Belgian Earth Fault Detector

Having been affected by earth fault accidents,  the author put together this little circuit. It  consist of just three elements: the neon with its  original resistor for example, salvaged from  the switch on an AC power bar and a small  capacitor (class Y) salvaged from the electronics of a low-consumption lamp.

A larger capacitance makes the neon glow brighter. All this  for no money at all. The neon lights only when there is an efficient Earth present. This works  well at the author’s home, with Live or Neutral either way round. In the Elektor laboratory based in The Netherlands, some concerns  were expressed as described in the June 2011  issue [1], as the circuit was sensitive to the relative positions of the Live and Neutral. So the  Earth fault detector can also be used as a Phase  detector, but probably in Belgium only.

The whole thing can easily be incorporated into a power socket; the author used a small transparent cover to protect the neon.

Note. As opposed to the UK and the US, some AC  power outlets in Belgium  and all in The  Netherlands are not polarized, i.e. AC power plugs (both earthed  and non-earthed) can be inserted either way around.

Source : http://www.ecircuitslab.com/2012/05/belgian-earth-fault-detector.html

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Home Made Metal Detector

This homemade metal detector circuit will help you find objects composed of materials with relatively high magnetic permeability. It is not suitable for buried coins discovery that is not sensitive enough but you can detect pirates treasures! The metal detector is powered by 2 x 9V batteries, each of it charges with 15mA. L1 detector coil is part of the sinusoidal oscillator built around transistor T1.

Normally, the center frequency of the voltage controlled oscillator (VCO) from the PLL loop that is contained in IC1 is equal to the oscillation frequency of T1. This changes when entering a metallic object (ferrous or nonferrous) in the field induced by L1. S1 is a miniature 2-pole switch. Meter needle deviation is a measure of frequency change, since the direction of deviation depends on the type of material detected by the coil. The meter tool used for this homemade metal detector is zero as central, +-50µA.

Metal detector circuit schematic

Coil L1 consists of 40 turns of enamelled copper wire, wound on a plastic template with a diameter of about 10 cm. Inductance thus obtained ensure the functioning of the oscillator at a frequency approximately equal to the VCO included in the PLL loop. Use an oscilloscope to check that pin 2 of IC1 delivers sinusoidal signal with frequency about 75 kHz.

Adjust P1 so that fronts rectangular signal from pin 4 to coincide with the peaks of the sinusoidal signal from pin 2. Then, adjust P2 in order to obtain 0 on the meter. Since the neutral zero setting “runs” with the battery’s decreasing voltage it will be necessary to restore it (zero balancing) from time to time during use of the metal detector.

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Motor Turn Stall Detector

In single segment AC induction motors, incessantly used in fridges and washers, a begin winding is used throughout the starting section. When the motor has reached a undeniable pace, this winding is fliped off once more. The begin winding is moderately out of segment to the run winding. The motor will best start turning when the present via this winding is out of section to that of the run winding. The phase distinction is in most cases provided with the aid of putting a capacitor of a couple of µF in series with the beginning winding. When the motor reaches a minimal pace, a centrifugal swap turns off the beginning winding. 

The circuit diagram doesn’t show a centrifugal switch; as an alternative it has a triac that's fliped on throughout the staring segment. For clarity, the sequence capacitor isn’t shown within the diagram. Once the motor flips it's going to proceed to do so so lengthy as it isn’t loaded an extreme amount of. When it has to force too heavy a load it'll virtually indisputably stall. A large current starts to waft (as the motor not generates a again EMF), which is restricted only by the resistance of the winding. This lead tos the motor to overheat after a undeniable time and result ins permanent damage. It is due to this reality essential to give you the option to observe when the motor turns, which happens to be extraordinarily easy. When the motor is popping and the start winding will no lengthyer be used, the rotation set offs a voltage on this winding.

Circuit diagram:

Motor Turn Stall Detector Circuit Diagram

This voltage will likely be out of phase since the winding is in a unique position to the run winding. When the motor ceases fliping this voltage is no longer affected and shall be in phase with the principles voltage. The graph presentations one of the relevant waveforms. More data may additionally be discovered within the utility no lengthyere for the AN2149 made through Motorola, which can additionally be downloaded from their site at www.motorola.com. We assume this accommodates some useful ideas, however keep in mind that the circuit exhibitn is only partially completed. As it stands, it for sure can’t be put straight to use. We should also draw your attention to the truth that primarys voltages can be lethal, so take great care when the primarys is connected!

Author: Karel Walraven - Copyright: Elektor July-August 2004

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