Most metal detectors work on the fact that metals in a magnetic field change the behaviour of the field. There are two general approaches to detect these changes. In one approach, an alternating current is provided to a transmit coil. A receive coil is used to pick up the magnetic field generated by the transmitter. If a piece of metal comes inside the range of the
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magnetic field lines, the receive coil can detect a change in both amplitude and phase of the received signal. The amount of amplitude change and phase change is an indication for the size and distance of the metal, and can also be used to discriminate between ferrous and non-ferrous metals. In the other approach, current pulses are sent to the transmit coil. The magnetic field caused by these pulses start eddy currents in metals close to the coil. If the magnetic field is switched of fast enough, the eddy currents can be detected with the transmit coil, which then acts as a receiver. Pulse induction can often reach deeper targets than frequency based detectors, but discrimination between different types of metals is more difficult. Because of the specific needs when I started this project, this page describes a pulse induction metal detector with as much as possible discrimination between different metals. To achieve this, the processing of the signals is done entirely digitally with a digital signal processor, DSP. There are many projects floating around on the internet regarding pulse induction metal detectors. Although they differ in the way the signals are processed, the electronics which generate the magnetic field pulses is almost always identical. The main part to generate magnetic pulses is the coil. The size of the coil is mainly dependent on the required detection depth and the minimum size of objects that still...
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The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
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In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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