Voltage

Static charge-electricity detector

The detector will sense static charges and free ions in the air. It can be used to indicate the presence of ion emission, high voltage, static electricity, and electrostatic fields. The ground can be an earth ground or a touching metal by your hand. the meter is 100uA range. and R3 potentiometer is by controlling the sensitivity of the detector...

AC current Detector schematic

This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 800 turns of #30 - #35 magnet wire. The pickup could be made from other iron type rings or transformer cores that allows enough space to pass one of the AC lines through the center. Only one of the current carrying lines, either the line or the neutral should be put through the center of the pickup to avoid the fields cancelling. ..

Load detector Mains Switch

This circuit will automatically switch on several mains-powered "slave" loads when a "master" load is turned on. For example, it will switch on the amplifier and CD player in a stereo system when the receiver is turned on. It works by sensing the current draw of the "master" device through a low value high wattage resistor using a comparator. The output of that comparator then switches on the "slave" relay. The circuit can be built into a power bar, extension cord or power center to provide a convenient set of "smart" outlets that switch on when the master appliance is powered (turn on the computer monitor and the computer, printer and other peripherals come on as well)...

Current sensing relay

The current to be sensed should flow from A to B. It flows either through R1 or (if big enough) through D1. There is an anti-parallel diode also present so the circuit can be used equally well for d.c. or a.c. sensing. With the relay off, Tr1 is not conducting so Tr2 must be. Therefore Tr1 must be off. This occurs (surprise!) at zero current. The 12v supply line will cause current to flow through R3 and R2 so a voltage {12x(R2+R1)/(R1+R2+R3)} will be developed on the base of Tr1. This voltage is 390 millivolts - enough to bring Tr1 near to turn on. Any voltage developed across R1 will add to this 390mV...

Simple Electric Field Detector

The circuit will come handy when you have to follow the mains wires buried in the wall or even water pipes provided they are not too far away (2-4cm max). It will also detect a conversation on a telephone cable without actually touching it (for testing purposes only) and it works as a microphone if you keep a plastic kitchen foil between the probe tip and your mouth. The probe is just the 12mm long gate lead of the transistor. The 33M resistor should be cut short and soldered where the lead enters the transistor case. Connection to the other part of the circuit is via a standard coaxial cable of any length...

Signal and Tone Activated Relay Switch

In the Fig.1, exist a circuit, which is a sensitive switch that corresponds in AC signals of input, for signals above 5mV. Corresponds in all the signals from 50 HZ until 3KHZ, region in which found the human voice. The RV1 is regulated so much what RL1 it?s in situation OFF, when the input is it has null signal. In the Fig.2, exist a band - pass filter, coordinated in the 1KHZ, which can be placed in line in the bronchus of negative feedback, in points A, B, C, making sensitive the circuit only in this frequency. ..

under?-over voltage detector

In Fig.1 A precision DC under?voltage relay switch. The opamp is wind as a voltage comparator, with a reference voltage applied to pin 2 and the test voltage applied to pin 3: the relay turns on when the pin 3 voltage exceeds that of pin 2. The circuit can be made to trip at any voltage in excess of 5 volts by suitable choice of R1 value. In Fig. 2 An over-voltage switch that can be used to trip at any pre-set voltage in excess of about 10 mV. The input voltage can be connected directly to pin 2 if trip values in the range 10mV to 3Volts are required. For voltages in excess of 3 Volts, a suitable range resistor must be connected in the position shown, to keep the pin 2 Voltage drive to suitable level. The circuit can be converted to an under?voltage switch by transposing the pin 2 and pin 3 connections of the op-amp. ..

Mains Voltage Checker

This is a CMOS IC (CD4033) based circuit which can be used to detect presence of mains AC voltage without any electrical contact with the conductor carrying AC current/voltage. Thus it can be used to detect mains AC voltage without removing the insulation from the conductor. Just take it in the vicinity of the conductor and it would detect presence of AC voltage. If AC voltage is not present, the display would randomly show any digit (0 through 9) permanently...

Sensitive Electrostatic detector

This simple circuit can detect the invisible fields of voltage which surround all electrified objects. It acts as an electronic "electroscope." Regular foil-leaf electroscopes deal with electrostatic potentials in the range of many hundreds or thousands of volts. The above device can detect one volt. Its sensitivity is ridiculously high. Since "static electricity" in our environment is actually a matter of high voltage, this device can sense those high-voltage electrically charged objects at a great distance. On a low-humidity day and with a 1/2 meter antenna wire, its little LED-light will respond strongly when someone combs their hair at a distance of five meters or more...

LED Power Failure Light

The power failure light that I eventually designed and built is housed in the plastic case from a wall-mounted power transformer. I had accidentally destroyed the transformer by shorting its output, and had kept the plastic case for years, just waiting for a project like this one. Since its mounted in a hand-sized enclosure, when the power fails, it is a simple matter to walk over to the light, unplug it from the wall, and use it like a flashlight to walk into other rooms to retrieve a flashlight. This particular lamp dims after a few minutes, and is down to a dull glow after about 15 minutes. The glow can last for hours after that. I suspect that this is at least partly the result of using rechargeable batteries from a surplus store...

Voltage Sensitive Probe

This circuit is so sensitive it will detect "mains hum." Simply move it across any wall and it will detect where the mains cable is located. It has a gain of about 200 x 200 x 200 = 6,000,000 and will also detect static electricity and the presence of your hand without any direct contact. You will be amazed what it detects! There is static electricity EVERYWHERE! The input of this circuit is classified as very high impedance...

Reverse engineered schematic diagram of a mass produced lightning detector. The RF signal from lightning is quite strong and broad in spectrum so a tuned circuit is not required at the antenna input stage. Too much sensitivity will cause false alarms in a simple receiver such as this one. The circuit uses clever pulse timing and intergration techniques to discriminate between real lightning and other RF interference. The short antenna provides bandwidth limitation towards the low end of the spectrum, while the metal gate CMOS logic running on a mere 6 volts caps the high frequency response...

This circuit relies upon the extra high input impedance of a FET, and also demonstrates the gate terminals sensitivity to changes in voltage. The gate terminal here is left open circuit, connected only to the "probe" this being just a few inches of bare copper wire. With no fixed DC biasing, the gate terminal will respond to micro changes in voltage or "field strength". It is important not to make this circuit on veroboard or PCB material as this will reduce the effective gate impedance...

This is a CMOS IC (CD4033) based circuit which can be used to detect presence of mains AC voltage without any electrical contact with the conductor carrying AC current/voltage. Thus it can be used to detect mains AC voltage without removing the insulation from the conductor. Just take it in the vicinity of the conductor and it would detect presence of AC voltage...

This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts. It uses a LTC1440 comparator, which also contains a 1.18v reference diode. In standby mode, the circuit draws only 4uA...