Environmental Monitoring with Arduino

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? ...