Build Your Own Electromagnetic Interference (EMI) Detector

Build Your Own Electromagnetic Interference (EMI) Detector

When I started learning DIY electronics, using Arduino was the obvious choice. This palm-size, single-board microcontroller, which can be easily swapped between projects, is designed for programming novices. Yet it has more on-board processing power than the navigation computers used by Apollo astronautsâ€"and at only about $ 30 a pop.

These qualities make Arduino the go-to component for building DIY environmental-monitoring devices, such as the electromagnetic interference (EMI) detector shown here. Because it converts invisible electric vibrations into audible sound, it's handy for identifying sources of standby power: the energy that flows constantly through electronics, even when they're supposedly off. Cut the power to those electronics between uses and you'll reduce your electric bill and your carbon footprint.

When you're ready to build something new, take this gadget apart and reuse the Arduino in your next project. Try that with a watt meter from the hardware store.

Project: Electromagnetic Interference Detector
Rough Cost: $ 42
Time Commitment: About 1 hour
Skill Level: Easy
Why Make It: This is a DIY electronics skill-builder with a practical applicationâ€"reducing standby power, which adds as much as 10 percent to U.S. residential electric bills.

Parts List:

Online stores, including Maker Shed, Adafruit Industries, SparkFun, Emartee, and Electronic Goldmine, sell the parts you'll need to build this gadget. They may also be available at your local RadioShack.

• Arduino Uno microcontroller
• Standard USB A/B cable, 3 ft. or longer
• 8-ohm speaker
• 1-megaohm resistor
• Breadboard
• 3â€"5 feet of insulated solid core wire
• 9-volt battery pack
• Fresh 9-volt battery
• Small-gauge wire stripper

Part I: Download and install the Arduino software

To use Arduino, first install the free, open-source software that will let you install programs (called "sketches" in Arduino-speak) onto Arduino. This is easy to do: Find the software (available for Mac OS X, Windows, and Linux), along with instructions for installing and using it, at: arduino.cc/en/main/software

Part II: Test the 8-ohm speaker

Before we begin to build the EMI detector, be sure the 8-ohm speaker works:
• Step 1: Plug your 8-ohm speaker into Arduino as follows: the red lead into digital pin 8 and the black lead into the digital GND pin, along on the same line of pins on Arduino.
• Step 2: Connect Arduino to your computer using the USB cable. (This cable powers Arduino and lets you upload sketches fr om the Arduino software.)
• Step 3: Open the Arduino software. Find the sketch "toneMelody" at File | Examples | Digital | toneMelody. Load it onto Arduino, and run it.
Did you hear a pleasing little melody come from the 8-ohm speaker when you ran the sketch? Then it worked. If not, check all your connections and try again.

Part III: Construct the EMI detector

• Step 1: Cut a 3-foot-long piece of solid-core wire.
• Step 2: Strip about 1.5 inches of insulation from one end of the core wire.
• Step 3: Twist together one end of the 1-megaohm resistor with the stripped end of the core wire.
• Step 4: Insert the twisted-together core wire/resistor into analog pin A5 on Arduino, and insert the free end of the resistor into one of the analog GND pins on Arduino, which can be found along the same line of pins.
• Step 5: Insert one end of a jumper wire into digital port -9 on Arduino and the other to a pin on the breadboard.
• Step 6: Insert one end of another jumper wire into Ardunio's digital GND pin and the other into a pin on a different row on the breadboard.
• Step 7: Connect the red lead of the 8-ohm speaker to a pin along the same row that's wired to digital port -9 on Arduino, and connect the speaker's black lead to a pin on the row wired to the digital GND port. (Note: You could also connect the speaker directly to Arduino but using the breadboard reduces the wear and tear on Arduino and better supports the speaker when you use the detector in mobile mode.)
• Step 8: Connect Arduino to your computer with the USB cable
• Step 9: Open the Arduino software, and load the Arduino Electromagnetic Interference Detector sketch into it; you can find the sketch at < a href="https://github.com/ejgertz/EMWA/tree/master/chapter-4" target="_blank">github.com/ejgertz/emwa | chapter-4 |
• Step 10: Load this sketch onto Arduino.
• Step 11: Once you have uploaded the sketch to Arduino and Arduino restarts, you'll probably hear a cacophony of sound from the speaker. That's normal: Because Arduino is connected to your computer, it's receiving a flood of electromagnetic interference from the computer via the USB cable.
To make this detector really useful, we need to take it mobile.

Part IV: Powering the EMI Detector in Mobile Mode

• Step 1: Carefully unplug Arduino from the USB cable.
• Step 2: Snap the 9-volt battery into the battery pack, and then plug the battery pack into Arduino's power port. The Arduino should start up immediately: The LEDs mounted onto the board should flash, and within a f ew seconds the EMI code should be up and running.
• Step 3: Now take your detector for a walk around the room. While you'll hear a steady stream of white noise from the speaker, it should change in tone or squeal when the wire encounters EMI­â€"the louder or faster the noise, the more electromagnetic interference the gadget has detected.

Excerpted and adapted from Environmental Monitoring With Arduino by Emily Gertz and Patrick Di Justo, published by O'Reilly Media Inc. Copyright 2012 Emily Gertz and Patrick Di Justo. All rights reserved.

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