Wiring And Schematic

This is an old amplifier, LM383 is discontinued, so this LM383 ability be difficult to find. You can use ECG1232, TDA2002 or TDA2003 as the alter for LM383. Take a agenda that a heatsink bowl is appropriate to abstain overheating on the ICs.

A very simple electronic key code lock circuit that require few external components can be constructed using this schematic diagram . This electronic key code lock circuit is based on a common 555 timer circuit and some other common components .

This low cost key code circuit use six switches that needs to be pressed to open the lock, but only two switches at a time. In many other , more expensive electronic circuits the key code is formed by pressing some switches one by one , not like in this case two switches . If you don’t like to press two switches in the same time you can eliminate one switch , but in that case the code can be more easy to guess by someone ells .
Thus a total of three sets of switches have to be pressed in a particular sequence. (Of these three sets, one set is repeated.)

An essential property of this electronic code lock is that it works in monostable mode, i.e. once triggered, the output becomes high and remains so for a period of time, governed by the
timing components, before returning to the quiescent low state.

Pin 2 of 555 timer is the triggering input pin which, when held below 1/3 of the supply voltage, drives the output to high state. The threshold pin 6, when held higher than 2/3 of the supply voltage, drives the output to low state. By applying a low-going pulse to the reset pin 4, the output at pin 3 can be brought to the quiescent low level. Thus the reset pin 4 should be held high for normal operation of the IC.

Three sets of switches SA-SC, S1- S8 and S3-S4 are pressed, in that order, to open the lock. On pressing the switches SA and SC simultaneously, capacitor C3 charges through the potential
divider comprising resistors R3 and R4, and on releasing these two switches, capacitor C3 starts discharging through resistor R4. Capacitor C3 and resistor R4 are so selected that it takes about five seconds to fully discharge C3.

Depressing switches S1 and S8 in same time, within five seconds of releasing the switches SA and SC, pulls pin 2 to ground and IC 555 is triggered. The capacitor C1 starts charging through resistor R1. As a result, the output (pin 3) goes high for five seconds .
Within these five seconds, switches SA and SC are to be pressed momentarily once again, followed by the depression of last code-switch pair S3-S4.

These switches connect the relay to output pin 3 and the relay is energised.
The contacts of the relay close and the solenoid pulls in the latch (forming part of a lock) and the lock opens. The remaining switches are connected between reset pin 4 and ground. If any one of these switches is pressed, the IC is reset and the output goes to its quiescent low state.
The given circuit can be recoded easily by rearranging connections to the switches as desired by the user.

Stereo circuit and mono circuit are given in schematic .LA 4555 is basically a stereo amplifier with 2.3 watts into 4 ohms speakers at a total distortion of 10%. With a bridge circuit, it can be configured as mono amplifier delivering 4.6 watts. It has an input impedance of 30K and gain of 51 dB. It has an excellent voltage range of 3 to 13 volts. Both mono and stereo circuits are shown here.

Pin out is given in Figure

Input is given at Pin 8 in the mono circuit and output is taken at Pin 11 through a capacitor (C7) of 470 uF to a speaker of 4 ohms. In the case of stereo circuit, input is given at 5 and 8 pins and output is taken out at 2 and 11 pins respectively for left and right channels through the blocking capacitors C4 and C7.

A detailed description of the pin out will help now and in the future.

In the stereo circuit,

C5, C2 are feedback capacitors, zohich dictate the lower cut off frequency.

CI, C6 are bootstrap capacitors. If the capacitor value is reduced from the recommended 47uF, output

at flow frequencies falls.

Cll, CIO are oscillation blocking capacitors. Polyester film capacitors are preferable.

C7, C4 are output coupling capacitors. Lower cutoff frequency depends on their value and quality.

C3 is the ripple filter or decoupling capacitor.

C8, C9 are the power source capacitors.

R2, R2 are oscillation blocking resistors.

ICs dissipate heat as they dissipate more and more power at more and more voltages. The heat must be removed continuously such that IC operates at rated temperature. Failure to do so will result in thermal runaway. If the IC is well protected, output power will fall to a safe area. If not it will eventually fail and pack up. Copper foil area is made as large as possible in the vicinity ofIC to dissipate more heat.

Then heat sink, thermally conductive material such as copper or aluminum is mounted on IC to remove the heat as it develops. It must be of enough size. In case ofLA4555, the IC has fins which are soldered to the PCB and a small heat sink also can be soldered along with it. Solder copper heat sink as shown in the figure below. Aluminum cannot be easily soldered. Method of mounting heat sink is shown in Figure.

readmore: www.engineeringslash.com/audio-circuits/la4555-audio-amplifier.html

Motor operated stitching machines have a series of carbon buttons in an enclosure operated by foot pedal. As the pressure on the foot pedal is increased or decreased by the foot, these buttons come close or move farther away, their resistance changes and hence the speed of the motor. Even though crude, it seemed to be okay, until my wife complained.

She said that the speed is little too fast even at the minimum pressure on the foot pedal, particularly for some repair work or at embroidery. Most of the housewives also like a little more control over speed of the machine. So here you have it.

The circuit is shown in Schematic 30. This is a standard triac speed control circuit much similar to domestic fan control circuit. Contrary to other triac circuits, you will find that an additional component known as diac is used in this circuit.

Triacsfire more symmetrically when used along with diac in AC power control applications. The diac is a bidirectional trigger diode which does not conduct (except for a small leakage current) until the break over voltage is reached. Its function is designed specifically to trigger a triac or SCR.

In the beginning triac Ql is not conducting; C1 is charged through variable resistor R3. This charge is coupled to Diac through R1, R3. When trigger level of the diac is reached (about 36 V), D1 fires and Triac TR1 is switched on. R3 and C1 combination sets the firing point of the triac from zero crossing along with Rl and R2. LI and C3 combination acts radio frequency filter for the radio interference caused by triac firing.

Entire circuit operates on mains. Care must be exercised when mounting components on normal Veroboard is risky. Remove alternate tracks and mount components. Triac should be mounted on a small heat sink as the triac tends to get hot particularly at lower speeds. All capacitors are polyester or polycarbonate rated at 600V or more. Rl is a preset for minimum speed control. Adjust this according to your requirement. R2 is the linear variable resistor like the volume control in the radios. Use the one with plastic shaft. L1 is a radio interference choke. Take 28 gage winding wire and make 10 turns on a 6 mm former. It can be wound on a round capacitor for C3 and even one end can be soldered to it also.

Let’s construct a low-power FM transmitter using surface-mount devices (SMD) that will be received with a standard FM radio. Soldering surface mounted devices is not so hard and actually is quite easy. There are many designs for small FM transmitters but they have some problems. First, you need an audio amplifier to get enough modulation. Second, the antenna is attached directly to the collector.

Third, the coil L must be wound by hand and adjusted by stretching. It all ads with a weak signal that tends to drift in frequency. In contrastm the transmitter schematic we present here eliminates some of those problems, using varactor diode for tuning and modulation, givind great sensitivity without an audio amplifier.


FM Transmitter – How it works

The figure below shows the schematic of the transmitter which consists of two stages: an oscillator and an output amplifier. Modulation is from an electret microphone but you can use a low power audio source.

Oscillator stage

Transistor Q1 is a Colpitts oscillator where the frequency is determined by the parallel resonant circuit formed by inductor L, varactor V1 and capacitors C7 and C8. Q1 is a common-collector amplifier where the power gain counts. V1 is actually a dual varactor that eliminate the possibility of forward conduction at the sinewave peaks.

The frequency of oscillation is set by adjusting the DC voltage on V1 with potentiometer R2. R4 and C3 form a low-pass filter to prevent RF from feeding back onto the DC.
Capacitors C7 and C8 form an AC voltage divider to provide feedback at the emitter of Q1 to sustain oscillation. A necessary condition for oscillation to start is for the radio (C7+C8)/C7 to be sufficiently bigger than 1.

SMD transmitter circuit schematic
 

Frequency Modulation

Modulation is done by superimposing an audio signal from the electret mic onto the DC bias applied to V1. R3 and C1 form a low-pass filter to prevent RF from feeding back to the mic. R3, R4 and R2 form a votage divider for the audio.

Transmitter output stage

The output of the oscillator is fed through C9 to the Q2 emitter-follower. The output of Q2 drives the antenna through C11. The Q2 emitter-follower it ensures that the oscillator is not loaded down by the impedance of the antenna and it provides power gain to drive the antenna.

SMD Transmitter layout

The figure below shows the layout of the PCB and it uses surface-mounted devices like resistors and capacitors (non-polar devices). All the caps are size 0805 and all resistors are size 1206. use through-hole components for Q1, Q2, IC1 and V1. You can use an SOT-89 device for IC1 and an SOT-23 device for V1. Use MPSH10 or a transistor equivalent. Here you can learn how to solder smd chips


 The inductor

A coil would consist of two or three turns of wire but for this schematic we will use an inductor with loops of copper on the PCB. Such flat spiral inductor are common at these frequencies.
One formula for flat spiral inductors is:
flat spiral inductors formula where
L = inductance in uH
r = radius of coil (outer radius + inner radius divided by 2 ) inches
N = number of turns
d = depth of coil (outer radius minus inner radius) inches

Tuning range

While commercial FM band goes from about 88 MHz to 108 MHz, the L and C values used in this design allow tuning up to 100 MHz.

Transmitter testing

You will need a portable FM radio and an assistant. First, find an empty spot on the FM dial and set your radio about 30 feet away (9 meters). The radio’s volume control should not be set too high to prevend feedback. Next, power-up your transmitter and talk to yourself as you adjust the frequency with the trim-pot. When your assintant hears you, your transmitter is tuned. You might have to adjust the radio’s tuner slightly for best reception.

Have fun with it but remember that using the transmitter as a bugging device may not be legal in your country. To use the circuit as a wireless microphone, increase the value of R3. The transmitter range is about 100 feet (30 meters) inside a building.

Parts list

Heres a top-class headphone amplifier that can drive high or low impedance phones to full power levels, with very low noise and distortion. For best performance, it can be teamed with the Stereo Preamplifier described last month. Alternatively, it can be used as a standalone unit, requiring only a power supply and a volume control pot for use with any line-level signal source (CD/MP3 player etc). It even includes dual outputs, so you can listen with a friend!

Picture of the circuit:


Many of our high-power audio amplifier designs already provide an output for headphones. The additional circuitry required for headphone support is simple; just two resistors in series with the loudspeaker outputs to limit the drive current and protect the ’phones in the case of amplifier failure.

Considering its simplicity, this resistive limiting scheme works well, although it will cause distortion if the load is non-linear – a likely prospect with most headphones. Apart from eliminating this potential source of distortion, there are a number of other reasons why you might consider building a separate headphone amplifier.

For a start, not everyone owns a pair of top-rated headphones or even a high-performance power amplifier. After all, an amplifier that equals or betters the performance of this new headphone amplifier will set you back more than a few shekels!

Parts layout:


Another reason might be for use with the latest "high-tech" audio electronics gear. The headphone outputs in much of this gear cannot drive low-impedance ’phones – or at least not to decent listening levels. In addition, available output power in portable devices is deliberately limited to conserve battery energy. This means that lots of distortion might be present at higher listening levels, even with sensitive headphones.

One way around this is to feed the line-level outputs of this gear into your power amplifier and then plug your low-impedance headphones into that. That works but then you’re tethered to an immovable object. Besides, the power required to drive headphones is around 1/1000th of that required to drive loudspeakers, so a large power amplifier could be considered a tad oversized for the job!

Circuit diagram:


Main Features:

    High performance – very low noise & distortion
    Drives high and low-impedance headphones
    High output power (up to 200mW; into 8? and 32?)
    Dual headphone sockets – can drive two pairs!
    Works with a preamp or any line-level audio source

Measured Performance:

Frequency response.......................... flat from 10Hz to 20kHz (see graphs)
Rated output power........................... 200mW into 8? and 32?, 85mW into 600?
Max. output power (current or voltage limited)...............575mW into 8?, 700mW into 32?, 130mW into 600?
Harmonic distortion........................ typically .0005% (600? load),.001% (32? load) and .005% (8? load)
Signal-to-noise ratio (A-weighted)......................... -130dB (600?), -120dB (32?) and -111dB (8?) with respect to 100mW output power.
Channel crosstalk.................. better than -68dB from 20Hz-20kHz at 100m? output power (see graphs)
Input impedance.................................... ~47k? || 47pF
Output impedance..................... ~5?

Note:

All tests were performed with the amplifier driven from low source impedance. For crosstalk measurements, the non-driven input was back-terminated into 600?. 

The compact, low-cost condenser mic audio amplifier described here provides good-quality audio of 0.5 watts at 4.5 volts. It can be used as part of intercoms, walkie-talkies, low-power transmitters, and packet radio receivers. Transistors T1 and T2 form the mic preamplifier. Resistor R1 provides the necessary bias for the condenser mic while preset VR1 functions as gain control for varying its gain. In order to increase the audio power, the low-level audio output from the preamplifier stage is coupled via coupling capacitor C7 to the audio power amplifier built around BEL1895 IC.

Circuit diagram:


BEL1895 is a monolithic audio power amplifier IC designed specifically for sensitive AM radio applications that delivers 1 watt into 4 ohms at 6V power supply voltage. It exhibits low distortion and noise and operates over 3V-9V supply voltage, which makes it ideal for battery operation. A turn-on pop reduction circuit prevents thud when the power supply is switched on. Coupling capacitor C7 determines low-frequency response of the amplifier. Capacitor C9 acts as the ripple-rejection filter.

Capacitor C13 couples the output available at pin 1 to the loudspeaker. R15-C13 combination acts as the damping circuit for output oscillations. Capacitor C12 provides the boot strapping function. This circuit is suitable for low-power HAM radio transmitters to supply the necessary audio power for modulation. With simple modifications it can also be used in intercom circuits.