10 Jul
2007
10 Jul
'07
8:25 a.m.
It's an oscillator built around a capacitor and
something with a
breakdown voltage, a neon lamp for example.
With a breakdown voltage, a (lower) extinction voltage, and such that
breakdown does not harm it (in contrast to, say, a reverse-biased
silicon diode, which would likely fry in such a circuit).
The capacitor charges slowly through a resistor at a
calculable rate,
and then (partially) discharges through the neon lamp quickly when
its ionization threshold is reached and it conducts...then the cycle
repeats. You vary the frequency of oscillation by changing the value
of the charging resistor.
But you get only tiny on times. Add another resistor and use a larger
cap and you can stretch the on time - indeed, with a bit of care you
should be able to get pretty much any duty cycle and frequency.
What's neat about it is that the blinking light is
actually an active
part of the oscillator, rather than just an indicator that displays
the oscillator's state.
Indeed. The hysteresis in the voltage/current characteristic of neon
bulbs lends itself to lots of cool hacks.
/~\ The ASCII der Mouse
\ / Ribbon Campaign
X Against HTML mouse at rodents.montreal.qc.ca
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B