AC Line Current Detector Circuit Schematic Diagram

Description

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. I tested the circuit using a 2 wire extension cord which I had separated the twin wires a small distance with an exacto knife to allow the U-bolt to encircle only one wire.

The magnetic pickup (U-bolt) produces about 4 millivolts peak for a AC line current of 250 mA, or AC load of around 30 watts. The signal from the pickup is raised about 200 times at the output of the op-amp pin 7 which is then peak detected by the capacitor and diode connected to pin 7. The second op-amp is used as a comparator which detects a voltage rise greater than the diode drop. The minimum signal needed to cause the comparator stage output to switch positive is around 800 mV peak which corresponds to about a 30 watt load on the AC line. The output 1458 op-amp will only swing within a couple volts of ground so a voltage divider (1K/470) is used to reduce the no-signal voltage to about 0.7 volts. An additional diode is added in series with the transistor base to ensure it turns off when the op-amp voltage is 2 volts. You may get a little bit of relay chatter if the AC load is close to the switching point so a larger load of 50 watts or more is recommended. The sensitivity could be increased by adding more turns to the pickup. 

Circuit Schematic Diagram

Source -  http://www.electronguide.com/circuits_pages/ACLineCurrentDetector.html

11:11 0 comments

Overheat Detector Alarm Switch Circuit Diagram

Description

At the heart of this overhead detector (fire alarm) circuit is a precision integrated temperature sensor type LM35 (IC1), which provides an accurately linear and directly proportional output in mV, over the zero to +155 degrees C temperature range. This can be used as part of fire smoke detectors but do not use it as a home fire alarm system.
The LM35 develops an output voltage of 10 mV/K change in measured temperature.
Designed to draw a minimal current of its own, the LM35 has very low self heating in still air.

 Here the output of the LM35 is applied to the non-inverting input of a comparator wired around a CA3130 opamp (IC2). A voltage divider network R3-P1 sets the threshold voltage, at the inverting input of the opamp. The threshold voltage determines the adjustable temperature trip level at which the circuit is activated.

When the measured temperature exceeds the user-defined level, the comparator pulls its output High to approx. 2.2 V causing transistor T1 to be forward biased instantly. T2 is also switched on, supplying the oscillator circuit around IC3 with sufficient voltage to start working. The 555 set up in astable mode directly drives active piezoelectric buzzer Bz1 to raise a loud alert. Components R7, R8 and C4 determine the on/off rhythm of the sounder.

Circuit Diagram

A transistor based relay driver may be driven off the emitter of T1 (TP1). Similarly, replacing the piezo sounder with a suitable relay allows switching of high-power flashers, sirens or horns working on the AC mains supply.

Source - http://electroschematics.com/699/overheat-detector-alarm-switch/

09:16 0 comments

Proximity detector circuit

NE567  tone decoder / PLL IC.

NE567 is a tone decoder IC from Philips. The IC has a built in PLL circuit with AM lock detection and an output driver circuit. The main function of NE567 is to drive a load (usually LED) when a frequency with in its detection band is available at the IC’s input. Center frequency of the input frequency band, output delay etc can be programmed using external components. The features of NE567 IC includes 0.01Hz to 500KHz frequency range, highly stable centre frequency, programmable bandwidth, high noise rejection, can sink 100mA at the output, highly immune to false triggering, externally adjustable VCO frequency etc. The common applications of NE567 are touch tone decoding, remote controls, ultrasonic controls, frequency monitoring etc.

NE567 proximity detector circuit.

 A simple proximity detector circuit using NE567 is shown here. Pin 8 is the output terminal of the internal output driver circuit inside the IC. This pin goes low when the input frequency to the IC (at pin3) is with in the detection band. Resistor R7  and capacitor C4 sets the frequency of oscillations. These oscillations are available at pin 5 and it is coupled to the terminal A of the pick up assembly using capacitor C3. Terminal B picks up the oscillations and couples it to the base of the transistor Q1 through capacitor C1. Q1 and Q2 forms a two stage collector to base biased 2 stage amplifier. R1 and R4 are the collector to base biasing resistors for Q1 and Q2. C2 couples the output of first stage to the second stage. The picked up signal is thus amplified and applied to the input pin (pin3) of the IC through capacitor C7. C6 forms the output filter capacitor and capacitor C5 determines the band width of the receiving signal. C9 is a power supply by pass capacitor. C2 and R2 provides a phase shift to the VCO signal from the IC and this phase shifted signal is detected by the IC. When some object comes near the pick up assembly, the capacitance between its terminals change. This change in capacitance changes the frequency ,IC detects this change and shows the indication.  Resistor R8 limits the output LED current.

 Notes.

• Use 9V DC for powering the circuit.
• If you are using an AC adapter, then it must be well regulated and free from noise.
• The pick up assembly can be made using two metal strips.
• POT R6 can be used for adjusting the sensitivity.

Source  - http://www.circuitstoday.com/proximity-detector-circuit

09:18 0 comments

Metal sensor detector circuit schematic with TDA2822

The metal detector circuit is shown here that the limits represent the sake of simplicity for a metal detector, but the design works remarkably well. It only uses 40,106 Hex Schmitt inverter IC, a capacitor and a search coil – and of course batteries. An advantage of IC1b Pin 4 is to be connected to a medium-wave radio antenna, or it should be wrapped around the radio. It can also be used as a hand-held metal detectors. As you can see what metal a good selection of beat-frequency operation (BFO), up to 90 mm for a bottle-top. In fact, for the ultimate in simplicity, the capacitor C1 is omitted. In this way, the author reaches is astonishing, 150mm range for the bottle top. But with the frequency then to more than 4 MHz, the instability is a major problem.

 metal detector circuit

 As shown in the circuit, oscillates at 230kHz. You can also experiment with the frequency by changing the value of C1. Faraday shield can be added to reduce ground-effect and capacitive coupling, and this is connected to 0V.
Since the inductance is resistance to rapid change in voltage, the charging of fees C1 delayed a bit like the logical level IC1a 2-pole change. This requires a rapid oscillations, which is repealed by an AM radio. Any change in the inductance in the search coil (by the presence of metal) to a change in the oscillator frequency. Although 230kHz is out of reach for the medium-wave band, an AM radio will significantly increase this frequency harmonics.

Metal detector calibration
This makes the search coil L1 is much room for error and is not far from conclusive. The author uses seventy turns 30 s.w.g. (0,315 mm) copper wire on a former 120mm diameter.
The metal detector, set up by the AM radio to pick up a whistle. Not all of these harmonic functions well, and are best suited to. The presence of metal will significantly change the sound of the whistle.

* Metal Detector FAQ *
This is not an industry or security metal detector and is not even near loma or ERIEZ metal detection system. It’s just a notebook, but not hand-metal detector.

Source  http://www.free-circuit.com

10:56 3 comments

Cell phone detector circuit diagram

This cell phone detector circuit can sense the presence of an activated mobile cell phone from a distance of one and-a-half meters.
If a RF signal is detected the circuit will inform you using a sound alarm (beep sound ) and a blinking LED .

In this type of circuit (that use high frequency 0.9-3Ghz ) you can not use an LC circuit for frequency tuning  .
The circuit uses a 0.22μF disk capacitor (C3) to according the RF circuit to ensure the capability of the circuit to capture the mobile phone signal .
This cellular phone detector can detect any activity of a mobile phone : incoming or outgoing SMS , video transmission or voice transmission .
The C3 capacitor must have leads length of 18 mm with 8 mm spacing between leads to obtain the desired frequency .  This small disk capacitor acts as a small gigahertz loop antenna to collect the RF signals  .
The CA3130 operational amplifier IC is used as a current to voltage converter .
This cellular phone detector electronic circuit diagram can be used to verify the presence of an active cellular phone in the tested area 

 

Source http://www.electroniq.net

10:48 1 comments