps] Accurate Timebase
> I need to make an accurate timebase of 1khz to increment a 47ls90
> counter.
>
> I have tried with 555 timers (both TLC and CMOS using temp comp
> resistors, astable mode, 66% duty cycle) but found that the freq out
> varies to much, up to 5% due to differences in temperature.
>
> I have also played with 14 stage counters & 32.768 khz crystals, but
> I can only get a 1024 hz division. Even though this is better then
> 555, the error is still 2.4%
>
> The max error is 0.5-1% max that I want to achieve.
>Hello again...
>
>I need to make an accurate timebase of 1khz to increment a 47ls90
>counter.
I recently bought the NX-1000 Universal Training Board for the StampII/IISX
from
Parallax. (Great product!) It is made by a company called INEX. Among the
goodies on the board is an 8 pin dip pulse generator that outputs 1, 10, 100,
and 1000 hertz selectable at at the press of a button. The chip appears to be
also made by INEX (Innovative Experiment, btw) and is their part number PGX4100.
>Reply-To: basicstamps@egroups.com
>To: <basicstamps@egroups.com>
>Subject: Re: [noparse][[/noparse]basicstamps] Accurate Timebase
>Date: Tue, 31 Oct 2000 15:39:34 -0500
>
>If you divide 32,768 by 33, you get ~993 Hz which is within 0.7%. It is
>easy to do by resetting your counter at the count of 33 with AND or NAND
>gates.
>
>Ray McArthur
>
>
Original Message
>From: <egroups@d...>
>To: <basicstamps@egroups.com>
>Sent: Tuesday, October 31, 2000 8:21 AM
>Subject: [noparse][[/noparse]basicstamps] Accurate Timebase
>
> > I need to make an accurate timebase of 1khz to increment a 47ls90
> > counter.
> >
> > I have tried with 555 timers (both TLC and CMOS using temp comp
> > resistors, astable mode, 66% duty cycle) but found that the freq out
> > varies to much, up to 5% due to differences in temperature.
> >
> > I have also played with 14 stage counters & 32.768 khz crystals, but
> > I can only get a 1024 hz division. Even though this is better then
> > 555, the error is still 2.4%
> >
> > The max error is 0.5-1% max that I want to achieve.
>
>
>
>how about a 1mhz crystal driven by a 4049 hex inverter and divided by three
>4017 counters set a 10 that would give you the signal you are looking for.
>
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PIC.
The result is a precision clock PIC which provides clocks ranging
from 1 ms to 1 hour. The timebase is a 4.096 MHz crystal which
should provide 0.01 percent accuracy.
See http://www.phanderson.com/clock.html
Peter H Anderson, pha(at)phanderson.com, http://www.phanderson.com
Homebrew BS2, BS2 Starter Packages