Car Battery Charger

This charger will quickly and easily charge most any lead acid battery. The charger delivers full current until the current drawn by the battery falls to 150 mA. At this time, a lower voltage is applied to finish off and keep from over charging. When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished.

Notes

1. The circuit was meant to be powered by a power supply, which is why there is no transformer, rectifier, or filter capacitors on the schematic. There is no reason why you cannot add these.

2. A heatsink will be needed for U1.

3. To use the circuit, hook it up to a power supply/plug it in. Then, connect the battery to be charged to the output terminals. All you have to do now is push S1 (the "Start" switch), and wait for the circuit to finish.

4. If you want to use the charger without having to provide an external power supply, use the following circuit.

5. The first time you use the circuit, you should check up on it every once and a while to make sure that it is working properly and the battery is not being over charged. 

from  http://www.aaroncake.net/

FM Transmitter Bug

 Application Notes:
    This small transmitter uses a Hartley type oscillator. Normally the capacitor in the tank circuit would connect at the base of the transistor, but at VHF the base emitter capacitance of the transistor acts as a short circuit, so in effect, it still is. The coil is four turns of 18swg wire wound around a quarter inch former. The aerial tap is about one and a half turns from the supply end. Audio sensitivity is very good when used with an ECM type microphone insert.

from  radio_david@yahoo.com

Simple FM Transmitter

 Description

    This FM transmitter (FM Tx) is about the simplest and most basic FM Tx it is possible to build and have a useful transmitting range. It is surprisingly powerful despite its small component count and 3V operating voltage. It will easily penetrate over three floors of an apartment building and go over 300 meters in the open air. The circuit  we use is based on a proven Australian design. It may be tuned anywhere in the FM band. Or it may be tuned outside the commercial M band for greater privacy. (Of course this means you must modify your FM radio to  be able to receive the transmission or have a broad-band FM receiver.) The output power of this FM Tx is below the legal limits of many countries (eg, USA and Australia). However, some countries may ban ALL wireless transmissions without a license. It is the responsibility of the builder to check the legal requirements for the operation of this circuit and to obey them.

    CIRCUIT DESCRIPTION:

    The circuit is basically a radio frequency (RF) oscillator that operates around 100 MHz. Audio picked up and  amplified by the electret microphone is fed into the audio amplifier stage built around the first transistor. Output from the collector is fed into the base of the second transistor where it modulates the resonant frequency of the tank circuit (the 5 turn coil and the trimcap) by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor. The tank circuit is  connected in a Colpitts oscillator circuit.

    CIRCUIT CALIBRATION:

    Place the transmitter about 10 feet from a FM radio. Set the radio to somewhere about 89 - 90 MHz. Walk back to the Fm Tx and turn it on. Spread the winding of the coil apart by approximately 1mm from each other. No coil winding  should be touching another winding. Use a small screw driver to tune the trim cap. Remove the screwdriver from the trim screw after every adjustment so the LC circuit is not affected by stray capacitance. Or use a plastic screwdriver. If you have difficulty finding the transmitting frequency then have a second person tune up and down the FM dial after every adjustment. One full turn of the trim cap will cover its full range of capacitance from 6pF to 45pF. The normal FM band tunes in over about one tenth of the full range of the tuning cap. So it is best to adjust it in steps of 5 to 10 degrees at each turn. So tuning takes a little patience but is not difficult. The reason that there must be at least 10 ft. separation between the radio and the Tx is that the Tx emits harmonics; it does not only emit on one frequency but on several different frequencies close to each other.

    NOTE:
    You may experiment with using 6V or 9V with the circuit to see how this increases the range of the transmitter. The sensitivity may be increased by lowering the 22K resistor to 10K. Try it and see.


download pdf via electronics-lab.com
from  YMYA electronics - IZHAR FAREED

Cheap Audio Booster

download pdf via electronics-lab.com
from  YMYA electronics - IZHAR FAREED

Portable Audio Amplifiers

Description
Stereo per channel
VCC=9V;RL=4?/3W
VCC=9V;RL=8?/2W

Bridge Application
VCC=9V;RL=8?/5W
VCC=9V;RL=4?/8W

Supply Voltage min = DC3v @ 500mA
Supply Voltage max = DC12v @ 500mA
Supply Voltage recommended = DC9v @500mA

DESCRIPTION
Above circuits are based on TEA2025 is a monolithic integrated audio amplifier in a 16-pin plastic dual in line package manufactured by UTC .Circuit has an Internal Thermal Protector. It is designed for portable cassette players and radios. You can also use it as your PC Audio Amplifier. A few external components required to build this circuit. Use 9v transformer to play the circuit. But not more than DC12v. Because it can damage the amplifier IC. So build n Enjoy.

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from  YMYA electronics - IZHAR FAREED

Mini-box 2W Amplifier

Designed for self-powered 8, 4 & 2 Ohm loudspeakers
Bass-boost switch

Parts:
P1 = 10K     Log.Potentiometer
R1,R2 = 33K     1/4W Resistors
R3 = 33R     1/4W Resistor
R4 = 15K     1/4W Resistor
R5,R6 = 1K     1/4W Resistors
R7 = 680R     1/4W Resistor
R8 = 120R     1/2W Resistor
R9 = 100R     1/2W Trimmer Cermet
     
C1,C2 = 10΅F     63V Electrolytic Capacitors
C3 = 100΅F     25V Electrolytic Capacitor
C4,C7 = 470΅F     25V Electrolytic Capacitors
C5 = 47pF     63V Ceramic Capacitor
C6 = 220nF     63V Polyester Capacitor
C8 = 1000΅F     25V Electrolytic Capacitor
     
D1 = 1N4148     75V 150mA Diode
     
Q1 = BC560C     45V 100mA PNP Low noise High gain Transistor
Q2 = BC337     45V 800mA NPN Transistor
Q3 = TIP31A     60V 4A    NPN Transistor
Q4 = TIP32A     60V 4A    PNP Transistor
     
SW1     SPST switch
     
SPKR     3-5 Watt Loudspeaker, 8, 4 or 2 Ohm impedance



Device purpose:

    This amplifier was designed to be self-contained in a small loudspeaker box. It can be feed by Walkman, Mini-Disc and CD players, computers and similar devices having line or headphone output. Of course, in most cases you'll have to make two boxes to obtain stereo.
    The circuit was deliberately designed using no ICs and in a rather old-fashioned manner in order to obtain good harmonic distortion behaviour and to avoid hard to find components. The amplifier(s) can be conveniently supplied by a 12V wall plug-in transformer. Closing SW1 a bass-boost is provided but, at the same time, volume control must be increased to compensate for power loss at higher frequencies.
    In use, R9 should be carefully adjusted to provide minimal audible signal cross-over distortion consistent with minimal measured quiescent current consumption; a good compromise is to set the quiescent current at about 10-15 mA.
    To measure this current, wire a DC current meter temporarily in series with the collector of Q3.

    


Technical data:

Output power: 1.5 Watt RMS @ 8 Ohm, 2.5 Watt @ 4 Ohm, 3.5 Watt @ 2 Ohm (1KHz sinewave)

Sensitivity: 100mV input for 1.5W output @ 8 Ohm

Frequency response: 30Hz to 20KHz -1dB

Total harmonic distortion @ 1KHz & 10KHz: Below 0.2% @ 8 Ohm 1W, below 0.3% @ 4 Ohm 2W, below 0.5% @ 2 Ohm 2W.

from  redcircuits.com

25W Mosfet audio amplifier

High Quality simple unit
No need for a preamplifier

  Parts:
R1,R4 = 47K    

1/4W Resistors
R2 = 4K7     1/4W Resistors
R3 = 1K5     1/4W Resistors
R5 = 390R     1/4W Resistors
R6 = 470R     1/4W Resistors
R7 = 33K     1/4W Resistors
R8 = 150K     1/4W Resistors
R9 = 15K     1/4W Resistors
R10 = 27R     1/4W Resistors
R11 = 500R    

1/2W Trimmer Cermet
R12,R13,R16 = 10R     1/4W Resistors
R14,R15 = 220R     1/4W Resistors
R17 = 8R2     2W Resistor
R18 = R22     4W Resistor (wirewound)
     
C1 = 470nF     63V Polyester Capacitor
C2 = 330pF     63V Polystyrene Capacitor
C3,C5 = 470΅F     63V Electrolytic Capacitors
C4,C6,C8,C11 = 100nF     63V Polyester Capacitors
C7 = 100΅F     25V Electrolytic Capacitor
C9 = 10pF     63V Polystyrene Capacitor
C10 = 1΅F     63V Polyester Capacitor
     
Q1-Q5 = BC560C     45V100mA Low noise High gain PNP Transistors
Q6 = BD140     80V 1.5A PNP Transistor
Q7 = BD139        80V 1.5A NPN Transistor
Q8 = IRF532     100V 12A N-Channel Hexfet Transistor
Q9 = IRF9532     100V 10A P-Channel Hexfet Transistor

 

Parts:
R1 = 3K3     1/2W Resistor
     
C1 = 10nF     1000V Polyester Capacitor
C2,C3 = 4700΅F     50V Electrolytic Capacitors
C4,C5 = 100nF     63V Polyester Capacitors
     
D1     200V 8A Diode bridge
D2     5mm. Red LED
F1,F2     3.15A Fuses with sockets
     
T1     220V Primary, 25 + 25V Secondary 120VA Mains transformer
     
PL1     Male Mains plug
     
SW1     SPST Mains switch




    Notes:

        *Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need.
        *Q6 & Q7 must have a small U-shaped heatsink.
        *Q8 & Q9 must be mounted on heatsink.
        *Adjust R11 to set quiescent current at 100mA (best measured with an Avo-meter in series with Q8 Drain) with no input signal.
        * A correct grounding is very important to eliminate hum and ground loops. Connect in the same point the ground sides of R1, R4, R9, C3 to C8. Connect C11 at output ground. Then connect separately the input and output grounds at power supply ground.

  Technical data:

    Output power: well in excess of 25Watt RMS @ 8 Ohm (1KHz sinewave)

    Sensitivity: 200mV input for 25W output

    Frequency response: 30Hz to 20KHz -1dB

    Total harmonic distortion @ 1KHz: 0.1W 0.014%  1W 0.006%  10W 0.006%  20W 0.007%  25W   0.01%
    Total harmonic distortion @10KHz: 0.1W  0.024% 1W 0.016% 10W 0.02%  20W 0.045%  25W 

 0.07%

    Unconditionally stable on capacitive loads

from redcircuits.com