and ID is 0.940”, making the wall 0.03” thick.
Each tube has a metal plug and a plastic loop in
one end from which it hangs. The solenoids
“fire” a plunger (Figure 4) at the top of the
tube, producing the sound.
In my quest to understand more about the
unit, I set out to determine the fundamental
frequency of each tube, and therefore its
musical tone. I searched the “net” and came up
with a number of sites dedicated to wind
chimes, but not much on door chimes specifically.
Although rather interesting (see sidebar), it was not critical
in the rebuild process since we wanted the same melody
as before. Nonetheless, I estimated the notes to be G, C,
D, and E (subject to verification). Some time with a small
wooden stick and a lot of banging on the bells, we
reproduced the original melody (E, C, D, G, pause, G, D,
E, C). It was now time to go through my parts bins. I found
a small eight-bit PIC (16F627A); it had two eight-bit ports,
an internal oscillator option, external interrupt pin, and
sleep function. I also found a bunch of small SSRs (
Solid-State Relays) of unknown specifications (a ham flea market
treasure). No problem!
A bit of empirical
testing (abused the
crap out of one) proved
they could handle way
more than what was
required here. I had lots
of other passive parts in
various drawers, so I
should be all set. This
should be easy!!
The PIC and SSRs
require 5V; the SSR’s FIGURE 2. Frame, circuit board, and sequencer motor.
FIGURE 1. Bottom view showing striker solenoids.
May 2017 31
FIGURE 3. Outside lighted
Determining resonant frequencies of the bells is actually not a simple matter.
Charts (and MUCH more) for wind chimes using open-ended tubes can be found at
http://leehite.org/Chimes.htm as well as many other sites.
Unfortunately, most of them cannot be applied to a bell with a closed end. A
bell with open ends produces an antinode (the position of maximum displacement
in a standing wave system) on both ends, while a tube with a plug in one end will
produce a node on the closed end. More on this can be found at www.study
Interestingly, some of this sound theory is very similar to antenna properties.
Not totally surprising, of course, since both involve waves but in a different
To post comments on this article and find any associated files and/or downloads,
go to www.nutsvolts.com/magazine/issue/2017/05.