Although few people still own them, most heave heard of the infamous Clapper, a device that allowed for up to two other devices to be activated or deactivated via a sequence of either two or three claps. For example, two claps could turn on a lamp and three claps could activate a TV. Here’s an overview of how that process actually works and why the $20 Clapper still sells tens of thousands of units 30 years after its 1985 debut.
But how does this occur? Sound-activated products weren’t exactly new-age in the 1980’s, but the Clapper’s ability to distinguish between sounds using relatively cheap electronic components is somewhat ingenious. A Clapper’s plastic outside houses a microphone, an electronic sound filter and two electrical switches.
The microphone is mounted at the front of the device and is always powered on. Every sound that it detects is transferred to an electrical signal that is in turn sent to the electronic sound filter. The filter is set to recognize only sounds that fall within 2200 and 2800 hertz; this is the frequency range in which claps fall. When the filter registers a clap, it creates a signal that is sent to one of its two electrical switches. Each of these switches corresponds to one of the two electrical outlets on the Clapper’s exterior, where radios, TV’s, lamps, etc. are plugged in. These switches are cued to activate given a particular number of claps, and that amount of claps only. Two clap signals activate one switch, three activate the other. Deactivating a switch follows the same process.
A pretty interesting feat of engineering, but a finicky one. Claps have to be loud enough and spaced with the right timing to be read correctly by the machine, and the process of figuring out what timing worked was a notoriously frustrating one; people who clapped to quickly would often set off the two-clap switch instead of the three-clap switch, potentially turning off lights instead of a TV. The manual claims that a half-second must pass between claps to ensure that the second (of third) clap is read as a second (or third) signal.
In order to clarify this process, Clappers come with “clap detection” lights that glow whenever clap is registered. That way human clappers can know what mechanical Clappers are picking up and adjust accordingly.
Clappers also come with a dial that allows for sound sensitivity to be adjusted.
Another issue Clapper came across was that its projected clientele, which was composed of primarily elderly and disabled people, were likely to not be able to clap. They thought of a solution to this as well, recommending that such clients purchase a “cricket” or handheld metal device that makes loud clicking noises that register as claps for the sound filter.
The Clapper even has a burglar alarm setting that allows for users to set their “home” toggle to “away”, making the Clapper ultra sensitive. The idea is that a burglar making noise might activate the lights and TV, spooking him or her out of the house.