Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!att!cbnewsc!psfales
From: psfales@cbnewsc.ATT.COM (Peter Fales)
Newsgroups: sci.electronics
Subject: Re: 555 IC Timer help needed
Message-ID: <3481@cbnewsc.ATT.COM>
Date: 26 Sep 89 17:19:20 GMT
References: <169@uwm.edu> <568@limbic.UUCP>
Organization: AT&T Bell Laboratories
Lines: 53

In article <568@limbic.UUCP>, gil@limbic.UUCP (Gil Kloepfer Jr.) writes:
> In article <169@uwm.edu> duc@csd4.csd.uwm.edu (Duc Minh Tran) writes:
> >
> >                        Vcc
> >                         |__________
> >                         |          |
> >                         /        __|__
> >  R = resistor         (R1)    __|_____|__
> >  C = capacitor          \____|  4     8  |  
> >                         |    |7          | (Output)     __    __
> >                         /    |          3|---------> __|  |__|  |__
> >                       (R2)   |   (555)   |
> >                         \____|   TIMER   |
> >                         | +  |2          |
> >                         | |__|           |
> >                         |    |6    1    5|---> ???
> >                        -+-   |_____+_____|
> >                       (C1)       __|__

> Also note that, although I don't see it in this data sheet, that in all
> other places I've read it is unwise to make R1 any smaller than 1K ohm.  I
> may be wrong about this, but I thought I read it somewhere.  It's probably
> a good rule of thumb.

The reason for this is that during the discharge portion of the cycle
pin 7 is connected directly to ground.  You have 5 volts on one end
of R1 and ground on the other.

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-- 
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