More recently, a number of reviewers have complained
about the usability of clapping switches on Amazon.
The Sonic Sensor deals with the reliability issue nicely,
and pairing the device with a microcontroller opens up
the possibility of even more exotic options.
Theoretically, detecting handclaps should be easy. The
amplitude envelope of a microphone is preamplified,
rectified, and filtered, and then a comparator trips
whenever a certain threshold is reached. Unfortunately,
various practicalities make this undertaking surprisingly
difficult, and the tradeoffs must be carefully balanced to
arrive at a truly useful gizmo. In fact, I went through three
distinct revisions and topologies before arriving at a
trustworthy circuit! As a first step, let’s see what the
design goals are.
The Sonic Sensor should:
• Have adjustable sensitivity.
• Be fast but not prone to ripple in the filtered
• Provide a gate output when sound is detected.
• Operate on +5V for easy interfacing with
• Be small enough to build as a plug-in unit for use
with breadboards, yet be as simple and inexpensive as
It took some doing, but these goals were nicely met.
Shall we see how it works?
September 2013 35
■ FIGURE 1.