Environmental Monitoring with Arduino

What Are We Measuring with This Gadget?

Now that you’ve successfully built the mobile EMI detector, we can explain what it is measuring.

Arduino’s analog input normally takes a reading of the electrical energy coming into the analog port. But because we have connected an antenna to that port, the antenna is absorbing electrical voltage from the radio signals given off by electronic equipment, and directing it into the analog port.

Arduino analog’s port can take voltage from zero to a maximum of 5 volts, and it measures this voltage in 1024 discrete slices (making each slice worth 0.0048828 volts). For example, when Arduino tells us that the reading from the analog port is, say, 250, it is telling us that the antenna wire is picking up 1.2207 volts of EMI energy (250 × 0.0048828).

The Truth Is Out There

Do a little online research into EMI detectors (sometimes called EMF detectors), and you’ll quickly discover people who claim to use electromagnetic disturbances to “detect” paranormal activity such as ghosts, poltergeists, and spirits.

Sorry to go all Scully on you, but we’ve yet to encounter compelling evidence that ghosts exist—or, if they do, that they obey the rules of electromagnetic propagation.

Anyone who wishes to use this EMI detector to go ghost hunting probably can’t be stopped. But please: don’t contact us for advice or argument, and don’t say you read it here first.

The raw number from the analog port is then sent to the speaker, where it is converted to a tone, and to the ...