On Tue, 30 Oct 2018 18:30:08 -0000 (UTC), Cursitor Doom
<
cu...@notformail.com> wrote:
>On Sun, 28 Oct 2018 21:40:50 -0500, amdx wrote:
>
>> There used to be signs that used movement to get attention, it could
>> be as simple as a waving hand. The hand was setup as a pendulum and when
>> the battery was installed you could give it a push, this would close a
>> switch, energizing the solenoid and giving the pendulum a kick this
>> would also open the switch. The pendulum would go through its swing and
>> then come back and close the switch, repeating the cycle.
>
>Sounds grossly inefficient. I'm reminded of those Chinese cat things with
>the waving paw. They seem to have got battery life down to a fine art;
>must be using a 'joule thief' or some variant thereof I would imagine.
The so-called joule thief is what was called a blocking oscillator
back in the days of vacuum tubes and you could find one in every tube
type TV. The flyback pulse produces a high voltage because the
tube/transistor is cut off abruptly, and the collapsing field produces
a voltage spike.
Those moving display gizmos were neat, I used to play with them as a
kid. A single D battery or pair of them could keep the thing swinging
for a week or two. The magnet was on a half-circle of wire and
suspended so it would pass through the coil, working a leaf-switch of
a couple of phosphor bronze springs that would repel the magnet as it
passed the midpoint. What is impressive was the length of time they's
keep working - particularly with the zinc carbon batteries we had in
those days.
Transistors cost money back then too. My first blocking oscillator
using transistors was pulled from a Radio Electronics magazine for a
"sonic shake table" (an interesting gizmo that could make standing
waves in particles of flour in an upturned speaker cone - or mercury
if you happen to have some) When I got tired of playing with it, I
added it to my bicycle for a horn and ran it off the hub mounted
alternator.