MOTM

Hello again!

jwbarlow@... wrote:
> 
> Very cool, Frank. Does this device still exist? .... Are these electromagnets > available anywhere?
> 
> JB
> 

Now that I think of it, I think I may still have at least part of the
breadboard we used for this.

I'll try to look over the weekend and see what I can dig up. As I
recall,
other than the chips themselves and the interconnections, there were
very
few other components on the board. Obviously the ULN-2003 was just an
on-off
device, so using a waveform other than a square wave would not work with
this configuration. We never tried any sort of PWM on the signal either.
Since we were really exciting a steel bar, I'm not sure that the use of
something other than a 50/50 square wave would be very helpful, and the
only
change you would notice would be a drop in the amplitude of the ringing
of
the bar as the PW departed from 50/50...?

I used a couple of different electromagnets which were spares from my
stash
of pipe organ stuff. There were smaller magnets which are used to switch
small pneumatic 'circuits', and larger ones which were used to directly
open
channels which supplied pressurized air to the feet of the pipes. The
little
magnets were about 90 0hms to 180 Ohms; the larger ones were from about
60
Ohms to 30 Ohms. A dim recollection I have is that the bigger (lower
resistance) magnets did not always produce dramatically more powerful
results.

I have a few of the smaller (90 Ohm) magnets kicking around, if anyone's
interested in experimenting. No extra spare steel bars that I can think
of,
though...

I have a complete set of steel bars over resonators with rotating vanes
in
them (i.e., a vibraphone) from a pipe organ, and once my pipe organ
project
starts moving, I'll add an all-electric striker action to this... and
now
that I'm thinking about the old experiments, it might be nice to have a
set
of magnets which would excite the bars without them being struck, for an
eternally sustainable vibraphone effect! Hmmm...

Frank