After my post, I gave it some thought.
My criteria still are:
*pocket sized
*battery operated
*direct display of BPS
*works with vacuum tube, solid state, as well as spark gap coils
*cheap and simple
I'll add:
*range from 100 to 1000 BPS
*accuracy of +/- 5%
I thought, as you did, that light from the gap might be a viable
measurement point. But it would be difficult to get down near a gap on a running
coil, and if you were too far from the gap you'd likely get interference from
reflections and the secondary arcs.
Besides, that wouldn't work on a vacuum tube or solid state coil.
I figured the antenna method might be the most reliable. I drew up a
very simple input end, which on further research turns out to be the standard AM
detector circuit (no surprise!). This should turn the decaying sinusoid
output into a pulse train.
From there, I figured one could run it directly into a digital
tachometer panel meter. But those things go for $50+ new, and I don't have a spare
sitting around. I looked at the digital photo tachs the model airplane hobbyists
use for tuning engines. They run around $20. Maybe it would be easy to hack
one (and even use for the basic project box!). Heck, they might even work
as-is if you just point it at the gap.
Or you could run the pulse train into a Freq-to-voltage converter chip,
and drive an analog meter (but tough to keep 5% accuracy at the low end of
the scale. Maybe not so important, as the 10x range would be handy enough?
Or run the pulse train through the usual manipulations, and drive a
3-digit LED 7-segment display. Still cheap and simple, but tedious for me. I'm
sure there's somebody here who would get some satisfaction from designing the
simplest way to implement this. I was hoping Mr. Piranha would, since this
would be right up his alley, and "Terry Tach" has a nice ring to it. ;)
Wouldn't it be great to pull out a little gizmo at a Teslathon, and
start comparing each other's breakrates? Yeah, it doesn't get geekier than that,
but it would probably reveal a lot and allow for meaningful discussion
without the usual speculation and hand-waving.
-Phil LaBudde
(yes, I own several oscilloscopes, but I'm lazy)
Center for the Advanced Study of Ballistic Improbabilities
**************Ideas to please picky eaters. Watch video on AOL Living.
(http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/
2050827?NCID=aolcmp00300000002598)
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