■ FIGURE 14. Lid test-fit back
on the jar.
■ FIGURE 15. Test-fit for clearance from
the servo horn to the bottom of the
■ FIGURE 16. Add a trigger wire to resistor
pad R3 (circled in red).
leads down through the PCB to the
center power bus. I ran the speaker
leads to a two-pin header that would
lead up to the speaker in the jar lid. I
threaded the “trigger” wire from the
R3 pad down through the PCB and
across to the P3 pad for the BASIC
Stamp 1 (Figure 17). I hot-melt glued
the record pushbutton to the back of
the servo motor (Figure 18). As a
quick test, I recorded a “hello world”
message and then wrote a small
program for the BS1 to toggle the
pin. I found a dwell of about 500 ms
was perfect to get reliable triggering
of the sound sample. So far, so good!
JUNK BOX SCAN HEAD
So now that I had sound, I started
to think about the scan head that the
servo motor would be rotating. I dug
around in the junk box and came up
with an old prescription pill bottle
with a child proof cap. I cut around
the bottle about 1/2” from the top
with a Dremel tool and then drilled
holes at four cardinal points to hold the
LEDs (Figure 19). I used two small
screws to secure the pill bottle to the
■ FIGURE 17. Trigger wire from pad R3
through the PCB to BS1 pin P3.
the servo horn (Figure 20), hot-melt
glued a small tire hub from a discarded
toy to the top (Figure 21), and voíla!
I had my high-tech scanner head.
MIXING IT UP
When I was sketching up the
original plans for this device, I had
intended to have both the audio playback from the sound recorder and
the BS1 beepy sound effects both
coming from a single speaker. I figured
I could just force feed the sound
from the BS1 to the sound board’s
speaker by loosely coupling the output pin from the BS1 to one of the
speaker leads using a small capacitor.
When I tried this, the volume from
the sound module dropped drastically
and became very distorted. I tried a
few other methods to mix the signal
from the sound playback board and
the output from the BS1 including a
small transformer and even a couple
op-amps to make a small mixer. The
circuit was getting more complicated
and the results were still pretty dismal.
I decided to take a simpler approach
and create a mechanical mixer.
■ FIGURE 18. The record button
hot-glued to side of servo.
Instead of trying to mix two signals
into one speaker, I placed a second
speaker coaxially mounted on top of
the first speaker! I did this by cutting
a ring from the remains of the pill bottle
I had used earlier for the scan head, and
then hot-melt gluing it to the existing
speaker. I then glued a small surplus
speaker I found in my junk box to that
ring (Figure 22). This method worked
very well and made the BS1 sound
effects audible right along with the
spoken dialog from the sound module.
This also meant that it would be
possible to build this device with a
second speaker grill, maybe even
facing in a different direction. This
way, the beeping effects could
appear to come from the scan head
while the dialog from the sound
module could come from near the
main LED light source. You could
even consider mounting the second
speaker on the scan head itself so the
sounds would move around as the
direction of the scan head changed.
Of course, the path I took isn’t a
requirement; you can construct your
monster detector in any container
and with any method you like. Make
■ FIGURE 19. Scan head with LEDs
mounted and servo horn attached.