Invisible Tester. Simple Design 8


IR-DIODE-TESTER-CIRCUIT-2Title of the circuit is deliberately given because it is used for testing the Photo diodes, Infrared LEDs, Photo transistors etc working in “Silent Mode”. How can we confirm an Infrared LED is working or not. It gives No visible indication. It is working and emitting Infrared rays but the IR rays are beyond our spectral response and we can’t see it. So this simple tester will help you to check whether such devices are good or bad before using in a circuit or even during trouble shooting. Not only one function the tester doing . It can test, all diodes, Capacitors, LEDs etc. Its cost is just Rs.10 but it is a worth tool.
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Laser based Alarm System. Sensor Circuit.17


It is easy to construct a Laser based Relay activator to operate Alarm systems or to switch on CCTV or Auto Camera when there is any attempt of theft. It can be used to guard, doors, entry passages etc. The circuit uses Laser beam so that the range of the circuit is more than 10 meters and there is no false triggering.

Laser diode is similar to LED and emits Monochromatic narrow laser beam that passes long distance through air. The Laser diode requires 3 volts and around 100 mA current for getting maximum range. So the current limiting resistor must be selected as per the range. A China make low cost laser torch can be used for the purpose.
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Interruption Sensor. Sensor Circuit 9



Photo interruption Module is used in the electronic circuits of automatic packing and sealing machinery using conveyor belts. The conveyor belt having equally spaced holes passes through the slit of the module.When the hole in the belt reaches the interruption module, the circuit will be activated / de activated. Here describes the working of the Photo interruption module.

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Pulsed IR Transmitter for Phototransistor. Sensor Circuits.6


Here is an Infrared transmitter circuit for emitting pulsed IR rays with a frequency of 4.5kHz for Phototransistor based receivers. The range of the IR transmission is around 1 meter. Unlike 555 IC based IR transmitters, it uses the Phase Locked Loop (PLL) IC as an oscillator. Phototransistors are more responsive to Pulsed IR rays than direct light.
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IR Beam Alarm. Sensor Circuit.2


This is a highly sensitive broken beam alarm active both day and night. It uses invisible Infrared rays to inhibit the working of alarm generator. When the IR beam breaks, by a moving person, alarm will be activated. Ideal circuit as door protector.

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Invisible Burglar Alarm. Beginners Trial 2


You can easily make this Invisible Burglar alarm using Infrared LED and a Phototransistor. When there is no obstruction in the path of IR rays, alarm will be silent. When somebody crosses the IR beam, alarm sounds. If the IR LED and Phototransistor are enclosed in black tubes and aligned perfectly, the range of the circuit is around 1 meter.
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Familiarize Electronic Components Part II – Transistors


This section describes the features of Transistors, their working and Pin identification methods.

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