Subject: Re: 555 Clock Circuit
Date: Sun, 15 Sep 2002 12:28:02 +0200
Organization: Wanadoo, l'internet avec France Telecom
NNTP-Posting-Date: 15 Sep 2002 10:28:03 GMT
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> James wrote:
> > Hi all,
> > I'm very new to electronics, and just wanted to start with something
> > small. I was thinking of constructing a binary clock, and have drawn out
> > my design. I was just wondering what to use for the impulse to my 4-bit
> > binary counters. I was thinking of using a 555 IC set to 1hz. Is it
> > possible to create a clock with the 555 IC, or will it never be accurate
> > enough with my cheap materials to produce an Impulse that doesn't lose
> > time? Is there any other device that I could use? If it is possible, I
> > would like to use the 555, as I already have those on hand and available.
> > Thanks for any help in advance,
> > James
> It depends on the accuracy you need and your learning objectives. You won't
> acheive the "real clock" frequency stability without a quartz crystal. A
> straightforward way would be to use a CD4060 type of IC
> (http://us.st.com/stonline/books/pdf/docs/2055.pdf ) which incorporates the
> oscillator circuit and a divisor; this is very simple. Note however that if
> you were using the most popular 32.768kHz crystals, it would provide 2Hz and
> you would need to add another stage of division by 2.
> Then if you want to learn the analog electronics, we could look at some
> discrete quartz oscillators.
Oh, and there is also HCF4521
(http://us.st.com/stonline/books/pdf/docs/2084.pdf) which profides the
outputs F/2^18 to F/2^24 - using this to get 1Hz would imply using a different
crystal, e.g. 4,194304 MHz
(but one needs to pay attention to the max working frequency vs. Vpp).