Ideas for Areas to Explore

• Vary the coil size and windings to see how this affects the sensitivity.
• Improve the magnetometer value as it currently only makes use of the z dimension.
• Add a recent peak feature to the voltage bar graph and magnetometer circle.
• If you are using the CPB without a screen:
  • Add some audio cues as time passes when the left button is depressed to give an indication of the current menu option.
  • Conditionally disable the screen update code for a faster main loop or for better voltage stability from increased sampling. The TFT Gizmo screen is not designed to be detectable but the approach outlined in Adafruit Forums: Is it possible to detect presence of Gizmo? is likely to work.

Related Projects

• Adafruit Learn: Wireless Inductive Power Night Light
• Adafruit Learn: Cell Phone Charging Purse
• Adafruit Learn: Babel Fish - RFID language learning toy with sound.
• Adafruit Learn: Unlock Android Phone with Wearable NFC
• Adafruit Learn: Portal Apple Watch Charger
• Adafruit Blog: How to Build Your Own Metal Detector - a project on Instructables which uses a portion of a Dotstar strip to indicate finds.

Further Reading

• TDK:
  • Electronics ABC: Inductors
  • The Wonders of electromagnetism
  • Ferrite World
• UniServeScienceVIDEO: 2D Magnetic Field Demonstrations Simple Wire Coils (YouTube) - shows the magnetic field patterns around different types of coils.
• EEWeb Inductor Calculator
• Digi-Key: Protecting Inputs in Digital Electronics
• Adafruit Learn: Power Supplies - talks about how transformers work.
• Adafruit Learn: Collin's Lab: RFID (YouTube and transcript)
• Adafruit Learn: Choosing an ADC - describes internal architecture, operation and imperfections of analogue-to-digital converters.
• Analog Devices: Which ADC Architecture Is Right for Your Application?
• Adafruit: Circuit Playground: N is for Noise (YouTube)
• Andreas Spiess: How good are the ADCs inside Arduinos, ESP8266, and ESP32? And extenal ADCs (ADS1115) (YouTube) -  a look at how ADCs work.
• Adafruit SensorLab - Magnetometer Calibration
• Huygens Optics: Metal detector target discrimination explained (YouTube) - explains the double-D coil design and the discrimination by phase and has some examples of different types of magnetic material. Featured on Hackaday: Progressive or Thrash: How Metal Detectors Discriminate.
• David Hughes: On an induction-currents balance, and experimental researches made therewith (1879) - one of the earliest metal detectors.
• Duuuani, Boxall, Purvis, Madge, Banerjee: A Pulse Induction Metal Detector (2006?) - a university project constructing a metal detector.
• EEVblog #714 - Metal Detector Reverse Engineering (YouTube) - circuit analysis of an inexpensive, hand-held detector.
• Applied Science: How anti-theft tags work - magnetostriction (YouTube) - a very good demonstration of acousto-magnetic tags.
• Lecture 20: Inductance and RL Circuit | 8.02 Electricity and Magnetism, Spring 2002 (Walter Lewin) (YouTube) - a university lecture on inductance, very detailed but mostly theoretical, demonstrations at 28:56 and 49:20.
• Professor Eric Laithwaite: Magnetic River 1975 - a practical look at electromagnetism and magnetic levitation (maglev).
• Physics Girl: Why outlets spark when unplugging - EMF and Inductors (YouTube) - demonstration and explanation of arcing due to back EMF from very large inductor, plus brief reference to another video on oxygen's paramagnetism.