On Mon, 9 Dec 1996, Octavio Nogueira wrote:

>  At 10:54 AM 12/9/96 -0600, you wrote:
>  > You must be careful subbing 74 series parts here for CMOS.  This device
>  >is powered
>  >by stealing power from the Printer Port by using data output lines to
>  >charge a cap.  Therefore VCC will never be a true 5 volts.  Depending on
>  >the PC, this stolen VCC will always be less than
>  >5 volts, it could fall as low as 3 volts on some PCs.  That is the reason
>  >the author/designer
>  >chose to use CMOS devices, because they can function on this lower
>  >voltage.  74HC parts require a good solid 5 volts.
>
> > I haven't checked my data book yet, but I thought the 74HC parts were
> CMOS
> > and could handle the lower Vcc.  The other 74 series may be a problem
> (i.e
> > Plain, LS, etc.).  I plan to add a power supply for the 5VDC anyway.  I'm
> > not a big fan of stealing power from the port.


74HC(U) should work from 2 - 6 V
74HCT should work from 4.5 - 5.5 V

bernhard.

> >
> > Norm
>
> I don't think you need to use 74HC parts, Digi-Key have the 40XX parts
> needed
> in the project.
>
> Octavio
> ========================================================
> Octavio Nogueira
> e-mail:   nogueira@mandic.com.br
> homepage: http://ourworld.compuserve.com/homepages/tato
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>

Bernhard Schweighofer alias schweigi@sbox.tu-graz.ac.at
(Student at Graz University of Technology, Austria)