Re: How good a "sine" wave to drive a selsyn/synchro?


"jtaylor" <jtaylor@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:maW_e.17153$p5.6018@xxxxxxxxxxxxxxx!nnrp1.uunet.ca...
>
> "Genome" <ilike_spam@xxxxxxxxxxx> wrote in message
> news:p6W_e.4061$9l4.3584@xxxxxxxxxxxxxxxxxxxxxxx
> >
> > "jtaylor" <jtaylor@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> > news:OuR_e.13362$p5.1689@xxxxxxxxxxxxxxx!nnrp1.uunet.ca...
> > > The simplest way to get this pair of devices working in a non-400hz
> > 3-phase
> > > environment seems to be to program a pic to generate three-phase and
> > amplify
> > > the output. If I have three pins per phase and run each through a
> > resistor
> > > of some calculated value I can make a psuedo-sinewave. Is this likely
> to
> > > have any issues because it's not a true sinewave? This is a
hobby-level
> > > application, so good enough will be good enough....
> > >
> > >
> >
> > If you have three pins per phase then you have nine pins. If you make a
> > johnson counter for 6 of the pins and take a weighted sum through the
> > resistors then use the seventh bit for polarity then you get something
or
> > another with two bits to spare. To get your three phases you offset the
> > summing resistors for each phase.
> >
>
> This sounds good but it's a bit over my head - how will I get the three
> phases to vary at 120 degrees?
>
>

Have a look at the bit about LFO generation using a ring counter at....

http://www.geofex.com/Article_Folders/LFOs/psuedorandom.htm

There is also a circuit in H&H, the art of electronics. I think you scale
the resistors as some Sin(X)/X function but I can't remember.

Use six of your pins on the pic to implement the walking ring counter and
then add the summing resistors like this (arbitrary values chosen)

Phase 1) Phase 2) Phase 3)
10K 15K 20K
15K 10K 20K
20K 10K 15K
20K 15K 10K
15K 20K 10K
10K 20K 15K

So each set of resistors is shifted two bits compared to the previous one.

DNA


.

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