METAL DETECTOR CIRCUIT

Metal detector is very common devices for checking the person in shopping malls, hotels, cinema halls to ensure that person is not carrying any explosive metals or illegal things like guns, bombs etc. metal detectors can be created easily and the circuit is not that complex.

Block Diagram

The LC circuit is nothing but inductor and capacitor which is connecter in parallel. The LC circuit will trigger the proximity sensor if it detects any metal near to it. Proximity sensor will give glow the led, and also make the buzz with the help of the buzzer.

Main Components in Metal Detector Circuit

LC CIRCUIT : LC Circuit is a resonating circuit which will resonate when exact same frequency material comes near. The LC circuit consist of inductor and capacitor connected in parallel , when the capacitor is fully charged the charge of the capacitor will be given to the inductor, here inductor will have improve its magnetic field. After some time the capacitor will have no charge and current from the inductor will be given to the capacitor in a reverse polarity and capacitor will get charge and now the inductor magnetic field and current will become nil. Again charged capacitor will give current to the inductor to improve its magnetic field. Note inductor is a magnetic field storage device and capacitor is electric field storage device.

PROXIMTY SENSOR : The proximity sensor can detect the objects with out any physical interference. The proximity sensor will work same as infrared sensor, proximity also release a signal, it will not give output unless and until there is no change in the reflected back signal, If there is a change in signal it will detect and give the output accordingly. There are different proximity sensors for example to detect plastic material we can use capacitive type proximity and for metals we should use inductive type.

Circuit Diagram

Circuit Working

• When the LC circuit that is L1 and C1 has got any resonating frequency from any metal which is near to it, electric field will be created which will lead to induces current in the coil and changes in the signal flow through the coil.
• Variable resistor is used to change the proximity sensor value equal to the LC circuit, it is better to check the value when there is coil not near to the metal. When the metal is detected the LC circuit will have changed signal. The changed signal is given to the proximity detector (TDA 0161), which will detect the change in the signal and react accordingly. The output of the proximity sensor will be of 1mA when there is no metal detected and it will be around 10mA when coil is near to the metal
• When the output pin is high the resistor R3 will provide positive voltage to transistor Q1. Q1 will be turned on and led will glow and buzzer will give the buzz. Resistor r2 is used to limit the current flow.

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Heat Detector Alarm using UM3561 Circuit Diagram

A very simple heat detector alarm electronic project can be designed using the UM3561 sound generator circuit and some other common electronic parts . This heat detector electronic circuit project uses a complementary pair comprising npn and pnp transistor to detect heat Collector of T1 transistor is connected to the base of the T2 transistor , while the collector of T2 transistor is connected to RL1 relay T3 and T4 transistors connected in darlington configuration are used to amplify the audio signal from the UM3561 ic.

When the temperature close to the T1 transistor is hot , the resistance to the emitter –collector goes low and it starts conducting . In same time T2 transistor conducts , because its base is connected to the collector of T1 transistor and the RL1 relay energized and switches on the siren which produce a fire engine alarm sound. This electronic circuit project must be powered from a 6 volts DC power supply , but the UM3561 IC is powered using a 3 volt zener diode , because the alarm sound require a 3 volts dc power supply. The relay used in this project must be a 6 volt / 100 ohms relay and the speaker must have a 8 ohms load and 1 watt power.

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Simple Active ir Motion Detector Circuit Diagram

To explore how different motion detectors operate.To successfully build and test an ambient-light-ignoring active IR motion detector.

Background

 There are a wide variety of motion detectors available currently. To allow a better understanding of motion detectors,the following section provides a detailed description of a few different types.

Ultrasonic Motion Detectors

Ultrasonic transducers can be used to detect motion in an area where there are not supposed to be any moving objects.This type of motion detector is most commonly used in burglar alarm systems since they are very effective in this application.

 Figure 1 shows the operation of an ultrasonic motiondetector. There are tw1o transducers: one emits an ultrasonicwave and the other picks up reflections from the differentobjects in the area. The reflected waves arrive at the receiverin constant phase if none of the objects in the area are moving.If something moves, the received signal is shifted in phase. 

A phase comparator detects the shifted phase and sends a triggering pulse to the alarm.Ultrasonic motion detectors have certain advantages and disadvantages when compared with other types of motion detectors. The main advantages is that they are very sensitive and extremely fast acting. However, the largest problem with this type of motion detector is that it sometimes responds to normal environmental vibration that can be caused by a passing car or a plane overhead. Some types of motion detectors use infrared sensors to avoid this problem, but even these detectors have some problems.

 Passive Infrared Motion DetectorIn passive infrared motion detectors, a sensorcontaining an infrared-sensitive phototransistor is placed in thearea to be protected. Circuitry within the sensor detects theinfrared radiation emitted by the intruder`s body and triggersthe alarm. 

The problem with using this type of detector is that it can be falsely triggered by warm air movement or other disturbances that can alter the infrared radiation levels in an area. In order to prevent this problem, newer systems use tw1oinfrared sensors which monitor different zones within a protected area. Logic within system triggers the alarm only when the tw1o zones are activated in sequence, as would occur if a person walked through the protected area.

Active Infrared Motion Detector

Figure 2 shows the operation of an active infrared motion detector. In the active system each sensor consists oftw1o housings. One housing contains an infrared-emitting diode and an infrared-sensitive photo transistor. The other housing contains an infrared reflector.When positioned in front of an entrance to a protected area, the tw1o housings establish an invisible beam. A person entering the area interrupts the beam causing an alarm to be triggered. An active motion detector is much more reliable than a passive one, but it requires careful alignment when it is installed. The detector can be falsely triggered if one of the housings moves slightly and causes a discontinuous beam.

Project

 For our project, we decided to construct an activeinfrared motion detector. Originally, we wanted to build both anIR and an ultrasonic detector, but we decided that an ultrasonicdetector would require too much time for a three week project.However, we also decided that just building an IR motiondetector would probably be a trivial exercise. 

So, we decided to expand on the concept by building an ambient light ignoring motion detector.This type of motion detector uses the same basic concept as the active infrared motion detector. An interruption in a 5kHz modulated pulsating beam that is transmitted by an infrared diode and received by an infrared transistor sets off the alarm. A schematic of this motion detector is given in Figure 3.

 Figure 3. Ambient-Light-Ignoring Active Motion Detector

The circuit on the left is the transmitter circuit that establishes a 5 kHz modulated infrared beam. As you can see from the schematic of the receiver circuit, a resonance-handbarrow amplifier reduces the detector`s sensitivity to stray light. C1 and L1 in IC2A`s feedback loop cause the op amp to pass only those frequencies at or near the LED`s 5 kHz modulation rate. IC2B`s output increases when the received signal is sufficient to drop the negative voltage across C2 below the reference set by R2. The output of this circuit is then attached to some load resistance, which can be an alarm or, for demonstration purposes, an LED.

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New Frost Detector Temperature Sensor Circuit

The choice has again been made for a type that we have already used in many previous Elektor circuits, the LM35CZ (-40 to 110 °C). This sensor is not expensive and generates an output voltage that is proportional to the temperature in degrees Celsius (10 mV/°C).

Sensor
An LM35 is normally powered from a single-ended power supply and 0 °C corresponds to an output voltage of 0 V. It is therefore not possible to measure negative temperatures with an LM35 in the standard application circuit. It is however possible to measure negative temperatures if its output is connected to a negative supply voltage via a resistor. There needs to be a current of 50 μA through this resistor (R2 in the schematic).

We only need to detect the freezing point with this circuit. That is why there is a comparator after the temperature sensor, which turns an LED on if the temperature has dropped below 0 °C during the course of the night. To ensure that the comparator operates properly it is necessary that the measurement value can become slightly more negative with respect to the input. To solve this problem, a diode (D1) has been connected in series with the ground connection of the LM35. The voltage drop across D1 (because of the small current through the LM35 this is only 0.47 V) acts as negative power supply. Since the non-inverting input of comparatorIC2 is connected via R3 to the anode of D1 it functions as the 0°C-reference level for the comparator.

Comparator
The comparator is a standard opamp type TLC271, which we configured for minimal current consumption by
connecting the bias-select input (pin 8) to the power supply voltage. There is no need for the detector to be fast and it will therefore work well with the opamp operating in its most economical mode.

LED D3 provides the frost indication. It is the intention that the LED stays on once the temperature in the room drops below freezing or when it has been below freezing. To realise this, an asymmetric hysteresis is created with the aid of R3, R4 and D2. The instant that the output goes high, the non-inverting input goes more positive via D2 and R4, and the output therefore stays high. The temperature would now have to increase to more than about 30° before the LED will go out by itself. In practice this probably means that it is summer and that it is not likely to freeze anyway. If need be, the hysteresis can be increased by increasing the value of R3.

Capacitor C2 is added to make sure that the LED remains off (the circuit is reset) when the power supply is connected. The non-inverting input of the opamp is briefly connected to ground and the output is therefore low. R1 and S1 are only required if the circuit needs to be reset when the battery is connected. Instead of S1 you could also use a power supply switch or even just simply disconnect the battery for a moment.

Thrifty Power supply
Since the circuit is assumed to be powered from a battery there was a conscious effort to minimise the power consumption. The current consumption of the prototype, at a power supply voltage ranging from 6 to 9 V, was less than 120 μA. When the LED is on, the current consumption rises to only 1 mA at 6V and 1.8 mA at 9V, because a low current LED is used. In our prototype we used a green, low-current LED.

If four AA penlight batteries (with a capacity of about 2 Ah) are used, then the circuit will run for about two years in standby mode. When the LED is on this is considerably shorter, of course (about two months, this is easily long enough to run through a severe winter period). A standard 9-V battery will also last a single winter, provided you frequently check whether the LED is on.

Finally, a comment about the TLC-271CP used here. The version with the C-suffix is specified for an operating range from 0 to 70 °C, but will continue to work at lower temperatures, particularly considering that the IC is not used in a linear application. If in doubt you can always try to get your hands on a version with the I-suffix (that is, TLC271IP: –40 to 125°C). But that is only necessary if you expect it to be real cold in the monitored room...

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Sensor and Detector Liquids Circuit Diagram

This is a very simple liquid detector which controls a relay, this gives you the option to be used for hundreds of applications. You can use it as a float switch to turn on the water pump alarm, rain, etc.. He uses a 4093 IC and transistor can be anyone, provided that it meets the power relay. This sensor can be used with Arduino no problem .

Sensor and Detector Liquids Circuit Diagram

 

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