> >> Jason White wrote:
> >> Hello All. I'm currently working on a project that requires me to use
> >> 2 1:16 multiplexers to interface with various peripherals due to
> >> limited I/O. I'm curious how much (RC?) filtering would be required to
> >> make a short fast pulse (eg. 1-10khz 1-5% duty cycle) a suitable
> >> signal to drive a relay.
> >> Thanks
> >>
> >> relay: odd Chinese 20A H-Bridge relay on hooked up via opto-coupler, N=
o
> >> other specs multiplexers: CD74HC4067M MCU - 16f690
> >
> > Just a suggestion, you might get a lower part count/space/cost solution=
 if
> > you
> > instead look at cascaded serial shift registers (74HC165, 74HC595 etc) =
for
> > output
> > expansion. Then you won't need R,C & possibly no FET either. I'm sure
> > there are
> > examples at piclist.com but I can't find any right now.
>=20
> I agree. There are parts that Allegro used to make (6832 and similar) tha=
t
> have a serial in, parallel out shift register plus a parallel latch plus
> high current drivers. You shift the data out, latch it, and the output
> fets are updated. TI makes similar 8 bit parts, but I can't find the part
> number right now.

Yes, I use TI's TPIC6A595. Serial operation as per standard 74xx595, eight =
low side=20
MOSFET outputs, 350mA each with short circuit protection and voltage clamp.=
... so=20
you can get away with no diodes across your relays.

--=20
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brown@clear.net.nz


--=20
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