10 Jul
2007
10 Jul
'07
2:02 p.m.
On 7/10/07, Dave McGuire <mcguire at neurotica.com> wrote:
> Relaxation oscillator?
It's an oscillator built around a capacitor and
something with a
breakdown voltage, a neon lamp for example. 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.
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.
When I was a kid, my dad had a blinkenlights box on the bookshelf he
built in college (somewhere between about 1958 and 1964) - it was a
bakelite box, about 6"x9"x3", with a 3x3 grid of neon bulbs sticking
out the front, and some flying-lead-mounted components on the inside,
I presume nine caps and nine resistors, all of varying values, and an
old snap-end radio battery (B battery?) You snapped a battery in,
then the lights would blink in a random and pleasing fashion.
I doubt he still has the box (I last remember it in the mid-1970s),
but I wouldn't know where you could find a battery these days that
could light a neon bulb - unless you wanted to gang a bunch of 9V
batteries together, or make run a DC-DC converter off of some smaller
value.
Not a complicated circuit, but fascinating to a 7 year old.
-ethan