Basic Stamp Controlled Spark Gap

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

Original poster: "Jeremy Scott by way of Terry Fritz <teslalist-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>

Hi,

I'm designing a basic stamp controlled rotary spark
gap that will be able to decide for itself the
optimal timing for gap electrode presentations.

Mechanics:

The gap will have 1/4" tungsten electrodes, either
four or eight of them depending on what it's capable
of spinning.

The following will be controlled or read by the stamp:
(Feel free to comment if you know of a better way!)

Tachometer feed back - 1/4" a hole in the disc will
break the beam of IR light and drive a phototransistor
hooked up to an input pin. This will create a stream
of pulses that can be measured. RPM and electrode face
time will be calculated in the stamp. The hole will
be some fixed number of degrees away from an
electrode, the basic stamp will use this (along with
RPM) to calculate exactly 'when' a rotating electrode
passes
a fixed point.

Speed control -  H-Bridge push/pull type circuit
using power MOSFETS and an output from the stamp.
This and the tachometer feedback will keep the
motor running at a consistent speed by varying
the frequency of AC. This should compensate for
any desyncronizing drag of the disc. How fast
it rotates is yet to be determined. Initially
planning on 1800RPM with eight electrodes for
up to 240BPS.

Phase control - R/C type servos will rotate the
'fixed'
pair of electrodes (connections to the power supply)
anywhere from 0 to 90 degrees in fractional degree
increments.

Timing signal -- this is the hard part, it involves
two things: a) figuring out where in the capacitor's
charge cycle the spark gap is firing, and b)
quantifiying the capacitor voltage when this happens.

I believe this has to be done with an analog to
digital converter which constantly 'reads' a rectified
voltage from the capacitor. (Also the voltage across
the secondary windings of power transformer)

The voltage has to be scaled down and isolated, which
is the tricky part. Most likely I'll devise some kind
of voltage controlled oscillator which will send a
modulated tone over a beam of 38Khz IR light. Basic
stamp should be able to convert the tone (pulses) into
a digital value. The gap can then be adjusted such
that the maximum value is read from the capacitor just
before electrode presentation.