Video Wireless Transmitter

To design and build a wireless transmitter that works over the FM frequency and allows the transfer of a video/audio signal over a certain distance to an FM tuner.  Click on this image to enlarge   In this fast-paced world, there is little time for inconveniences and a greater need for portability and adaptability. The idea for an Audio/Video transmitter stems from this need. There may have been times when you've wanted to hook up your VCR from one room to another television set in another room. But that would have entailed that you first unhook all kinds of wires and plugs from the primary TV set; carry the VCR to the next TV...

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Tube Li Amplifier

The unit is powered directly from the 120 volt AC line, with no power transformers. Filaments are wired in series, with the total adding up to 117 volts (35 + 35 + 35 + 12). The 35W4 forms a half-wave rectifier, which is filtered by a three-stage RC network. The B+ for the output stage plates and screens are taken from the second capacitor, and the B+ for the preamp and phase inverter from the third capacitor in the filter.  The input signal to the amplifier is applied directly to the volume control pot, from whence it passes through a variable high-pass filter (the "Treble" control). When the wiper is set to minimum, response is approximately...

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Rain Detector Using Transistor

  This rain detector will give you a heads-up the instant it starts to rain, hopefully giving you time to close windows and bring in possessions.  click on this image to enlarge The battery-powered circuit draws virtually no current when the sensor is dry and the current consumption is low when the buzzer is activated so a couple of AA cells will last a long time. Alternately, a molded power supply with a simple voltage regulator to drop the voltage to 3 volts could be used. The circuit is basically a handy flasher circuit that operates well on only 3 volts using ordinary silicon transistors. When the circuit is triggered, the...

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New Models Simulate RF Circuits

Its no news to those who simulate that the accuracy of SPICE is directly related to the accuracy of the models. What may be news is that simulation of high frequency circuits well into the gigahertz range is now possible due to the introduction of some new RF SPICE models.  click on image to enlarge To illustrate the improved simulation accuracy, the RF models were used to analyze a 500 MHz oscillator (Figure 1). The  oscillator generates a relatively high power output with a very distorted output waveform (typical at power levels over the 1- 2mW range). The simulation goals were to study the start-up characteristics, oscillating...

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Smoke Detector Circuit

The A5347CA is a low-current, CMOS circuit providing all of the required features for an ionization-type smoke detector. A networking capability allows as many as 125 units to be interconnected so that if any unit senses smoke, all units will sound an alarm. In addition, special features are incorporated to facilitate alignment and test of the finished smoke detector. This device is designed to comply with Underwriters Laboratories Specification UL217.  The internal oscillator and timing circuitry keeps standby power to a minimum by powering down the device for 1.66 seconds and sensing smoke for only 10 ms. Every 24 on/off cycles, a check...

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FINGERPRINT BASED VOTING MACHINE

The complete Voting machine consists mainly of two units - (a) Control Unit and (b) Balloting Unit with cable for connecting it with Control unit. A Balloting Unit caters upto 3 candidates. Four Balloting Units linked together catering in all to 64 candidates can be used with one control unit. The control unit is kept with the Presiding Officer and the Balloting Unit is used by the voter for polling. The Balloting Unit of EVM is a small Box-like device, on top of which each candidate and his/her election symbol is listed like a big ballot paper. Against each candidate's name, a button is provided. The voter polls his vote by pressing the button...

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Voice Switching Circuit

This circuit uses an MC2830 to form a voice activated switch ( VOX ).  click on image to enlarge A traditional VOX circuit is unable to distinguish between voice and noise in the incoming signal. In a noisy environment, the switch is often triggered by noise, or the activation sensitivity must be turned down. This circuit overcomes this weakness. The switch is activated by voice level above the noise and not activated by background noise. This is done by utilizing the differences in voice and noise waveforms. Voice waveforms generally have a wide range of variation in amplitude, whereas noise waveforms are more stable. The sensitivity...

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High 800Watts Amplifier-using MOSFET

The 800 Watt AV amplifier is based on My 1kw Amplifier and shares the same topology and basic PCB layout. The only real difference is the number of Output devices that the unit uses. The 1kw design has 20 O/P devices, while the AV amplifier has 14 O/P devices. This amplifier can be used for practically any application that requires High power, low noise, distortion and excellent sound. Examples would be Sub-woofer amp, FOH stage amplifier, One channel of a very high-powered surround sound amplifier etc. The AV amplifier has four main stages of amplification. We will begin by looking at each stage in reasonable detail. click on image to enlarge  ...

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Current Sensor

High-wattage appliances like electric irons, ovens and heaters result in unnecessary power loss if left ‘on’ for hours unnoticed. Here is a circuit that senses the flow of current through the  Appliances and gives audible beeps every fifteen minutes to remind you of power-’on’ status. click on image to enlarge  This is a non-contact version of current monitor and can sense the flow of current in high-current appliances from a distance of up to 30 cm . It uses a standard step-down transformer (0- 9V, 500mA) as the current sensor. Its secondary winding is left open, while the primary winding ends are used to detect the current. The...

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Locker Security System

The project locker security system is aimed at protecting the offering box from robbery. The project is based on micro-controller AT89C51 and some associated components. The major advantage of this security system other than the available security system is that this sounds and alarm and calls to a predefined mobile number when an attempt of robbery is detected. The mobile number can be of any persons managing the offering box and there is an option for a second mobile number to which the controller makes a second call at the time of robbery. The second mobile number can be the number of police station, so police will get notified and they can...

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Low-Cost Transistorised Inverter

This is an inexpensive fully transistorised inverter capable of driving medium loads of the order of 40 to 60 watts using battery of 12V, 15 Ah or higher capacity. Transistors T1 and T2 (BC548) form a 50Hz multivibrator. click on image to enlarge For obtaining correct frequency, the values of resistors R3 and R4 may have to be changed after testing. The complementary outputs from collectors of transistors T1 and T2 are given to PNP darlington driver stages formed by transistor pairs T3-T4 and T6-T7 (utilising transistors BD140 and 2N6107). The outputs from the drivers are fed to transistors T5 and T8 (2N3055) connected for push-pull operation. Somewhat...

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Universal IR Remote Control

Here is a circuit which can switch on and switch off any appliance with the help of a common type of infra-red remote control (transmitter).  click to enlarge This circuit senses the IR pulse and then controls the appliance accordingly. The circuit functions such that a short pulse from the remote tran- smitter switches on the triac (and the load) while a longer pulse switches off the triac as also the load. The circuit is built around hex inverter IC CD 4049. When the infra-red pulse is received by the sensor, its output (Note: Here VR1 denotes the in-circuit resistance of preset VR1.) The output of multivibrator is fed to the base of...

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