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Wednesday, August 6, 2008

LA4440 - 6W 2-Channel, Bridge 19W

LA4440 - 6W 2-Channel, Bridge 19W typ Audio Power Amplifier

Manufacturer: SANYO


  • Built-in 2 channels (dual) enabling use in stereo and bridge amplifier applications.
  • Dual : 6W´2 (typ.)Bridge : 19W (typ.)
  • Minimun number of external parts required.
  • Small pop noise at the time of power supply ON/OFF and good starting balance.
  • Good ripple rejection : 46dB (typ.)
  • Good channel separation.
  • Small residual noise (Rg=0).
  • Low distortion over a wide range from low frequencies to high frequencies.
  • Easy to design radiator fin.
  • Built-in audio muting function.
  • Built-in protectors.

  • a. Thermal protector
    b. Overvoltage, surge voltage protector
    c. Pin-to-pin short protector

    Pin No. Pin Name
    1 NF1
    2 IN 1
    3 Preamp. GND
    4 Audio Muting
    5 DC
    6 IN2
    7 NF2
    8 Power AMP GND2
    9 B.S2
    10 OUT2
    11 Vcc
    12 OUT1
    13 B.S1
    14 Power AMP GND1

Tuesday, August 5, 2008

FM Wireless Mike

FM Wireless Mike can transmit voice signals to any FM Radio receiver 100 meters away. The circuit is basically a frequency modulated transmitter working at 100 MHz. The frequency of the transmitter can be varied slightly by changing the trimmer C5. You can use ordinary condenser mike in this circuit. The transistors can be replaced by any low power transistors like BC148 or BF494.

The coil L1 is air core 6 turn 24 SWG. Third turn is tapped and connected to telescopic antenna. You can replace telescopic antenna with a small piece of wire.

Miniature MW Transmitter

Here is a very simple, inexpensive and interesting project which provides lot of fun to a home experimenter or hobbyist. This simple transmitter can transmit speeches or songs within a short range.

The circuit uses only one transistor. The entire circuit can be easily assembled on a prototyping printed circuit board. After assembling all the components properly put the whole assembly in a plastic enclosure provided with a telescopic antenna. Now keep your MW radio and the transmitter on a table about one meter away from each other. Switch on the radio receiver and turn to a clear spot where no broadcasting station is present. Now switch on the transmitter and turn the gang condenser. At some position loud hissing sound will be heard from your receiver. Stop the gang condenser at this position. Speak some thing to the speaker which serves as the microphone. Now turn the radio receiver to get clear and loud sound.

The transmitter have a range of 200 meters. You can increase the range by using an external antenna and sensitive receiver at receiving end.

600 Volt Power Supply For QRO

Amateur Radio Transmitters using valves such as 807 or1625 works well with a plate voltage between 600V to 700 Volts.The circuit described here is a full wave voltage doubler. The output voltage is twice the input voltage. For 230V AC input the output will be nearly 600 Volts.

Resister R1 is used to limit the initial high voltage and high currents. Capacitor C1, C2, C3 together with coils L1 and L2 form input line filter. The capacitors C4 and C5 protects diodes from high voltage transients on the AC line as well as reduces inter carrier hum modulation of the R.F picked up by the mains. Capacitors C6 and C7 provides enough filtering for the output DC Voltage.

C1, C2, C3 - 0.1 mf 630V
C4, C5 - 0.01 mf 630V
C6, C7 - 100 mf 450V
R1 - 10E 5W Wire Wound
R2, R3 - 220KE 2Watts
D1, D2 - BY127
D3, D4 - BY127
L1, L2 - 12 Turns 18 SWG
Wound over 4 Cm
long Ferrite Rode.

Ceramic Filter Beat Frequency Oscillator

BFO is a simple device which helps us to listen SSB and CW transmissions. Reception of SSB and CW signals requires a product detector or BFO (Beat Frequency Oscillator) to reinsert the missing carrier. This circuit is very simple since it requires no turned circuit and hence no adjustment in the BFO circuit. The number of components required is also very limited. To produce 455 Khz carrier a ceramic filter is used. It cost me Rs: 6/- only. The RF choke (RFC) is made by winding 150 turns of enamelled wire on half watt 150 K carbon resistor.

When receiving Single Side Band (SSB) signals the locally generated carrier beats with the SSB signal to produce the complete audio signal. Because the ceramic filter operates at fixed frequency, no turning is required to demodulate the single side band (SSB) signals and no regulated power supply is necessary. First tune your AM radio to some SSB signal and switch on the BFO and slightly adjust receiver turning for good resolved audio quality. To resolve stronger stations connect a wire not bigger than 10 cm to the out put of the beat frequency oscillator.

Most of the BC receivers use 455 KHz as IF amplifier frequency. Some receivers have an IF Frequency which lies between 450 and 460 KHz. For best result the receiver IF amplifier frequency and the beat frequency oscillator frequency should be the same.


They will be swarming once again, the unwanted, winged torturers, looking for the victims and leaving behind swelling and itch!

The mosquito problem is a part of everyday life, espacially during the summer.

Since the immemorial, inventive people have struggled hard to find effective means of protection against these insects. Even though it is a fact that only the females are dangerous, the males can also create situations of panic by their humming. Scientists say that these and many other insects find some particular frequencies of sound very unpleasent abd run away from these frequencies.

It seems quite obvious then, that by creating these insects frequencies electronically, we should be able to repel these insects! The most important point to remember here is that, unfortunately, this method has so far not been completely sucessfull. Whereas one group of insects can be made to run away at frequencies around 5 KHz, other types may desert only at higher frequencies, about 10 to 20 KHz. For some types, all the frequencies may fall on deaf ears! Yet other theories propose that in fact some frequencies may even attract them instead of repelling.

Whatever may be the truth, trial is superior to just theorising. Even though the cost of our circuit may prove to be a wrong investment, as the population of mosquitoes and insects who are immune to our insects/mosquito repellant is likely to be predominant ! The loss is very high - four resistors, two capacitors, two transistors and a buzzer.


The Astable Multivibrator, which is generally used as a signal generator, is once again used here to generate the desired frequencies. It is an excellent example of the fact, how versatile simple basic electronic circuit can be.

Let us quicklt see the operation of the astable multivibrator circuit. When T1 is conducting T2 is off and when T2 is conducting, T1 is off. The capacitors C1 and C2 contributes decisively to this ON/OFF cycles for the transistors T1 and T2. The time taken by C1 and C2 to charge and discharge decides the shape of the output waveform. Another important factor in the operation of the circuit is the fact that the transistor goes into conduction only when the base-emitter voltage exceeds 0.7 volts (for silicon transistors). From this basic knowledge we can visualise how the transistors exchange their roles and how the voltage on the collector of each transistor jumbs between the lower and upper level, producing a rectangular waveform. If you take a close look at circuit, you will notice that C1 and C2 are not equal. They differ in their values by afactor of four.

The output signal will thus be a non symmetrical waveform. Such a non symmetrical signal contains more high frequency harminics compered to the normal square wave signal. The output of our circuit will have the basic frequency of 5 KHz along with harminics of 10, 15 and 20 KHz. If some insects are deaf to frequencies upto 5 KHz, they may react to 10 KHz or 15 KHz or even 20 KHz, one never knows ...

The piezo buzzer used should not have an internal oscillator built into it. The circuit consumes 0.3 ma current, and can give about 1500 hours of nonstop operation.

R1,R4 - 10 K Ohm
R2,R3 - 560 K Ohm
C1 - 82 PF
C2 - 330 PF
T1,T2 - BC547
Piezo Buzzer (Without internal oscillator)