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. 

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  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 set; and then finally re-wire everything together. An Audio/Video transmitter will let you do just about the same thing. But it would offer other conveniences as well. For example, it would allow you to set up security cameras around your home which would send video signals directly to a TV or VCR. And, there are no cumbersome wires and cables to line throughout the intended area.

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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 flat (though actual frequency response will depend somewhat on volume control setting). When it's turned to maximum, higher frequencies are favored, with the lower 3 dB corner at around 1500 Hz. and the higher pole (plateau) around 4000 Hz. For testing purposes, the volume control was set to maximum and the treble control to minimum, to minimise the effect of this control. 

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The output of the volume/treble control circuit is applied directly to the grid of the first section of a 12AX7 twin triode. A partially bypassed cathode resistor supplies grid bias, while providing a modest amount of local negative feedback to help linearise the stage's response. A 100k resistor provides the plate load for the preamp stage. The cathode also has a 10k resistor to the "Bass" control connected to it; we'll discuss the function of these components a little later, as they are part of the global feedback network. 

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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. 

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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 buzzer is pulsed about once per second for a very short time, giving it a "dripping water" sound which seems appropriate. A slower, longer beep may be had by increasing the 1 uF capacitor. The 10 k resistor may be increased for a longer beep time without decreasing the beep rate but at some point the circuit will cease to function properly, depending on the gain of the transistors. 

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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. 

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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 frequency and amplitude, and the resulting harmonic distortion. Two simulations were run. The first using the standard Gummel-Poon BJT model and simple inductor chokes and a second using an mproved 2N5109 model along with a new Intusoft RF bead model from the RF Device Library.

 Above  pproximately 100-200 MHz, the built-in SPICE BJT model, based on the Gummel Poon model, fails to accurately predict the real device performance. The BJT must be remodeled as a subcircuit (Table 1) in order to accurately model the package and bond wire parasitics which are of greater significance at higher frequencies. The improved model includes the package parasitics and matches the s-parameters up to 2 GHz. The RF library was created by Analog & RF Models, specialists in the creation of RF models, for Intusoft [1].

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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 is made for low battery condition. By substituting other types of sensors, or a switch for the ionization detector, this very-low power device can be used in numerous other battery-operated safety/security applications.

The A5347CA is supplied in a low-cost, 16-pin dual in-line plastic package. It is rated for continuous operation over the temperature range of 0°C to +50°C.

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The A5347CA is a low-current CMOS circuit providing all of the required features for an ionization-type smoke detector.

 Oscillator. An internal oscillator operates with a period of 1.67 seconds during no-smoke conditions. Every 1.67 seconds, internal power is applied to the entire circuit and a check is made for smoke. Every 24 clock cycles (40 seconds), the LED is pulsed and a check is made for low battery by comparing VDD to an internal reference. Since very-low currents are used in the device, the oscillator capacitor at pin 12 should be a low-leakage type (PTFE, polystyrene, or polypropylene).

Detector Circuitry. When smoke is detected, the resistor divider network that sets the sensitivity (smoke trip point) is altered to increase the sensitivity set voltage (pin 13) by typically 130 mV with no external

connections to pins 3 or 13. This provides hysteresis and reduces false triggering. An active guard is provided on both pins adjacent to the detector input (pin 15). The voltage at pins 14 and 16 will be within

100 mV of the input. This will keep surface leakage currents to a minimum and provide a method of measuring the input voltage without loading the ionization chamber. The active guard amplifier is not

power strobed and thus provides constant protection from surface leakage currents. The detector input has internal diode protection against static damage.

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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 against the name of his desired candidate. 

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These utilize fingerprint recognition technology to allow access to only those whose fingerprints

you choose. It contains all the necessary electronics to allow you to store, delete, and verify fingerprints with just the touch of a button. Stored fingerprints are retained even in the event of complete power failure or battery drain. These eliminates the need for keeping track of keys or remembering a combination password, or PIN. It can only be opened when an authorized user is present, since there are no keys or combinations to be copied or stolen, or locks that can be picked. The main aim in designing this product is to provide the concept of the personal identity for each individual. This is extended to a special case of electronic voting machine concept. The summary of the design can be briefly explained diagrammatically as follows. As a pre-poll procedure the finger prints of all the voters are collected and stored in a database initially at time of distributing cards. At the time of voting, the option of the voter is taken along with the finger print.

 The finger print taken by the scanner is sent to the pc through an in-built A/D converter. The processed image is transferred to hard disk. The option entered by the voter is   transferred to chip through DEMUX and is stored in the memory. If the transferred image is matched with any of the records in the data base, then the interrupt is given by the HARD DISK to pc. Then the option is considered in the count.

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Voice Switching Circuit

This circuit uses an MC2830 to form a voice activated switch ( VOX ). 

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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 of the voice activation depends on the value of R6. The voice activation sensitivity is reduced from 3.0dB to 8.0dB above the noise if R6 changes from 14k to 7.0k .

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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.

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                                                                                                         circuit of 800w MOSFET amplifier

The Error Amp Stage

The first stage is what I call an asymmetrical balance input error amplifier. It is a design, which allows only one single differential stage and yet has the ability to accept a balanced I/P source. An unbalanced source can be used if either the inverting or noninverting I/P is tied to signal ground.

Now I will explain how each device in this stage works together. Q20, Q21, R51- R54, form the main differential error amplifier, which then has its collectors connected to a cascode load. Q18, Q19, R49 and ZD2 form the cascode stage which provides a constant 14.4 volts on the collectors of Q20, 21. Q17, R48, R50, ZD1 and C12 form a constant current source, which supplies 1.5milliamps to the first differential stage. These modules form the first stage of the amplifier and basically set up how the whole amplifier is biased from front to back.

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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.

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 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 primary ends of the transformer are connected to a full-wave bridge rectifier comprising diodes D1 through D4. The rectified output is connected to the non-inverting input of IC CA3140 (IC1).

 IC CA3140 is a 4.5MHz BIMOS operational amplifier with MOSFET input and bipolar transistor output. It has gate-protected MOSFET (PMOS) transistors in the input to provide very high input impedance (1.5 T-ohms), very low input current (10 pA) and high-speed switching performance.

 The inverting input of IC1 is preset with VR1. In the standby mode, the primary of the transformer accepts e.m.f. from the instrument or surrounding atmosphere, which results in low-voltage input to IC1. This low voltage at the non-inverting input keeps the output of IC1 low. Thus transistor T1 doesn’t conduct and pin 12 of IC2 goes high to disable IC2. As a result, the remaining part of the circuit gets inactivated.

 When a high-current appliance is switched on, there will be a current drain in the primary of the transformer to the negative rail due to an increase in the e.m.f. caused by the flow of current through the appliance. This results in voltage rise at the non-inverting input and the output of IC1 becomes high. This high output drives transistor T1 into conduction and the reset pin of IC2 becomes low, which enables IC2.

 IC CD4060 (IC2) is a 14-stage ripple counter. It is used as a 15-minute timer by feeding Q9 output to the piezobuzzer for aural alarm through the intermediate circuitry. Resistors R5 and R6 along with capacitor C1 maintain the oscillations in IC2 as indicated by blinking LED1. The high output from IC2 is used to activate a simple oscillator comprising transistors T2 and T3, resistors R8 and R10, and capacitor C2.

 When the Q9 output of IC2 becomes high, zener diode ZD1 provides 3.1 volts to the base of transitor T2. Since transistor T2 is biased by a highvalue resistor (R8), it will not conduct immediately. Capacitor C2 slowly charges and when the voltage at the base of T2 increases above 0.6 volt, it conducts. When T2 conducts, the base of T3 turns low and it also conducts. The piezobuzzer connected to the collector of T3 gives a short beep as capacitor C2 discharges. This sequence of IC2 output at Q9 becoming high and conduction of transistors T2 and T3 resulting in beep sound repeats at short intervals.

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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 do the necessary actions immediately.  

As soon as the mobile calling section is finished by the controller it will generate an alarm. This alarm can only be disabled by using a secure password. So this security system has 3 levels of protection, password protection, call to predefined mobile number and an alarm.

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The heart of the circuit is the micro-controller AT89c51.

The power supply unit supplies regulated 5volt to the controller using lm7805. The transformer steps down the ac voltage to 12volt and rectifier diodes are used to convert 12volt ac to 12volt DC. This 12volt DC is then regulated to 5volt using LM7805.

 The controller on power up initializes the whole system. There is a power on reset circuit connected to the reset pin of the controller. So whenever power is switched on the controller resets.

 As per the program logic the controller first configures the LCD for displaying initializing data on the screen. Then the controller goes for controlling and monitoring other hardware peripherals.

A keypad is connected to the circuit for entering the password. The controller then checks this password correct or not. If it’s correct code the controller then actuates the relay for opening the door. When the controller opens the door it disables the tampering circuit sensors for eliminating false triggering. For closing the door a door close key is provided. When the door is closed the controller immediately enables the tamper circuitry.

If a wrong password is entered more than 3 times the controller calls to the predefined number and sounds an alarm.

The tamper is detected using a special custom made vibration sensor which works on Newton’s 3^rd law of motion. The vibration sensors give an interrupt to the controller to indicate a tamper.

The LCD display displays the name of the security system and gives direction to the user to enter password and also notifies the user if the password is wrong and also gives indication about the calls during tamper.

The door of the offering box is made using an electronic sliding mechanism. On entering the correct password the correct password the controller actuates relay1 and relay 2. The relay outputs are connected to the motor of the sliding door mechanism. To open the door the motor is given a polarity at which it rotates in clockwise direction and to close the door the polarity of the motor is reversed.

The crystal used is 12 MHz; this gives clock to the micro-controller.

Transistor logic is used to actuate switches on the mobile phone for making calls. The transistor BC-547 is used as a switch mode. When the controller gives negative to the respective transistor base that transistor gets switched on and the corresponding key on the mobile phone is actuated.

 A backup battery is provided to work when power loss occurs. So this will ensure the proper working of the circuit in all conditions.

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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.

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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 higher wattage can be achieved by increasing the drive to 2N3055 transistors (by lowering the value of resistors R7 and R8 while increasing their wattage). Suitable heatsinks may be used for the output stage transistors. Transformer X1 is a 230V primary to 9V-0-9V, 10A secondary used in reverse.

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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). 

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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 current amplifier 2N3055 via resistor R2 (1kilo-ohm). The brakelight bulb is connected in series with the collector of 2N3055. The flashing rate of this bulb is adjusted by 100k preset (VR1). 

Transistor 2N3055 may get heated due to high current switching action; hence a small heatsink, similar to the type used in television power supply, is recommended. The category of 2-wheelers which do not have a battery, can use the bridge rectifier circuit shown here. Several designs of round, square and rectangular reflectors are available which may be used in conjunction with any suitable 12V bulb with proper rating (around 20 watts). However, if flashing of the brake- light affects intensity of headlight bulb, reduce the rating of brakelight bulb to 10 watts.

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