Chapter 4. Detecting Electromagnetic Interference (and making bad music)

The gadget we’re going to build next can detect electromagnetic interference (EMI), and give you a rough idea of the intensity of the EMI signal.

EMI is a form of electromagnetic radiation: a combination of electric and magnetic waves traveling outward from anywhere that an electrical power signal is changing or being turned on and off rapidly.

Sometimes, an electrical device that has the potential to give off EMI is very carefully shielded to prevent the interference from escaping; however, a great many devices that emit EMI are shielded not at all or very lightly.

Since EMI is a type of radio signal, this gadget is essentially a type of radio. We won’t be listening for any particular station or program, however. We’re listening for electromagnetic energy being emitted from various electronic devices in the local environment, and converting that into an output that our human senses can detect.

Where this gadget excels is spotting “phantom” or “vampire” energy loads. More correctly called standby power, this is the amount of electricity that constantly flows through some electronic devices, even when they’re supposedly switched off or in standby mode. Devices use standby power on features such as digital clocks, remote control reception, and thermometers. Relatively weak energy efficiency regulations in the United States result in many devices drawing far more wattage than they need in standby mode.

The result? Phantom load accounts for 10% or more of the average U.S. household’s home energy use. In 2009, that added $15.65 billion or more to the nation’s domestic electric bill (about $125 a year per household), as well as 836 million metric tons of greenhouse gas pollution to the atmosphere.

Once you’ve found the energy vampires, a brief guide from NRDC’s Smarter Living website and the “Energy Savers” booklet from the U.S. Department of Energy offer tips to cut back their energy use. But the easiest way to start curbing pollution and saving money is to pull the plug.

Detecting EMI Sources in the Environment

Moving the EMI detector around our home offices revealed a fascinating variety of unsuspected energy vampires. The Toshiba laptop computer we use for development gives off a phenomenal amount of EMI. The office television, a 1998 cathode ray tube model from Sony, gave off even more. This makes sense, because the TV is essentially built to give off EMI. (That light-saber-like hum you hear from very old televisions? EMI artifacts.)

Strangely enough, the WiFi router emitted very little EMI, at least in the range that this detector can spot.

The most surprising phantom load that we found with the EMI detector came from the office stereo system, a component bookshelf model. The 4Char lit up and the speaker squealed from several feet away.

It turns out that the stereo system uses nearly as much electricity turned off as our netbook does turned on.

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