The Metal Checker is a cool electronics device to build with an Arduino and some easy-to-obtain electronic parts. You can build the electronic circuit on an ordinary breadboard or the MakerShield. Building the Metal Checker on the MakerShield allows the device to fit nicely inside a Maker’s toolbox or workbench drawers. Also, the MakerShield is small enough to carry with you in the field for scientific metal checking activities. Figure 11-2 provides a Fritzing diagram for building the Metal Checker.
Figure 11-2. The Metal Checker Fritzing diagram
WHY USE A TRANSISTOR AND ARDUINO FOR A METAL CHECKER?
A simple Metal Checker can easily be built using an LED, a battery, and wire. So why bother using an Arduino and a transistor? Based on the metal’s electrical conductive properties, the transistor’s external base resistor will set an appropriate sensing current to turn the transistor on. The transistor provides an approximate voltage value of +5VDC to the Arduino. Upon detecting the +5VDC signal, the Arduino turns on the piezo buzzer. Therefore, the transistor acts as an electronic switch, sensitive to certain amounts of electrical current flowing through the metal. The electronic switching and sensing functions can be adjusted based on the type of metal. Also, different piezo buzzer sounds can be programmed into the Arduino to reflect various metals as well.
A simple Metal Checker cannot be modified to have such cool detecting features because of the limited parts used.
The Metal Checker uses a small transistor for metal sensing. To correctly wire it with the Arduino, Figure 11-3 shows a picture with the proper transistor pinout. Use both the Fritzing diagram and the transistor pinout to ensure correct attachment to the Arduino.
Figure 11-3. The 2N3904 NPN transistor pinout
Although the Fritzing diagram shows the breadboard and electronic components wired separately from the Arduino, the device can easily be built on a MakerShield, as shown in Figure 11-1.
TECH NOTE
Check your wiring for errors using the Fritzing diagram before applying power to the circuit.
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