The next iteration of servo/jaw sync was introduced
by “Scary” Terry Simmons (see Resources). This clever
little analog circuit used a threshold detection system to
move the jaw (Figure 4). Essentially, if the audio
input signal was louder than a set threshold, the
servo motor was driven towards the fully open
position. If the audio signal dropped below that
threshold, the servo would seek back to the jaw
closed position (see a detailed discussion of this
circuit in the September 2008 issue of Nuts &
Volts). Carefully adjusting a number of controls
on the board sometimes allowed the circuit to
perform surprisingly well, although quite a bit of
“tweaking” was often required to get optimum
results.
As the hit and miss nature of the jaw/audio
sync was a common issue, some folks even
went so far as to make a “tone track” version of
a soundtrack to obtain more control over jaw
motion from this circuit. A tone track is created
by recording a custom stereo audio track with
the spoken dialog on one side and activation
tones on the other (Figure 5).
The tone track is only sent to the Scary
Terry and its purpose is to drive the jaw. The
other track contains the actual spoken dialog
that is sent to a speaker. Though this approach has
the advantage of better jaw/audio sync, creating it is
time-consuming, and once again makes changes to
the dialog difficult as it requires a tedious
reprogramming of the tones.
Three Levels are
Better than One
Recently, a new approach dubbed the
“Jawduino” (Figure 6) has been making the rounds.
It uses an LED VU meter and an Arduino to put a
new spin on the audio/jaw sync problem (see the
September 2017 issue of SERVO Magazine for
construction details). This interesting circuit
40 September 2017
■ FIGURE 6. Jawduino featured in the September 2017 issue
of SERVO Magazine.
■ FIGURE 5. Audacity audio editor with audio track on top and
"tone" track on the bottom.
■ FIGURE 4. Original Scary Terry talking skull control
board.
■ FIGURE 7. LED VU meter and corresponding servo
position targets.
