Re: PIC Based VTTC Staccato Controller

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>


 > Hello All,
 >
 > As the subject suggests, I recently tried my hand at building a VTTC
 > Staccato Controller based on the Microchip PIC 16F84 microcontroller.
 > In it's current form, the PIC allows for a highly variable pulse
 > output by selecting one of 3 options, and then varying them up or down
 > (via 3 pushbuttons).  The options are:
 >
 > 1) Change % of AC cycle ON (pulse-width per cycle)
 > 2) Change number of ON-cycles and
 > 3) Change number of OFF-cycles.
 >
 > where by "cycle" I mean the AC cycle at the input to the VTTC.
 >
 > The microcontroller is very nice for reducing the complexity of the
 > board layout and thus easing construction time.  Another possible
 > advantage to the microcontroller approach is the improved noise
 > immunity, I had no problems at all with false triggering etc.  One
 > possible disadvantage, though, is a less intuitive user interface (no
 > knobs to twiddle).  I experimented with using a rotary encoder for
 > this, but it didn't pan out.  This difficulty could possibly be
 > remedied by adding an LCD or 7-segment display, which I plan to do
 > eventually.

Yes, a microcontroller will simplify things greatly and allow much more
flexibility to what you can do with it.  I was thinking of going this way
with my VTTC controller I built, but I had a lot of
problems with using a PIC microcontroller when I was originally using it for
my first SSTC.  The low voltage 5V Vcc for the PIC was getting too much
noise and resetting itself at least when running
the SSTC.  I think there are some PICs which are high voltage PICS capable
of running at up to 12-15V.  I would go that route.

Regarding the bulk order on VTTC Staccato controllers, I still have some
extras if you still wanted one.

LCDs are pretty much useless when operating near your coils, unless they are
powered remotely.  But even then, voltage can build up on any wires leading
to them and disrupt them.  I learned this
the hard way as I was planning on using a variety of LCD panels to provide
voltage and current feedback on my SSTCs.  But when i ran the coils, the
displays just drop out and don't work.

As far as using a rotary encoder, this is actually very simple.  I assume
you want to use this to vary timing delays, pulse widths, etc...  You only
need two inputs for the rotary encoders (A and B) - forget the BCD
mechanical position ones.  For example, when you rotate the encoder, look
for a pulse at output A of the encoder.  Then immediately look at the output
B of the encoder.  Depending whether B is high or low will tell you which
way the encoder was rotated and you can update your timing counter etc...
accordingly.  With a simple program like this, you can using a polling
routine or even an external interrupt (RB0) or Interrupt on Change (RB4-RB7)
if your partcular PIC supports it.

If you ever need help with the PIC, let me know.  I do a lot of consulting
work on the side developing PIC applications.

Good luck!

Dan