Simple Police Alarm Circuit

This circuit is a simple design circuit that produces an alarm similar to the police siren. This circuit is using a low and inexpensive component. This is a figure of the circuit.


How is this circuit work? When you press the push button switch S2 capacitor C1 will charge and this will make the transistor Q1 to ON slowly. When the switch S1 is released the C1 will discharge and the transistor Q1 will become OFF slowly. When the Q1 is switched ON, its collector voltage falls and makes the transistor Q2 ON. The capacitor C2 will be charged almost full supply voltage. This results in an increase in the collector-emitter voltage of Q2. This change in voltage is coupled to the base of Q1 via the capacitor C2. As a result the transistor Q1 comes slightly out of saturation. As a result the collector voltage of Q1 drops and makes the Q2 more OFF. This action continues until both transistors become OFF. Then the capacitor C2 discharges, and transistor Q1 will be switched ON again to start a new cycle. When the capacitor C1 is charged the tone will rise and when the capacitor C1 is discharging the tone will fall.

The circuit can be powered from 9V DC. Switch S1 can be used as a power ON/OFF switch. K1 can be an 8 Ohm loud speaker.

Simple Metal Detector Circuit Using Transistor

This is the design of simple circuit diagram of a low cost metal detector using a single transistor circuit and an old pocket radio. This is nothing but a Colpitts oscillator working in the medium band frequency and a radio tuned to the same frequency. This is the figure of the circuit.


Description of the circuit is following. First the radio and the circuit are placed close. Then the radio is tuned so that there is no sound from radio. In this condition the radio and the circuit will be in same frequency and same frequencies beat off to produce no sound. This is the set up. When the metal detector circuit is placed near to a metal object the inductance of its coil changes, and so do the frequency of oscillations. Now the two frequency is will be different, there will be no canceling and radio produces a hissing sound. The metal is detected. To make L1 make 60 turns of 36SWG enameled Copper wire on a 1 cm PVC tube. Powering the circuit using a adapter rather than a battery induces noise. It is always good to power radio projects from battery.

Simple High Power Alarm Circuit

This is the simple circuit of a comparatively strong siren useful for any purpose. This circuit is based on two transistor. A complementary transistor pair (BC557 & 337) is arranged as an oscillator, directly drives the peaks. The figure is shown in below.


Transistor Q1(BC 557) is used to provide full charging of capacitor C2.When P1 is pressed, C2 discharges through R8 and the circuit starts oscillating at a low frequency that increases slowly until a high frequency steady tone is reached and it is kept. When P2 is released C2 starts discharging and output frequency slowly decreases. When C2 is charged fully the circuit stops oscillations. Adjust the values of C2 & R6 to vary the tune. Wire the circuit on a good quality PCB.A good quality common board may also do trick.

Parts List.
R1, R3 1K
R2, R5 10K
R4 220R
R6 220K
R7 22K
R8 100K
C1, C2 22µF/25V
C3 10nF
C4 47µF/25V
Q1, Q2 BC557 Transistors
Q3 BC337 Transistor
SW1 SPST Toggle or Slide Switch
P1 SPST Pushbutton Switch
SPKR 8 Ohm speaker
B1 12V Battery

Simple Field Strength Meter

This is a design for simple handy field strength meter that can be used to check the strength of AM radio signals. The circuit is a very useful for those who assemble radio transmitters (especially in the tuning of the final stage for maximum range). This operation of the circuit is based on a transistor. This is the figure of the circuit.


The circuit is essentially some sort of an AM receiver it self. The capacitor C3 and inductor L1 forms a tuned circuit to receive a particular frequency (the frequency of your transmitter). The diode D1 detects the signal and applies to the base of transistor Q1 (MPSA 18). The collector current of the Q1 will be proportional to the strength of this signal and will be shown in the meter M1. In result the meter reading will be a measure of the strength of the signal (of the tuned frequency) falling on the antenna.

The C3 must be varied to tune in to the frequency of your transmitter. For that, keep the antenna of meter circuit close to the antenna of your transmitter and adjust C3 to get a maximum reading on meter M1. In order to tune your transmitter for a maximum range, place the meter circuit some place near to the transmitter and adjust the transmitters tuning elements. Maximum range setting will at the point where the meter shows full deflection. The transistor Q1 can be any high gain NPN RF transistor. Switch S1 is used as a power switch. Keep this switch OFF when circuit is not in use to save battery life. The antenna can be a 15 cm long Copper wire. Power the circuit using a 9v battery.

Simple Electromagnetic Sensor Using 741IC

This is a schematic design for the sensor to the electromagnetic field. This circuit is very simple, which is based or built by the IC 741. This IC is the op amp. The circuits that can detect even hidden field wrings. This is the schematic figures. 1mH inductor is used for electric field sensing. Small electric field will cause the voltage on the inductor and the induced voltage sensor is amplified by op amp. Headphones are connected to the output of op amp audio will an indication of electrical field. For example, the electric field around the main transformer can be heard as 50 Hz hum. The circuit figure is show in below.


In the circuit diagram is that POT can be used to adjust the gain of the amplifier. By maintaining the sensor inductor close to the phone, you can even hear the phone conversation. All electrolytic capacitors should be rated at least 15V. The switch S1 can be a slide type ON / OFF switch. R4 POT that can be used to adjust the gain. Better to have a radial type inductor.

Simple Dual Tone Train Horn Circuit Using 555 IC

This circuit a simple design for dual tone train horn simulator circuit can be made using two NE 555 timers connected in cascade. This is the figure of the circuit.


Here instead of using two NE 555 timers a single NE 556 timer is used which is a nothing but two 555 ICs in one package and each timers work independently. Switch S1 can be used to start the horn. The circuit is simple and low cost but works greatly. Use a 9V DC power supply or battery for this circuit.

Simple Brightness Control Lamps Circuit

This circuit is a simple design for brightness control lamps circuit, which is the circuit is based on 7555 IC for core operation. This is the figure of the circuit.


The operation work to control light intensity from the four filament lamp (the ring illuminator) is supported by two AA or AAA battery, for close up pictures using digital camera. The circuit will be used in another ways. The principle work of the circuit is IC1 produce 150 Hz square wave of variable duty cycle. When the cursor from P1 is fully played against D1, the output pulse appears on the positive pin 3 of IC1 is very narrow. Bulb LP1, driven by Q1, is turned off in the lead as the voltage is too low. When the cursor is played from P1 to R2, the output pulse increases in width, they reach the maximum amplitude when the potentiometer is rotated in full clockwise. In the way the bulb reaches full brightness

Part Component:
P1 = 470K Pot, R1 = 10K, R2 = 47K, R3 = 1K5, C1 = 22nF, C2 = 100uF/25V, D1/D2 = 1N4148, IC1 = 7555 or TS555CN, Q1 = BD681, LP1 =1, 5V 200mA Bulb, SW1 = SPST Switch, B1 = 3V Battery

Simple Battery Charger Circuit

This is a simple design and straight forward battery charger circuit. That circuit can be used to charge all type of 12V rechargeable batteries including car batteries. This is the figure of the circuit.


The circuit is nothing but a 12V DC power supply with an ammeter for monitoring the charging current. The two diodes forms a centre tapped full wave rectifier .The capacitor filters the rectifier output to produce a clean 12V out put. Always be careful to connect the charger to the battery in correct polarity. Positive to positive and negative to negative. When the battery is fully charged the ammeter reading will be zero. As the battery is slowly charged the current slowly decreases. At initial stages of charging the ammeter will read about 1 to 3 amperes.

Simple High Power Alarm Circuit

This is the simple circuit of a comparatively strong siren useful for any purpose. This circuit is based on two transistor. A complementary transistor pair (BC557 & 337) is arranged as an oscillator, directly drives the peaks. The figure is shown in below.


Transistor Q1(BC 557) is used to provide full charging of capacitor C2.When P1 is pressed, C2 discharges through R8 and the circuit starts oscillating at a low frequency that increases slowly until a high frequency steady tone is reached and it is kept. When P2 is released C2 starts discharging and output frequency slowly decreases. When C2 is charged fully the circuit stops oscillations. Adjust the values of C2 & R6 to vary the tune. Wire the circuit on a good quality PCB.A good quality common board may also do trick.

Parts List.
R1, R3 1K
R2, R5 10K
R4 220R
R6 220K
R7 22K
R8 100K
C1, C2 22µF/25V
C3 10nF
C4 47µF/25V
Q1, Q2 BC557 Transistors
Q3 BC337 Transistor
SW1 SPST Toggle or Slide Switch
P1 SPST Pushbutton Switch
SPKR 8 Ohm speaker
B1 12V Battery

Simple Electromagnetic Sensor Using 741IC

This is a schematic design for the sensor to the electromagnetic field. This circuit is very simple, which is based or built by the IC 741. This IC is the op amp. The circuits that can detect even hidden field wrings. This is the schematic figures. 1mH inductor is used for electric field sensing. Small electric field will cause the voltage on the inductor and the induced voltage sensor is amplified by op amp. Headphones are connected to the output of op amp audio will an indication of electrical field. For example, the electric field around the main transformer can be heard as 50 Hz hum. The circuit figure is show in below.


In the circuit diagram is that POT can be used to adjust the gain of the amplifier. By maintaining the sensor inductor close to the phone, you can even hear the phone conversation. All electrolytic capacitors should be rated at least 15V. The switch S1 can be a slide type ON / OFF switch. R4 POT that can be used to adjust the gain. Better to have a radial type inductor.

Simple Dual Tone Train Horn Circuit Using 555 IC

This circuit a simple design for dual tone train horn simulator circuit can be made using two NE 555 timers connected in cascade. This is the figure of the circuit.


Here instead of using two NE 555 timers a single NE 556 timer is used which is a nothing but two 555 ICs in one package and each timers work independently. Switch S1 can be used to start the horn. The circuit is simple and low cost but works greatly. Use a 9V DC power supply or battery for this circuit.

Simple Voltage Follower Circuit

This is a simple design for an AC coupled unity gain voltage follower operating on a single supply. This circuit is based on operation in 741 IC. This is the figure of the circuit.


The principle work of the circuit is the voltage divider network of R1 and R2 provides a DC voltage equal to half the supply voltage to the non-inverting input of the 741.The output DC voltage therefore stands at half the supply voltage. The output signal swings above and below this value. The standing DC voltage at pin 6 does not matter because the output is coupled to the next stage via a capacitor.

The input impedance is equal to the value of R1 and R2 in parallel, i.e .500K Ohms in this case. Because of hundred percents negative feedback, the output impedance is very low. For low frequency applications C1 and C2 can be replaced by electrolytic capacitors of large values. Power the circuit from a 12V battery or 12V DC power supply. The IC 741 has to be mounted on an IC holder.

Simple Voltage Booster Circuit

This is a simple circuit for boosting 12 V DC to 24 V DC. The circuit is designed straight forward and uses few components. With few modifications the circuit can be used to boost any voltages. This is a figure of the simple design circuit.


This operation of the circuit is based on the transistor Q1 and Q2 (D1616) essentially drives the primary of the transformer. The diode rectifies the output of transformer to obtain a 24V DC at the output load (here a fan).The capacitors filter away noise and harmonics away from the output. This circuit can operation with high voltage, if for high current (around 5A) games use 2N 3055 transistor or more powerful Darlington pairs for Q1 and Q2. The component values are not very specific here. We can use any NPN power transistors like D1616, 2N3055, C2236, SL100 etc for Q1 and Q2. The transformer can be any center tapped 5A transformer with a 7:1 winding ratio. The diodes can be 1N 914 ones.

Simple Touch Switch Using CD4011 IC

This is a simple design circuit for touch switch circuit. This circuit is built using CD4011 ICs. The IC CD4011 is wires as a flip flop here. This is a figure of the circuit.


This is explanation about principle work of the circuit. The 9, 13 pins of the IC works as the set and reset contacts respectively. CMOS ICs like 4011 require requires a very low current for controlling its gates. Since the pins 9 and 13 are connected to the positive via resistors R1 and R2, the logic gates of the ICs will be in high state. When we touch through the points A, B the gates of the IC will be closed and the output becomes low. This switches ON the transistor Q1 and the relay gets activated. When we touch through the points C, D the gates again becomes high and switches the transistor OFF. This makes the relay OFF. Thus by touching through the contact points A, B and C, D the appliance connected through the relay can be switched On and OFF. The relay can be a 12 V, 200 Ohm SPDT relay. The circuit is needed a power supply 12V DC for powering the operation.

Simple Start Power Supply Circuit

This is a simple circuit design of a simple soft start power supply based on IC L200.The L200 is a monolithic IC that can be used for voltage and current regulation. The built-in feature of the circuit is such as thermal shutdown, over current protection and input over voltage protection makes this IC nearly indestructible. This is a figure of the circuit.


Operation of the circuit is when the power supply to the circuit is switched ON, the capacitor C3 starts to charge through resistor R3.The internal comparator pin (pin2) of the IC is connected to the positive lead of C3. The input voltage to the IC can be anything between 18 to 40V DC. When capacitor C3 is charging the voltage at the internal comparator pin also increases. This slowly relaxes the current regulation loop inside the IC.

As a result the output voltage of the IC also slowly increase from zero to the set value of output voltage. In here the set output voltage is 15V. The IC1 must be fixed with using a heat sink. The output voltage can be set by the equation Vout = 2.77[1+ (R1/R2)]. The time duration can be set by the equation T = (R3C3/0.45)x (Vout - 0.45). The maximum current capacity of this regulator is 2A.

Simple Quartz Crystal Tester Circuit

This is a very simple and inexpensive design circuit that can be used to test quartz crystals. This circuit is using Colpitts oscillator is wired used the transistor T1. This is a figure of the circuit. For explanation the principle work of the circuit is explained in below.


When the crystal is connected between terminals A and B the circuit will produce high frequency oscillation. The oscillations will be generated only if the crystal is a good one. The diode OA91 will rectify these oscillations and it can be visually identified from the meter. The deflection of the meter will be directly proportional to the activity of the crystal.

The circuit can be powered from a 9V PP3 battery. The push button switch S1 can be used as an ON/OFF switch. The meter M1 can be a 250uA FSD ammeter. POT R5 can be used to adjust the deflection of the meter. The crystal to be tested can be connected between terminal marked A and B.

Simple Missing Pulse Detector Circuit

This is a design circuit to detecting a missing pulse. This circuit is built by NE555 timer IC connected to detect an abnormally long period between two consecutive pulses in a train of pulses, Such as circuits can be used to detect the intermittent firing of the spark plug of an automobile or to monitor the heart beat of a sick patient. This is a figure of the circuit.


Processing work of the circuit is the signal from the pick up transducer is shaped to form a negative going pulse and is applied to pin 2 of the IC which is connected as a mono stable. As long as the spacing between the pulse is less than the timing interval, the timing cycle is continuously reset by the input pulses and the capacitor is discharged via T1.A decrease in pulse frequency or a missing pulse permits completion of time interval which causes a change in the output level. The circuit can be powered from a 9V battery or 9V DC power supply. The IC1 NE555 could be mounted on a holder.

Simple Micro Ampere Meter Circuit

This is a design of simple micro ampere meter. This circuit is basically a DC milli volt meter. This is a figure of the circuit.


The circuit gives full scale deflection for 0.1V input. The current to be measured is passed through a known resistance R and the voltage drop across it is measured. This circuit is based on the IC 1 uA 741 op amplifiers wired as a non inverting amplifier. Use a +9V/-9V dual power supply for powering the circuit. The table given below shows the relationship between different values of R and the current that will give full scale deflection. The IC 1, uA 741 must be mounted on an IC base.

Simple Delayed “ON” LED Circuit

This is a very simple design of circuit in which the LED becomes ON only after a preset time the power supply is switched ON. This circuit is consist of low price component. This is the figure of the circuit.


Principle work of the circuit is when the power supply is switched on the transistor will be OFF. The capacitor now charges via the preset R3 and when the voltage across C1 is sufficient, the transistor switches ON and LED glows. The ON delay depends on the value of POT R3 .You can increase the time delay by increasing the resistance of POT R3. The circuit can be powered from a 10V DC power supply. Anyway you can use from 6 to 18V for powering this cicuit, but you need to adjust the POT R3 for getting the required delay.

This circuit alone may not have much practical applications but this can be used in many other projects where a delayed ON indication is required.

Simple VHF Strength Meter Circuit

This is a circuit for VHF strength measurement devices. This design is very simple for built. The field strength is measured by converting the radio signal to DC and measuring it. This is the figure of the design circuit.


Operation of the circuit is RF signal will be picked up by the coil and rectified by the diode D1.Even a very small DC voltage is sufficient to alter the biasing of FET and it will be reflected in the meter as an indication of the presence of a radio signal. The meter can be calibrated by adjusting the preset R2 to make meter M1 read ZERO in the absence of any radio signal. This circuit is not very sensitive, but can sense radio signals from hand held FM transmitters up to a distance of few meters (ideal for theoretical demonstrations).

The coil L1 can be made by making 6 turns of 20 SWG enameled copper wire on a ¼ inch plastic former. The antenna for this circuit can be a telescopic whip antenna. Use a 250uA FSD current meter for M1.Using a lower FSD meter will improve sensitivity. Use a 9V PP3 battery for powering the circuit.

Simple Main Failure Alarm Circuit Using Transistor

This is a simple mains failure alarm circuit that produces an alarm whenever the mains supply fails. Lot of such circuits are available, but the peculiarity of this circuit is that it requires no back up power source like a battery to power the alarm when the mains is absent. This circuit is built by a transistor BC558. This is a figure of the circuit.


This is operation of the circuit. When there is mains supply the transistor Q1 (BC558) will be OFF and the capacitor C1 will be charged. You can use any general purpose PNP transistor (like BC158, BC177 etc) as Q1. When the mains supply fails the transistor Q1 becomes ON and the capacitor C1 discharges through the Q1 to drive the buzzer to produce an alarm. T1 can be a 230V primary, 6V secondary, 500mA transformer. The capacitor C2 is the filter capacitor for the bridge. All capacitors are rated 25V. Diode D2 prevents the discharge of the C2 when main fails. If D2 is not there, the alarms will remain silent for a time capacitor C2 to fully discharge after the power failure. B1 can be a 1A bridge. You can make the same using four 1N 4007 diodes.

Simple Blown Fuse Indicator Circuit

This is a simple design circuit for adding a blown fuse indicator to your existing power supply circuit. This is done by just adding a resistor and LED to the existing circuit. The LED and resistor are connected in series and this combination is connected in parallel to the existing fuse. This is the figure of the circuit.


Operation the circuit is when the fuse is intact, it offers a low resistance and so the voltage drop across it will be not sufficient enough to glow the LED. When the fuse is blown off, it is equivalent to infinite resistance and so the entire power supply will drop across the resistor LED series combination and makes the LED glow. The resistance R1 is used to limit the current through LED.

The component values of other components are not given in the diagram because it depends on your specific power supply requirements. Any way for a conventional 12V power supply the component values are as follows: 1N4007 for D1,D2,D3 and D4; 230V primary,12V secondary ,2A step-down transformer for T1, 2A fuse and a 1000uF/25V capacitor for C1. The circuit will not work if the load is not connected. A highly resistive load may also impart the working of the circuit. The components for this circuit can easily obtained from your electronic junk box.

Simple Air Flow Detector Circuit Using LM339

This is a design for detecting air flow. This circuit can give visual for the measurement. It can be also used to check whether there is air flow in a given space. This is the figure of the circuit.


This circuit is built using LM339 IC. The filament of an incandescent bulb is the sensing part of the circuit. The filament L1 can be made by removing the glass of a 40W incandescent bulb. The circuit can be powered from a 12 V DC power supply. Operation of the circuit is when there is no air flow the resistance of the filament will be low. When there is air flow the resistance drops, because the moving air will remove some of the heat generated in the filament. This variation in the resistance will produce variation of voltage across the filament. These variations will be picked up by the op amp (LM339) and the brightness of the LED at its output will be varied proportionally to the airflow.

Simple Water Level Alarm Circuit

This is a simple design for water level alarm that will produce an audible alarm when the water level reaches a preset level. The circuit can be powered of a 3V battery and is very handy to use. This is the figure of the circuit water level alarm.


The operation of the circuit is based on an multi vibrator wired around IC1 (NE 555).The operating frequency of the unstable multi vibrator here will depend on capacitor C1, resistances R1,R2 and the resistance across the probes A&B. When there is no water up to the probes, they will be open and so the multi vibrator will not produce oscillations and the buzzer will not beep. When there is water up to the level of probes, some current will pass through the water, the circuit will be closed to some extend, and the IC will start producing oscillations in a frequency proportional to the value of C1, R1, R2 and the resistance of water across the probes. The buzzer will beep to indicate the presence of water up to the level of the sensing probes. The probes can be made of two insulated copper Aluminum wires and place the probes at the position where you have to sense the level. The power supply for this sensor is 3 V from battery.

Simple Telephone Transmitter Circuit Using Transistor

This is a simple circuit for telephone transmitter. This circuit is ideal for transmitting the telephone conversation through small distances. The circuit using a few components to setup the circuit and its based on a transistor as core the circuit. This is a figure of the circuit.


In the entire of the circuit can be included in the telephone itself or in the junction box. The power supply of the circuit is from the telephone line. The operation of the circuit is the transistor is wired as a Colpitts oscillator to produce oscillations in the FM transmission band. The audio signal from the telephone line is coupled to the base of the transistor to obtain the frequency modulation. The LED D1 is act as a power on indicator. Any radio frequency PNP transistor like A933 can be used for built the transistor. For L1 make 8 turns of 0.6 mm diameter enameled copper wire on a 3.6mm diameter steel bolt and the antenna use a 15 cm long 0.6 mm diameter copper wire.

Simple Speaker – Microphone Converter

This is a simple schematic that can be used for converting audio signal. The function of the circuit is approach for converting a loud speaker into a microphone. This circuit is based on transistor for convert the signal. This is the figure of the circuit.


The operation of the circuit is when the sound waves fall on the diaphragm of a speaker, there will be fluctuations in the coil and there will be a small proportional induced voltage. Usually this induced voltage is very low in magnitude and useless. Here in the circuit the low voltage is amplified using transistors to produce a reasonable output. The transistor Q1 is wired in common base mode and produces the required voltage gain. The transistor Q2 is wired as an emitter follower to produce enough current gain. The voice quality of this circuit will not be as much as a conventional microphone but quite reasonable quality can be obtained. To set up the circuit, keep the preset R2 at around 10 Ohms and connect the battery. Now adjust R2 to obtain the optimum sound quality.

Simple Regulator Power Supply 9V using LM7809

This is a simple design for power supply that built by LM7809 IC. This power supply is kind of regulator power supply that can supply 9V DC voltage. This figure is the circuit of power supply;


The LM7809 is a 9V voltage regulator IC with features such as internal current limit, safe area protection, thermal protection etc. A current of 300 mA or above is required ,fit a proper heat sink to the IC 7809. 1A bridge is not available, make one using four 1N 4007 diodes.

Simple IR Audio Transmitter Circuit

This is a simple design for infra red audio link that can be used as transmit audio signals up to 4 m. The circuit is based on 3 transistor and one photo transistor. The photo transistor Q2 can be any NPN photo transistor like PNZ154, PNA1605F, BPW77NA or BPW85. And the transistor is using BC548. This is the figure of the complete circuit of the simple IR Audio Transmitter circuit.


Operation of the circuit the signal to be transmitted is applied to the base of Q1 via resistor R4. The transistor Q1 drives the IR transmitting diodes D1 and D2. The audio input will be modulated to the IR signals transmitted. The transmitted IR signals will be picked by the photo transistor Q2. The emitter voltage of the transistor Q2 will change according to the sound modulated to the IR signal. The transistor Q3 and Q4 amplifies this signal to drive the speaker or headphone. C1 and R3 form a filter to avoid interference from stray IR signals. For power supply, this circuit is use 9V PP3 batteries for powering the transmitter and receiver. An 8 Ohm speaker or a headphone can be used to hear the sound.

Simple 24W Amplifier Using IC

This is a simple design for power amplifier. This circuit is can produce amplifier 24 W mono. It is built by TDA1516 IC. This IC is an IC type B for power amplifier. This is the figure of the circuit.


Operation of this circuit is the IC has many useful features such as short circuit protection, load dump protection, thermal protection, reverse polarity protection etc. Here the IC is wired in BTL mode to deliver 24W of power into a 4 ohm speaker. This amplifier can be operated from a 12V DC supply and this makes it suitable for car audio applications. The amplifier can be powered using a 12V DC supply. Capacitor C2 must be rated at least 25V. The IC must be fitted with a heat sink. Switch S1 is the stand by switch.

Simple Power Supply Using L200 IC

This is the circuit diagram of a simple soft start power supply using the well known IC L200. The L200 is a monolithic IC that can be used for voltage and current regulation. The built-in features such as thermal shut downs, over current protection and input over voltage protection makes this IC nearly indestructible. This is a figure of the circuit;


The operation of the power supply is when the power supply to the circuit is switched ON, the capacitor C3 starts to charge through resistor R3.The internal comparator pin (pin2) of the IC is connected to the positive lead of C3.When capacitor C3 is charging the voltage at the internal comparator pin also increases. This slowly relaxes the current regulation loop inside the IC .As a result the output voltage of the IC also slowly increase from zero to the set value of output voltage. Here the set output voltage is 15V. The power supply can assembly the circuit on a good quality PCB. The input voltage to the IC can be anything between 18 to 40V DC. The IC1 must be fixed with a heat sink. The maximum current capacity of this regulator is 2A.

Simple 2W Amplifier Using TDA 7052

That is a simple design circuit for power amplifier. It is suitable for small pocket radios and other portable audio gadgets. The circuit is based on Phillips Semiconductors IC TDA 7052. This makes it ideal for battery operated gadgets. The IC TDA7052 is a mono output amplifier coming in 8-lead DI package (DIP). The device is mainly designed for battery-operated portable audio circuits. The features of TDA 7052 include ,no external components needed, no switch-on or switch-off click sounds , great overall stability ,very low power consumption(quiescent current 4mA) , low THD, no heat sinks required and short-circuit proof. This is the figure of the circuit;


The work of the amplifier is the gain of TDA 7052 is fixed internally at 40 dB. It is to compensate the reduction of output power due to low voltage supply the TDA7052 uses the Bridge-Tied-Load principle (BTL) which can provide an output of around 1 to 2 W Rms (THD = 10%) into an 8 Ohm load with a power supply of 6 V.

In the circuit the potentiometer can be used to control the volume. Capacitor C1 and C2 are meant for filtering the supply voltage if a battery eliminator is used as supply source. For operations using a battery C1 and C2 are no necessary.

Simple 1.3V Power supply Circuit

This is a simple design of power supply that can be used as replacement for the 1.3V Mercury Cell in any circuit. This component for the circuit is only need some component like resistor, capacitor, diode. This is a figure for the circuit.


The operation of the circuit is when the input 5V is given to the circuit, the voltage drop across zener diode D1 will be around 2V.The diode D2 will drop a 0.7 V from the 2V volt and the remaining 1.3V will be available at the output. The Resistor R1 limits the current through zener diode. There are some attention for the circuit. The circuit can be assembled on a general purpose board. This power supply is suitable for measurement devices like digital multi meters, digital clocks, digital thermometers etc. The zener diode D1 can be a 2V one like BZX552V0.

Simple AM Transmitter Circuit

This is a simple design for AM transmitter radio. It is illegal to operate a radio transmitter without a license in most countries. This circuit is deliberately limited in power output but will provide amplitude modulation (AM) of voice over the medium wave band. The figure is the complete circuit;


The description of the circuit is the circuit is in two half, an audio amplifier and an RF oscillator. The oscillator is built around Q1 and associated components. The tank circuit L1 and VC1 is tunable from about 500 kHz to 1600 KHz. These components can be used from an old MW radio, if available. Q1 needs regenerative feedback to oscillate and this is achieved by connecting the base and collector of Q1 to opposite ends of the tank circuit. The 1nF capacitor C7, couples signals from the base to the top of L1, and C2, 100pF ensures that the oscillation is passed from collector, to the emitter, and via the internal base emitter resistance of the transistor, back to the base again. Resistor R2 has an important role in this circuit. It ensures that the oscillation will not be shunted to ground via the very low internal emitter resistance, re of Q1, and also increases the input impedance so that the modulation signal will not be shunted. Oscillation frequency is adjusted with VC1.

Q2 is wired as a common emitter amplifier, C5 decoupling the emitter resistor and realizing full gain of this stage. The microphone is an electric condenser microphone and the amount of AM modulation is adjusted with the 4.7k preset resistor P1. An antenna is not needed, but 30cm of wire may be used at the collector to increase transmitter range.

Simple 22 Watt Audio Amplifier Circuit

This circuit is a simple design for power amplifier. The power amplifier has output 22W. This circuit is easy to build and low cost. The circuit can be used as a booster in a car audio system, an amp for satellite speakers in a surround sound or home theater system, or as an amp for computer speakers. The circuit is quite compact and uses only about 60 watts. The figure is the circuit of the power amplifier;


The circuit works best with 4 ohm speakers, but 8 ohm units will do. The circuit dissipates roughly 28 watts of heat, so a good heat sink is necessary. The chip should run cool enough to touch with the proper heat sink installed. The circuit operates at 12 Volts at about 5 Amps at full volume. Lower volumes use less current, and therefore produce less heat. Printed circuit board is preferred, but universal solder or perfect board will do. Keep lead length short.

This is a part of the component;
R1 39K 1/4 Watt Resistor
C1, C2 10uf 25V Electrolytic Capacitor
C3 100uf 25V Electrolytic Capacitor
C4 47uf 25V Electrolytic Capacitor
C5 0.1uf 25V Ceramic Capacitor
C6 2200uf 25V Electrolytic Capacitor
U1 TDA1554 Two Channel Audio Amp Chip
MISC Heat sink For U1, Binding Posts (For Output), RCA Jacks (For Input), Wire, Board

Simple 3 Band Equalizer Circuit

This is a simple design schematic for equalizer. The principle of the circuit is using a tone control. There are three ranges, basses, middle and treble in single op-amp that can be control. This is a figure of the circuit.


This circuit is using a single op-amp this easy to make equalizer offers three ranges, low frequency, mid frequency, and high frequency. The op-amp is based on LF351 IC with component values shown there is approximately +/-20dB of boost or cut at frequencies of 50Hz, 1kHz and 10kHz. Supply voltage may be anything from 6 to 30 Volts. Maximum boost 20dB is only realized with maximum supply voltage of 18 Volt.

20W Audio Power Amplifier Circuit

This is a simple design for power amplifier. This circuit is based on an IC that is LM1875. The LM1875 is a monolithic power amplifier offering very low distortion and high quality performance for consumer audio applications. The figure of the circuit is;


The feature of the power amplifier is producing 20 W Up to 30 W output power. AVO typically 90 dB. Low distortion: 0.015%, 1 kHz, 20 W. Wide power bandwidth: 70 kHz. It having protection for AC and DC short circuits to ground. Thermal protection with parole circuit. High current capability: 4A. Wide supply range 16V-60V. Internal output protection diodes. 94 dB ripple rejection.