The application is designed to connect the simple circuits of a metal detector to an iPhone through the phone’s headphone jack. The schematics of homemade metal detectors are EXTREMELY SIMPLE and can be made by anyone, even by someone who's never held a soldering iron. Metal detectors can detect ferrous and non-ferrous metals (including gold and silver) and are able to distinguish between them (with discrimination). A positive number means it's a ferrous metal, while a negative number means non-ferrous. The numbers shown on the screen are NOT "Target ID" or VDI, like they are on brand metal detectors. The first scheme (WITHOUT CHIP) is named "Very simple" metal detector (MD1), and the second is "Sensitive" metal detector (MD2). THE "VERY SIMPLE" METAL DETECTOR IS PERHAPS THE SIMPLEST SCHEME OF AN ACTUAL, WORKING METAL DETECTOR, FOR IT ONLY CONSISTS OF AN LC CIRCUIT AND TWO RESISTORS IF YOU DON'T COUNT IN THE IPHONE :). The main part of the device is the LC circuit. The stability of its parameters is very important. They constantly fluctuate with the slightest changes in temperature. Moreover, the inductance changes with the slightest changes in the geometry of the inductance coil. These changes are constantly being adjusted by the application. The parameters of the internal iPhone circuits and the headphone jack adapter can also fluctuate, but they stabilize after approximately 2-3 minutes after turning on the signal (therefore, the metal detector must work continuously during the search). Frequency range is 3-14 kHz. It is possible to choose the frequency by choosing the capacity of the condenser in the LC circuit. After a change in capacity or inductance, on the first start, or when a change in air temperature occurs (for example, when you went outside), you need to enable the search for the resonance frequency. Searching using a metal detector isn't as easy as it might seem and might sometimes be deadly. Therefore, it is necessary to study this subject on specialized sites. Be sure to do some experiments with a coin placed on the ground. FREE VERSIONS OF METAL DETECTORS ARE LIMITED BY THRESHOLD OF THE SOUND SIGNAL AND THE INDICATOR LIGHT. WHICH MEANS THAT IT'S POSSIBLE TO DETECT THE METAL BY THE NUMBERS (THE FONT SIZE OF WHICH IS REDUCED) ON THE IPHONE'S SCREEN, BUT IT CANNOT BE HEARD OR SEEN IN PERIPHERAL VISION IF NOT LOOKING DIRECTLY AT THE SCREEN. "Very simple" metal detector (WITHOUT CHIP): • Coin: 4 inches (10 cm) • Small shovel: 6 1/2 inches (16 cm) • Discriminate between metals "Sensitive" metal detector: • Coin: 6 1/2 inches (16 cm) • Small shovel: 9 inches (23 cm) • Discriminate between metals