Personal Alarm using IC 74HC04

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This circuit uses digital CMOS IC 74HC04 used power supply 3V only. The IC perform produce the

frequency about 2.8kHz and 3.3kHz work can alternate into pieces warn to follow want.

These handheld piezo screamers are also known as rape alarms. They are a very loud siren. This one is

particularly loud even though it runs on only two AA batteries. It uses a push-pull transformer output.

The detail is other , see in circuit picture.

Source:

http://www.members.shaw.ca/novotill/PersonalAlarms/index.htmMore Electronics KIT power by Amazon.com 

Soft Start for power supply units

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The circuit will limit the current through the supply wires to 5.5A for about 1.5sec. After that time the relay

will close and the current flow won’t be restricted anymore. This is a very interesting circuit if you have a

large toroid with big electrolytic caps connected to the power supply, since these will act like short circuits

for a small amount of time if they start charging

Read more original source:

http://mitglied.lycos.de/Promitheus/delay_circuit_for_toroids.htm

Digital Voice Record and Playback Project by ISD2560P

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This project is based on ISD2560P IC which allows us to record 60 seconds voice and playback it with

very high quality. As shown in the schematic, we input the voice by using an electret microphone. If a

dynamic microphone is used, R2,R3,R4 resistors and C3,C5,C7 capacitors will be omitted and

microphone will be connected to 17 and 18 numbered pins directly. Since it has better frequency

response, we choose electret microphone in this project.

Digital Voice Record and Playback Circuit Schematic Controlling the circuit is very simple. Sw1 switches

between record and playback modes. Push button B1 is used for start and pause functions. B2 stops the

process.

To record voice, first move Sw1 to record position and push B1 once. IC will start recording and during

this process red LED will bright. One push to B1 pauses and second push continues recording. You can

record 60 seconds by this way. To stop recording push B2.

To listen the voice recorded before, move Sw1 to playback position then push B1. During the playback

process red LED will bright again. One push to B1 pauses and second push continues playing. To stop

playback push B2.

Related Links Circuits

More digital circuit

More about Voice Record

More circuit about audio article  

Voice Record / Playback Circuit

Telephone Record Control

Read More Source:

http://www.circuit-projects.com/

digital-voice-record-and-playback-project-by-isd2560p.html

Thank you.

Audio Amplifiers

Modest power audio amplifiers for driving small speakers or other light loads can be constructed in a number of ways. The first choice is usually an integrated circuit designed for the purpose.  A typical assortment can be seen on this National Semiconductor page. Discrete designs can also be built with readily available transistors or op-amps and many designs are featured in manufacturers' application notes. Older designs employed audio interstage and output transformers but the cost and size of these parts has made them all but disappear. (Actually, when the power source is a 9 volt battery, a push-pull output stage using a 500 ohm to 8 ohm transformer is more efficient than non-transformer designs when providing 100 milliwatts of audio.) As a general rule, transformerless low power speaker projects will work better with 4.5 or 6 volt battery packs of AA, C, or even D cells than 9 volt rectangulars.

Here are a few easy-to-build audio amplifier circuits for a variety of hobby applications:

Simple LM386 Audio Amplifier Computer Audio Booster

4-Transistor Amplifier for Small Speaker Applications

Op-Amp Audio Amplifier

Crystal Radio (and other purpose) Audio Amplifier

Class-A Audio Amplifiers

Simple LM386 Audio Amplifier

This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a maximum gain of only 20, leave out the 10 uF connected from pin 1 to pin 8. Maximum gains between 20 and 200 may be realized by adding a selected resistor in series with the same 10 uF capacitor. The 10k potentiometer will give the amplifier a variable gain from zero up to the maximum.

Computer Audio Booster

Here is a simple amplifier for boosting the audio level from low-power sound cards or other audio sources driving small speakers like toys or small transistor radios. The circuit will deliver about 2 watts as shown.  The parts are not critical and substitutions will usually work.  The two 2.2 ohm resistors may be replaced with one 3.9 ohm resistor in either emitter.

4-Transistor Amplifier for Small Speaker Applications

The circuit above shows a 4-transistor utility amplifier suitable for a variety of projects including receivers, intercoms, microphones, telephone pick-up coils, and general audio monitoring. The amplifier has a power isolation circuit and bandwidth limiting to reduce oscillations and "motorboating". The values are not particularly critical and modest deviations from the indicated values will not significantly degrade the performance.

Three cell battery packs giving about 4.5 volts are recommended for most transformerless audio amplifiers driving small 8 ohm speakers. The battery life will be considerably longer than a 9 volt rectangular battery and the cell resistance will remain lower over the life of the battery resulting in less distortion and stability problems.

The amplifier may be modified to work with a 9 volt battery if desired by moving the output transistors' bias point. Lowering the 33k resistor connected from the second transistor's base to ground to about 10k will move the voltage on the output electrolytic capacitor to about 1/2 the supply voltage. This bias change gives more signal swing before clipping occurs and this change is not necessary if the volume is adequate.

As before, the two 4.7 ohm resistors may be replaced with a single 10 ohm resistor in series with either emitter.

Op-Amp Audio Amplifier

The above circuit is a versatile audio amplifier employing a low cost LM358 op-amp. The differential inputs give the amplifier excellent immunity to common-mode signals which are a common cause of amplifier instability. The dotted ground connection represents the wiring in a typical project illustrating how the ground sensing input can be connected to the ground at the source of the audio instead of at the amplifier where high currents are present. If the source is a power supply referenced signal then one of the amplifier inputs is connected to the positive supply. For example, an NPN common-emitter preamplifier may be added for very high gain and by connecting the differential inputs across the collector resistor instead of from collector to ground, destabilizing feedback via the power supply is greatly reduced.

My utility amplifier was built into an aluminum Bud box and eventually ended up bolted to the bottom of a shelf as shown. The well-behaved and ready-to-go amplifier is really handy.

As is often the case, the circuit values are not critical. Other op-amps will usually work but a bit of experience may be necessary if problems develop. The two 4.7 ohm resistors in the emitters may be replaced with a single 10 ohm resistor in either position - I just like the symmetry!

Crystal Radio (and other purpose) Audio Amplifier

Here is a simple audio amplifier using a TL431 shunt regulator. The amplifier will provide room-filling volume from an ordinary crystal radio outfitted with a long-wire antenna and good ground. The circuitry is similar in complexity to a simple one-transistor radio but the performance is superior (with the exception of the amazing one-transistor reflex ). The TL431 is available in a TO-92 package and it looks like an ordinary transistor so your hobbyist friends will be impressed by the volume you are getting with only one transistor and the amplifier may be used for other projects, too. Higher impedance headphones and speakers may also be used. An earphone from an old telephone will give ear-splitting volume and great sensitivity! The 68 ohm resistor may be increased to several hundred ohms when using high impedance earphones to save battery power.

Here is the amplifier used to boost the output from a simple crystal radio. The volume control is at the bottom left and the other components are on the terminal strip at the bottom of the picture. This is a really quick and easy audio amplifier!

Class-A Audio Amplifiers

A class-A audio amplifier is pretty wasteful of power but when plenty of power is available the simplicity is attractive. Here is a simple darlington transistor example intended for use with a 5 volt power supply:

This circuit and the following aren't for beginners; they are of limited usefulness and require an understanding of the underlying principles

and potential applications. They all pass DC through the speaker

which is wasteful and can cause problems for the inexperienced builder. If built without variation, they should perform as described

but make sure to read the text.

The 5 volts should be provided by a regulated power supply. The efficiency is below 25% and significant DC current flows in the speaker and that additional power should be figured in to the power rating of the speaker. But look how simple it is! The voltage gain is only about 20 and the input impedance is about 12k. The schematic shows two values of bias resistor to be used with the corresponding speaker impedance. With the 150k bias resistor and 8 ohm speaker, the circuit draws about 210mA (1 watt) and can deliver about 250 mW to the speaker which is plenty of volume for most small projects.   The speaker should be rated at 500 mW or more and should exhibit a DC resistance near 8 ohms (perhaps 7 ohms). Check the candidate speaker with an ohmmeter; much below 7 ohms will cause excessive current draw. With the 220k resistor and 16 ohm speaker, the circuit draws about 100 mA (500 mW) and delivers about 125 mW to the speaker. The 16 ohms speaker should be rated at 200 mW or more and exhibit nearly 16 ohms of DC resistance. (Most small speakers have a DC resistance near the rated impedance and that resistance is used to set the quiescent current level in this circuit.) Other NPN darlington transistors will work but choose one that can dissipate 1 watt minimum. Most power types don't need a heatsink but tiny TO92's might overheat.

If the inefficiency of the class-A hasn't dissuaded you yet, here is a 4-transistor amplifier suitable for small signals:

 

The input impedance is about 5000 ohms and the frequency response is flat from 30 Hz to over 20,000 Hz. With the 8 ohm speaker the current drain is about 215 mA and the gain is about 1700 (64 dB). With the 16 ohm speaker the current gain is about 110 mA and the gain is about 2500 (68 dB).  A volume control may be added by connecting one end of a 5k potentiometer to ground, the wiper to the amplifier input. The other end of the pot becomes the input.

Lets face it; just about any of the various IC audio amplifiers make more sense than this inefficient design. But, this circuit uses parts with only 3 legs. Umm, it doesn't use large capacitors except for the power supply bypassing. Lets see, its more fun-ariffic.  Well, lets see if we can come up with a project that takes advantage of the inefficiency:

So, what is it?

It is a modulated light sender! Connect the input to an audio source or microphone (a speaker will work) and the audio will amplitude modulate the light intensity. The inefficiency of the class-A works in our favor now, lighting the lamp to mid-brightness with no audio present. Actually, with a 4.7 volt bulb, the lamp will be near full brightness and will be "overdriven" on sound peaks. A higher voltage bulb will last longer but will be dimmer. Try a 6.8 volt bulb as a compromise. With a sensitive detector like a phototransistor, this communicator will work several hundred feet (at night). Best range is realized if the bulb is mounted in a typical flashlight reflector and the detector is similarly mounted. The input capacitor is reduced to .01 uF to give the amplifier a high-pass character to compensate for the slow response of the bulb. The audio will sound a bit muffled, anyway. The clever designer could use this amplifier for the receiver, too, switching the speaker to the input for transmitting and to the output for listening. If you choose a detector with good infrared response, like a pin photo diode, you can add

plastic IR filters to block out ambient light and make the communicator harder to see at night.

Increasing the voltage to 12 VDC, replacing the bulb with a  3 watt, 16 ohm speaker and replacing the .01uF with a 1uF gives an audio amp that will deliver nearly 1 watt of audio power. The speaker will get warm, however! (Due to the nearly 2 watts of DC power in the speaker coil.)

Simple fire alarm circuit using IC timer NE555

Here the simple file alarm circuit based timer ID NE555. The works is simple, the lamp give light to the LDR (Light

Depending Resistor) as light sensor. When the light from the lamp covered with smoke then the LDR will change its

resistance value and then activated the alarm.

The thermistor offers a low resistance at high temperature and high resistance at low imperature. This phenomenon is

employed here for sensing the fire.

The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The

output(pin 3) of IC1 is couples to base of transistor T3(SL100), which drives the speaker to generate alarm sound. The

frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2.When thermistor becomes hot, it

gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2.

Capacitor C1 charges up to the positive supply voltage and increases the the time for which the alarm is ON. The larger the

value of C1, the larger the positive bias applied to the base of transistor T1 (BC548). As the collector of T1 is coupled to the

base of transistor T2, the transistor T2 provides a positive voltage to pin 4 (reset) of IC1 (NE555). Resistor R4 is selected s0

that NE555 keeps inactive in the absence of the positive voltage. Diode D1 stops discharging of capacitor C1 when the

thermistor is in connection with the positive supply voltage cools out and provides a high resistance path. It also inhibits the

forward biasing of transistor T1.

posted by schematic diagram at 5:07 pm

labels: alarm

7W Amplifier with TDA2003 audio circuit

Here the schematic diagram of 7W audio amplifier based on IC TDA2003.

Download 7W Amplifier with TDA2003 audio circuit in PDF version HERE

Labels: amplifier circuits

Posted by schematic diagram at 7:06 PM 0 comments

Sunday, August 23, 2009

Pre-amp circuit with tone control

This a 2 in 1 circuit where 2 modules joined in one circuit. With this circuit, you no longer use tone control

circuit before your amplifier, but you can add an equalizer between this circuit and your amplifier circuit.

In this circuit, P1 is used to control the volume level, P2 to control Bass level and P3 controls Treble level.

This is a mono channel circuit, you need to build another equal circuit to make thiscircuit has stereo

channel.

Part List:

R1__________220K 1/4W Resistor

R2__________100K 1/4W Resistor

R3__________2K7 1/4W Resistor

R4,R5_______8K2 1/4W Resistors

R6__________4K7 1/4W Resistor

R7,R8,R13___2K2 1/4W Resistors

R9__________2M2 1/4W Resistor

R10,R11_____47K 1/4W Resistor

R12_________33K 1/4W Resistor

R14_________470R 1/4W Resistor

R15_________10K 1/4W Resistor

R16_________3K3 1/4W Resistor (See Notes)

C1,C2,C9____470nF 63V Polyester Capacitors

C3,C4_______47nF 63V Polyester Capacitors

C5,C6_______6n8 63V Polyester Capacitors

C7__________10µF 63V Electrolytic Capacitor

C8,C10______22µF 25V Electrolytic Capacitors

C11_________470µF 25V Electrolytic Capacitor

Q1,Q3_______BC550C 45V 100mA Low noise High gain NPN Transistors

Q2__________2N3819 General-purpose N-Channel FET

Labels: mic preamplifier, tone control circuits

Posted by schematic diagram at 8:16 PM 0 comments

Monday, August 17, 2009

Amplifier Power Indicator

This is one of many audio level indicator circuit. The different is that this circuitshould be connected tho

the output of amplifier while the other indicators connected before amplifier module. This circuit will show

the real audio output by LED indicator level.

R1_____________220R 1/2W Resistor

R2,R5,R6,R8____100R 1/4W Resistors

R10,R12,R14____100R 1/4W Resistors

R3_____________220R 1/4W Resistor

R4,R7__________330R 1/2W Resistors

R9_____________560R 1/2W Resistor

R11____________820R 1/2W Resistor

R13______________1K2 1/2W Resistor

D1___________1N4004 400V 1A Diode

D2,D4,D6__BZX79C2V7 2.7V 500mW Zener Diodes

D3,D5,D7,D8,D9,D10 Red LEDs (Any dimension and shape) (See Notes)

Notes:

The output power indicated by each LED must be doubled when 4 Ohms loads are driven.

The circuit can be adapted to suit less powerful amplifiers by reducing the number of LEDs and

related voltage dividers.

LEDs of any dimension can be used, but rectangular shaped devices will be more suitable to be

compacted in bars or columns.

For a stereo amplifier, two identical circuits are required.

Labels: audio level meter

Posted by schematic diagram at 7:58 PM 0 comments

Wednesday, August 12, 2009

8W Amplifier Based on IC LM383

This is the 8W audio amplifier with IC LM383 as the main component. Very simple, easy and

cheap circuit.

Component part list:

C1 - 10uf Electrolytic Capacitor

C2 - 470uf Electrolytic Capacitor

C3 - 0.1uF Disc Capacitor

C4 - 2000uf Electrolytic Capacitor 2200uF

R1 - 2.2 Ohm Resistance (Anything Within 10% tolerance)

R3 - 220 Ohm Resistance (Anything Within 10% tolerance)

IC1 - LM383 IC

Labels: amplifier circuits

Posted by schematic diagram at 3:39 AM 0 comments

Wednesday, August 5, 2009

Audio Level Meter with 8 LEDs Indicator

This audio level meter required 2 pieces of LM324 for each channel. Every single LM324 contain 4 op-

amps, then you need 2 pieces of LM324 to cover 8 LEDs. And need 4 piece of LM324 for 16 LEDs (for

stereo channel)

Here the schematic:

Labels: audio level meter

Posted by schematic diagram at 6:53 PM 0 comments

Monday, July 27, 2009

2W MiniBox Audio Amplifier

This circuit is simple and cheap, the components also easy to find. This amplifiercan be feed by MP3

Player, MP4 Player, Walkman, Mini-Disc, iPod and CD players, computers and similar devices fitted with

line or headphone output.

Component parts:

P1_____________10K Log.Potentiometer

R1,R2__________33K

R3_____________33R

R4_____________15K

R5,R6___________1K

R7____________680R

R8____________120R

R9____________100R 1/2W Trimmer Cermet

C1,C2__________10µF 63V Electrolytic Capacitors

C3____________100µF 25V Electrolytic Capacitor

C4,C7_________470µF 25V Electrolytic Capacitors

C5_____________47pF 63V Ceramic Capacitor

C6____________220nF 63V Polyester Capacitor

C8___________1000µF 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

Notes:

The amplifier(s) can be conveniently supplied by a 12V wall plug-in adapter.

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.

Labels: amplifier circuits

Posted by schematic diagram at 8:57 PM 0 comments

Mini Audio Mixer circuit

This is simple mini audio mixer. This circuit consume low current due to the simple design. Also

featuring three inputs with switchable high/low sensitivity and unusual level-control circuits, providing high

overload margins and low-noise figures, proportional to gain-level settings.

Component parts:

P1,P2,P3_________5K Linear Potentiometers

R1,R11,R15_____180K

R2,R12,R16_______2M2

R3,R13,R17_____750R (See Notes)

R4,R14,R18_______1K

R5______________15K

R6_____________220R

R7_______________1K5

R8_____________820R

R9_____________150R

R10____________100K

C1,C6,C8_________1µF 63V Polyester or Electrolytic Capacitors

C2,C4,C7,C9____100µF 25V Electrolytic Capacitors

C3,C5__________220µF 25V Electrolytic Capacitors

Q1,Q4,Q5______BC550C 45V 100mA Low noise High gain NPN Transistors

Q2____________BC547 45V 100mA General purpose NPN Transistor

Q3____________BC557 45V 100mA General purpose PNP Transistor

J1,J2,J3________3mm or 6mm Mono Jack sockets

SW1,2,3,4______SPST Toggle or Slider Switches

B1_______________9V PP3 Battery

Clip for PP3 Battery

Notes:

When SW1, SW2 or SW3 are open the input sensitivity is suited to high-output devices like CD

players, tuners, tape recorders, iPods, miniDisc players, computer audio outputs etc.

When SW1, SW2 or SW3 are closed the input sensitivity is suited to low-output, low-impedance

moving coil or electret microphones.

Sometimes, the 750 Ohm value for R3, R13 and R17 resistors could be not easy to find. In this

case, two 1K5 resistors wired in parallel can be used to replace each item.

To make a stereo mixer, all the parts must be doubled excepting R6, C3, C5, SW4 and B1.

Labels: mixer circuits

Posted by schematic diagram at 8:32 PM 0 comments

wednesday, january 21, 2009

50W Audio Amplifier

About the schematic diagram:

The circuit is designed such that most of the components are not critical and can be easily replaced by nearest values.This

make it ideal to assemble from your electronicsjunk box.

The capacitor C1 controls low frequencies and capacitor   C2 controls high frequencies.The circuit ia basically a class B

amplifier.The transistors 2N 3055 serves the function of driving the speaker.The other transistor functions as pre amplifiers

for the driver stage.This is the basic scheme of the circuit.The maximum power level of amplifier can be set by adjusting the

500 Ohm POT connected with the BC107 transistor.

Notes:

The circuit can be powered using a 50 V DC power supply with 5A current rating.Up to 60 v can be given to the

circuit.Any way the power supply must be well regulated and filters to avoid noise.

Adjust the 500 ohm POT to obtain optimum performance.

All capacitors must be rated higher than the supply voltage.

Volume control can be attained by connecting a 10 K POT in series to the input of the amplifier.(Not shown in

circuit).