TTL hex buffers won't help you, they have the same voltage thresholds
as the PIC inputs.

I used TI's TLC3704 comparator in a recent analog-PWM design. It's a cheap quad
comparator that's worked well for me.

Regards,
Mark
markrages@gmail

On Fri, 3 Dec 2004 13:16:14 -0000, Mcgee, Mark <mark.mcgee@csfb.com> wrote:
> Hi.
> 
> One of the five lines I need to convert is a data clock, but it's about 1kHz,
> so hopefully, this won't be a problem.
> 
> I'll check out the hex buffers though, thanks for the suggestion
> 
> Regards,
> Mark
> 
> 
> 
> > -----Original Message-----
> > From: piclist-bounces@mit.edu
> > [mailto:piclist-bounces@mit.edu]On Behalf
> > Of Jake Anderson
> > Sent: 03 December 2004 13:07
> > To: Microcontroller discussion list - Public.
> > Subject: RE: [EE]Darlingon array, was Will this voltage
> > shifter work for
> > m y application?
> >
> >
> > just a caution and a suggestion to boot
> > if you are trying to send high speed data you will want a
> > fairly "strong"
> > pull up depending on signal length.
> >
> > capacitive and inductive effects mean that it may take the
> > line a while to
> > rise from a low to a high.
> > I had a similar problem with a level converter.
> > I was running from 3.3v to 5V SPI, over about 20cm of cord
> > (the cord had the
> > 5v signal on it), I just used a TTL hex buffer.
> > its high threshold was around 2 and a bit volts and the
> > dataflash had a
> > minimum output of 3
> >
> > other upside is 6 converters in one chip ;->
> >
> > I was running that at ~62KHZ I think
> > 20mhz 16F877 at fosc/64 SPI
> > resistor divider down converter and the buffer back up.
> >
> >
> > > -----Original Message-----
> > > From: piclist-bounces@mit.edu
> > [mailto:piclist-bounces@mit.edu]On Behalf
> > > Of Russell McMahon
> > > Sent: Friday, December 03, 2004 23:06
> > > To: Microcontroller discussion list - Public.
> > > Subject: Re: [EE]Darlingon array, was Will this voltage
> > shifter work for
> > > m y application?
> > >
> > >
> > > > Thinking about the OpAmp solution, wouldn't a comparator be even
> > > > better/more
> > > > suited to my application?
> > > > LM339 quad would do the trick, (or rather a pair of them
> > - I need 5
> > > > comparators - bugger!)
> > > >
> > > > I assume the LM339 can switch at 1kHz comfortably?
> > >
> > > LM339 is a technically superior solution BUT, unlike the L:M324
> > > which drives
> > > high actively, all its comparators are "open collector"
> > output so need a
> > > pullup resistor. using Dave Minklers suggestion of using pullups
> > > on the PIC
> > > you could do it with no external pullups.
> > >
> > > > You mention a decoupling capacitor on the supply.  I am using
> > > an LM317LZ
> > > > vreg
> > > > to provide regulated 5v, from a 12v DC input (& another for
> > > 1.5v) for PIC
> > > > and
> > > > possibly now the LM339, which has a 0.1uF(IIRC) capacitor
> > on the output
> > > > already - so will I still need a further decoupling capacitor
> > > for the IC?
> > >
> > > A 0.1 uF for each IC between its power supply pins is usually a
> > > good idea.
> > > Not always essential - but it's a shame to have things fail due
> > > to excessive
> > > noise for want of a cap worth a few cents.
> > >
> > >
> > >         RM
> > >
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