Afraid I'm not all that good on Analog or RF (It's just been too
long), Erik;  Some thoughts to get the list shooting me down here <G>

  I quote from Richard Martin's post of April 7th:
> The NE602 part (and it's 'kin) is usually used in RF circuits
> but it includes (in part) a 'Gilbert Cell Multiplier' which
> is (over SOME range of inputs) an analog multiplier with
> fairly good specs (and cheap, since NE602s are ~$2.00).
> <snipped>
> Thanks:  <Probably should reply to ME ONLY rmmartin@serv.net>

  Philips Semiconductors makes this part (aka SA602A), Questlink.com has
data on it as well, for a .pdf file hit
http://www-us2.semiconductors.philips.com/acrobat/datasheets/SA602A.pdf.

  Works to 200MHz from a quick glance.  Sounds like a place to look.
And a person to ask <G>  DIL-8 or SOIC-8 package.  You may have to go to
a powers of 2 style multiplication, i.e. multiply Sin(a) * Cos(a) to get
output == Sin(a*2);  I'm not sure offhand, this AM, how to get Sin(a*5)
with trig. identities, but I'm sure you can do 3 2x multiplies in a row,
to get 8x, that should do you?  Maybe you can figure a way to do 5x,
though, as odd multiples are so easy to get from square waves! <G>

  Another thing to think of is PLL's, and how radio IF's and so on
work;  NE564's work up to 50 MHz, could you mix an oscillator output
just below your LOWEST desired frequency with the PIC output & then high
pass & feed the upper component of that into a PLL to give you a nice
clean output?  Or "Kick" the PLL at the right time each pass through the
output wave, to sync it up with you?  (Schmidt or comparator the output
of the PLL, as needed to give you your 50% result.  A comparator with 1
input direct to a sine wave source & the other input on that same
signal, low pass filtered through a RC filter, can do a good job of
making your sine wave become a 50% duty cycle square wave;  Throw a
couple 1N4148's in there across the R, to pull the cap up to about 50%
faster, if needed.)

  Would lookup tables / Magic Sines be one possibility here?  (Fed into
a PLL perhaps.)  Probably not, sounds like.  Also royalties may be a
hardship there?

  (I'm hoping someone who's better on RF/Analog helps you here <G>)

  Mark

erik wrote:
>
> Hello all.
>
> I'm working on a project where I'm simulating a machine that we are
> collecting a bunch of data from.
>
> The little gadget would have to be configurable via switches to output a
> 50% duty cycle pulse at various
> frequencies.
> The maximum frequency would be about 71kHz. That means that I must
> evaluate the configuration switches,
> check a timer/counter, and turn on an output, plus execute the rest of
> the program in about 72 instructions.
> (that's if there are no jumps or gotos)
>
> It's becoming pretty clear that I just won't be able to do it.
>
> This output is to simulate an encoder and all other outputs must be "in
> tune" with this encoder (machine speed) This requirment would seem to
> rule out using 1 microcontroller for the encoder signals and another for
> the rest.
>
> So, If I was to give an output pulse at say, 1/10th of the desired
> frequency, is there a frequency multiplier of some sort that I could use
> for an application like this? I'd like the PIC to output a 7.1kHz pulse,
> and do a bunch of other neat stuff, and use another IC or circuit to
> multiply the 7.1kHz signal by 10.
>
> Erik