GPS Locked Frequency Standard Circuit Diagram

Imagine that one day you wake up to learn that all the GPS satellites have been destroyed. What's happening? War? Super-massive solar flare? Whatever it is you probably won't be spending the afternoon in your electronics hobby area. In all my years of playing with GPS it has never been "off the air." So, as a hobbyist, do you really need a GPS standard with "hold-over" that learns the properties of your oscillator and corrects the oscillator even when GPS is not present? (Hint: nope.) So why spend an inordinate amount of time and effort giving your standard a hold-over function you can only appreciate by physically disconnecting the GPS antenna?

This unit provides an excellent 10 MHz reference as long as an accurate 1PPs is supplied by the GPS receiver. When GPS goes down you should be brushing up on your hunter-gatherer skills anyway.

This simple frequency standard uses the 1PPS available from many GPS receivers to lock a stable oven-controlled oscillator, holding a few hundred uHz of accuracy from moment to moment depending on the quality of the oscillator. (My old "Small Fry" wanders under +- 2 x 10-11.) It's a "nearly" analog circuit using three logic chips to perform simple tasks and a third-order phase-locked loop realized with two op-amps. The PLL behaves as though the lock frequency is 1 MHz due to the sampling technique (albeit updated only once per second) so the phase sensitivity is about 1 million times higher than if the phase comparison were done at 1 Hz. Read more click here

Arduino Uno Board - DC Motor Starter Circuit

Motor starter reduces the load, torque and current surge of a motor during startup. On starting, the motor takes more than five times the normal running current. This overheats the motor’s armature winding and creates a sudden voltage dip in the power supply, which can be avoided by using a motor starter. There are many types of motor starters. Here we describe an electronic DC motor starter using Arduino Uno board. This circuit controls both soft-start and soft-stop timings through pulse-width modulation (PWM).

Circuit and working

Circuit diagram of the DC motor soft-starter is shown in Fig. 1. In addition to Arduino Uno board (Board1), it uses PIC817 optocoupler (IC1), p-channel IRF9530 MOSFET (T1), 1N4007 rectifier diode (D1), 12V DC motor (M1) for testing, bi-colour LED (LED1) and a few other components.

Arduino Uno Board - DC Motor Starter
Fig. 1: Circuit diagram of DC motor starter using Arduino Uno

Arduino Uno board is an important part of the circuit that generates PWM signals. Pushbuttons (S1 and S2) are used to soft-start and soft-stop the motor. The bi-colour LED indicates whether the motor is in soft-start or soft-stop mode.

When the circuit is switched on, the motor is at rest and LED1 off. When push button S1 is pressed momentarily, the voltage across the motor increases gradually and attains maximum voltage after the predetermined soft-start timing. So the motor first starts at a slow speed. In this state, LED1 emits green light. After the soft-start time, i.e., in running condition, LED1 emits orange light, indicating that the motor is running at the rated speed.

If pushbutton S2 is pressed momentarily while the motor is running at the rated speed, the voltage across the motor decreases gradually and becomes zero after the soft-stop time. So the motor speed also decreases gradually and it finally stops after the soft-stop time. In this state, LED1 emits red colour. After the soft-stop time, LED1 doesn’t glow, indicating that the motor is at rest.

Arduino Uno is programmed such that if switch S1 or S2 is pressed more than once before the timing ends, it executes only once. This prevents the motor from restarting suddenly.
The circuit is isolated by an optocoupler (IC1) so that any disturbance in the motor power supply doesn’t affect the Arduino Uno board. The freewheeling diode (D1) gives additional protection over induced voltage when the motor is turned off.

The circuit’s operation is controlled using the software program loaded into the internal memory of Arduino Uno board. The program (softs.ino) is written in Arduino programming language sketch. Arduino IDE is used to compile and upload the program to the Arduino board.

Construction and testing

A PCB layout of the DC motor soft-starter is shown in Fig. 2 and its components layout in Fig. 3. After assembling the circuit on a PCB, connect CON2 to Arduino Uno board through external male-to-male jumper wires. After uploading the code to Board1, enclose the assembled PCB along with Board1 in a suitable plastic box.

The circuit works off the 5V USB power supply used for Arduino Uno board. Regulated 12V power supply is used to operate the DC motor.

Fig. 2: PCB layout of the DC motor starter using Arduino Uno

Fig. 3: Components layout for the PCB

The circuit can be converted into an AC motor soft-starter by using thyristors in place of MOSFET T1. It can be used along with device control projects. Additional protection and closed-loop control can be included, if required. Different timings and PWM values can be set for both soft-start and soft-stop.

Sourced By: Streampowers

APEX - 500W Power Amplifier B500 Circuit Diagram

This the easy and simple APEX - 500W Power Amplifier B500 Circuit Diagram. Power amplifier circuit schematic APEX following B500 visible part of the Pre-Amp use type IC NE5532. The output of IC NE5532 is given to the driver amplifier transistor. Part of these drivers will have two different outputs of phase from each other by 180 °. Part driver consists of transistors Q1, Q2, Q3 and Q4. Because the final amplifier circuit requires considerable input signal, then the driver is compiled with Darlington configuration.

APEX  - 500W Power Amplifier B500 Circuit Diagram
APEX  - 500W Power Amplifier B500 Circuit Diagram

Kits B500 APEX 500W Power Amplifier

To be able to work optimally, the power amplifier circuit B500 APEX requires ration symmetrical voltage of ± 90 volts, with a current 15-20 Ampere. Use the original transistor amplifier, especially on the final / final, because the source of the applied voltage (± 90 volts) just for the ideal transistor or original. If unsure transistor used is not genuine, then do not ever use a working voltage of ± 90 Volts, because it can lead to the final amplifier transistor broken / damaged. To test this, use a voltage gradually, ranging from ± 25V, ± 30V, ± 45V, and so on.

In the assembly do not forget to give the room a good cooling in all transistor power, attach the fan (blower) to be stable when working at maximum volume primarily for purposes such as concerts stage.

Sourced By: elcircuit

Introduction to Amplifier (Rise)

Amplification is the method of increasing the amplitude of a AC signal current or voltage such as audio signal for sound or video signal for a television picture. The amplifier allows a small input signal to control a bigger amount of power in the output circuit. The output signal is a replica of the original input signal but has higher amplitude.

Amplification is necessary as in most applications, the signal is weak to be used directly. For example, an audio output of 1mV from a microphone is unable to drive a loud speaker which requires a few volts to operate. Hence, the signal require to be amplified to a few volts before it can be fed in to the loud speaker.

NP N Transistor Circuit Configurations
An example of different type of transistor configurations in the circuit.

(1) The common emitter(CE) circuit makes use of emitter as its common electrode. The input signal is applied to the base and the amplified output is taken from the collector. This is the usually use because it's the best combination of current gain & voltage gain.

(2) The common base (CB) circuit makes use of base as its common electrode. The input signal is applied to the emitter & the amplified output is taken from the collector. The comparatively high emitter current compared to the base current ends in low input impedance value. For this reason, the CB circuit is never used.

(3) The common collector (CC) circuit makes use of collector as its common electrode. The input signal is applied to the base & the amplified output is taken from the emitter. This circuit is also called an emitter follower. This name means that the output signal voltage at the emitter follows the input signal at the base with the same phase but less amplitude. The voltage gain is less than one & is usually used for impedance matching. It's high input at the base as a load for the earlier circuit & low output impedance at the emitter as a signal source for the next circuit.


They can be classified in to classes A, B, C & AB. They are defined based on the percent of the cycle of input signal that can produce output current.

In Class A, the output current flows for the full cycle of 360 degree of input signal. The distortion is the lowest with around 5% to 10% &an efficiency of 20% to 40%. In general, most tiny signal operate class A

In Class C, the output current flows for less than half of the input cycle. Typical operation is 120 degree of input current in the coursework of the positive half cycle of the input current. This class has an efficiency of 80% but has the highest distortion. This class is usually used for RF amplification with a tuned circuit in the output.

In Class B, the output current flows for half of the input cycle which is around 180 degree. Class B operation lies between class A & class C. Classes B are usually connected in pairs & in such a circuit called push-pull amplifier. The push pull is often used for audio power output to a loud speaker.

In Class AB, it offers a compromise between the low distortion of class A & the higher power of class B. It is usually used for push pull audio power amplifiers.

Telephone Call Recorder

Today phone has become an integral part of our lives. It is the most widely used communication tool in the world. Owing to its immense popularity & widespread use, there arises a necessity for call recording devices, which find application in call cent-res, stock broking firms, police, offices, homes, etc. Here they are describing a call recorder that makes use of only a few parts. But in order to understand its working, must first have the basic knowledge of standard phone wiring as well as a stereo plug.

In India, land-line rings primarily use RJ11 wiring, which has wireless-tip & ring. While tip is the positive wire, ring is the negative. & together they complete the phone circuit. In a phone line, voltage between tip & ring is around 48V DC when handset is on the cradle(idle line). In order to ring the phone for an incoming call, a 20Hz AC current of around 90V is superimposed over the DC voltage already present in the idle line. The negative wire from the phone line goes to IN1, while the positive wire goes to IN2. Further, the negative wire from OUT1 & the positive wire from OUT2 are connected to the phone. All the resistors used are 0.25W carbon film resistors & all the capacitors used are rated for 250V .

The negative terminal of To AUX IN is connected to pin one of the stereo jack while the positive terminal is connected to pins two and three of the stereo jack. This stereo jack, in turn, is connected to the AUX IN of any recording tool, such as computer, audio cas-setts player, CD player, DVD player, etc. Here they shall be connecting it to a computer. When a call comes in, around 90V AC current at 20Hz is superimposed over the DC voltage already present in the idle line.

This current is converted in to DC by the diodes & fed to resistor R1, which reduces its magnitude & feeds it to LED1. The current is further reduced in magnitude by the resistor R2 & fed to the right & left channels of the stereo jack, which are connected to the AUX IN port of a computer. Audio recording application,can be used to record the call. When a call comes in, needs to launch the audio recording program and start recording.

For phone recording, basically connect the stereo jack to the AUX IN port of the PC. Install the Audacity audio recorder . Run the executable Audacity file. By & sizable window, you will discover a drop-down box in the top right corner. From this box, select the AUX option. Now you are prepared to record any call. As soon as a call comes in, press the record button present in the Audacity main window & then pick up the phone receiver & answer the call. Press the cease button one time the call ends. Now go to the file menu & select the Export as WAVE option & save the file in a desired location.

You may change the worth of resistor R2 in case you require to change the output volume. You can use a variable resistor in series with R2 to vary the volume of the output. The recorded audio clip can be edited using different options in the Audacity application. You can assemble the circuit on a general-purpose PCB & enclose it in a small cabinet. Use an RJ11 connector & stereo jack for connecting the phone set & computer (for call recording). Phone cords can be used to connect to the phone line & the circuit. Use of a shielded cable is recommended to reduce disturbances in the recording. These may even be reduced by increasing the worth of R2 to about 15 kilo-ohms.

4-Digit Alarm Control Keypad

Schematic Diagram


The Keypad must be the kind with common terminal  & a separate connection for each key. On a 12 key pad  look for 13 terminals. The matrix type with 7 or 8 terminals will not do. On the Support Page you will find details of how to Make Your Own Keypad.

The relay is energized by pressing a single key. Select the key you need to make use of and connect it to terminal E. Select the keys you need to make use of for your security code and connect them to A B C & D. Wire the common lead to R1- and all the remaining keys to F.

When you press E the relay energizes & the 12-volt output moves from the off to the set terminal. The green LED also lights. It provides  visual indication that the alarm is set.

When you press keys "A B C and D" in the right order - the relay de-energizes - & the 12-volt output returns to the "off" terminal. The green LED is also extinguished - to indicate that the alarm is switched off.

The remaining keys - those not wired to "A B C D and E" - are connected to "F". Whenever of these "Wrong" keys is pressed - the tried code entry fails - and the code entry sequence is reset.

With a 12-key pad - over ten 000 different codes are available. In the event you need a more secure code - you could basically use a bigger keypad with more "Wrong" keys wired to "F". A 16-key pad gives over 40 000 different codes. In the event you make a mistake while entering the code - basically start again.

The Support Material for this circuit includes a step-by-step guide to the construction of the circuit board - a parts list - a detailed circuit description - and more.

The same thing happens if "C" or "D" is pressed out of sequence. If "C" is pressed before "B" - or "D" is pressed before "C" - the tried code entry will fail. And the code entry sequence will reset.

Veroboard Layout








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10 W Audio Amplifier Circuit Diagram

This design is based on the 18 Watt Audio Amplifier, and was developed mainly to satisfy the requests of correspondents unable to locate the TLE2141C chip. It uses the widespread NE5532 Dual IC but, obviously, its power output will be comprised in the 9.5 - 11.5W range, as the supply rails cannot exceed ±18V.

10 W Audio Amplifier Circuit Diagram

10 W Audio Amplifier Circuit Diagram

As amplifiers of this kind are frequently used to drive small loudspeaker cabinets, the bass frequency range is rather sacrificed. Therefore a bass-boost control was inserted in the feedback loop of the amplifier, in order to overcome this problem without quality losses. The bass lift curve can reach a maximum of +16.4dB @ 50Hz. In any case, even when the bass control is rotated fully counterclockwise, the amplifier frequency response shows a gentle raising curve: +0.8dB @ 400Hz, +4.7dB @ 100Hz and +6dB @ 50Hz (referred to 1KHz).


    Can be directly connected to CD players, tuners and tape recorders.
    Schematic shows left channel only, but C3, C4, IC1 and the power supply are common to both channels.
    Numbers in parentheses show IC1 right channel pin connections.
    A log type for P2 will ensure a more linear regulation of bass-boost.
    Do not exceed 18 + 18V supply.
    Q3 and Q4 must be mounted on heatsink.
    D1 must be in thermal contact with Q1.
    Quiescent current (best measured with an Avo-meter in series with Q3 Emitter) is not critical.
    Set the volume control to the minimum and R3 to its minimum resistance.
    Power-on the circuit and adjust R3 to read a current drawing of about 20 to 25mA.
    Wait about 15 minutes, watch if the current is varying and readjust if necessary.
    A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of J1, P1, C2, C3 &C4. Connect C9 to the output ground.
    Then connect separately the input and output grounds to the power supply ground.


P1_________________22K   Log.Potentiometer (Dual-gang for stereo)
P2________________100K   Log.Potentiometer (Dual-gang for stereo)
R1________________820R   1/4W Resistor
R2,R4,R8____________4K7  1/4W Resistors
R3________________500R   1/2W Trimmer Cermet
R5_________________82K   1/4W Resistor
R6,R7______________47K   1/4W Resistors
R9_________________10R   1/2W Resistor
R10__________________R22   4W Resistor (wirewound)

C1,C8_____________470nF   63V Polyester Capacitor
C2,C5_____________100µF   25V Electrolytic Capacitors
C3,C4_____________470µF   25V Electrolytic Capacitors
C6_________________47pF   63V Ceramic or Polystyrene Capacitor
C7_________________10nF   63V Polyester Capacitor
C9________________100nF   63V Polyester Capacitor

D1______________1N4148    75V 150mA Diode

IC1_____________NE5532    Low noise Dual Op-amp

Q1_______________BC547B   45V 100mA NPN Transistor
Q2_______________BC557B   45V 100mA PNP Transistor
Q3_______________TIP42A   60V 6A    PNP Transistor
Q4_______________TIP41A   60V 6A    NPN Transistor

J1__________________RCA audio input socket

Power supply parts:

R11_________________1K5  1/4W Resistor

C10,C11__________4700µF   25V Electrolytic Capacitors

D2________________100V 4A Diode bridge
D3________________5mm. Red LED

T1________________220V Primary, 12 + 12V Secondary 24-30VA Mains transformer

PL1_______________Male Mains plug

SW1_______________SPST Mains switch

Technical data:

Output power:
    10 Watt RMS into 8 Ohm (1KHz sinewave)
    115 to 180mV input for 10W output (depending on P2 control position)
Frequency response:
    See Comments above
Total harmonic distortion @ 1KHz:
    0.1W 0.009% 1W 0.004% 10W 0.005%
Total harmonic distortion @ 100Hz:
    0.1W 0.009% 1W 0.007% 10W 0.012%
Total harmonic distortion @ 10KHz:
    0.1W 0.056% 1W 0.01% 10W 0.018%
Total harmonic distortion @ 100Hz and full boost:
    1W 0.015% 10W 0.03%
Max. bass-boost referred to 1KHz:
    400Hz = +5dB; 200Hz = +7.3dB; 100Hz = +12dB; 50Hz = +16.4dB; 30Hz = +13.3dB
Unconditionally stable on capacitive loads

18W Car Stereo Amplifier Circuit Diagram

This automobile stereo amplifier project is a class AB audio power amplifier using the Hitachi HA13118 module. It not only can be used in automobile application but also in any transportable or home amplifier process. It is simple to construct & has a maximum of outside parts. The module has a high power output from a low voltage supply using the bridge tied load system, & a high gain of 55dB.

This project will be useful in applications where the input signal is a low level, without requiring the use of a separate pre-amplifier. This IC module has a built in surge protection circuit, thermal shutdown circuit, ground fault protection circuit & power supply fault protection circuit making it reliable.
The Specifications of this project 
D.C. Input : 8 – 18V at 1-2 A

Power output : 18W maximum, 4 ohm load, 18V DC supply

S/N ratio : > 70 dB

THD : < 0.2% @ 1W

Freq. Response : ~ 30 Hz to 30 kHz, –3 dB

Input level : < 25 mV, for full output (G > 50dB)

Input Impedance : ~ 30 k ohm

The supply voltage necessary for this project is 8 -18V DC, at least one to two Amps. Maximum output power will only be obtained with a power supply of 18V at greater than two A, using a four ohm speaker. The power supply ought to be well filtered to reduce mains hum, a regulated supply will reduce noise even further. Additional filtering is unnecessary if operating from a battery supply.

Circuit Diagram Description

Most of the circuitry is contained within the amplifier module. C10 is the input coupling capacitor and blocks DC from the input. C11 bypasses any RF which may be present at the input. C1 & C2 provide an AC ground for the inverting inputs of the IC. R1/C7 and R2/C8 provide a high frequency load for stability with difficult speakers. C five & C six provide bootstrap feedback for the IC. C9 & C12 provide power supply filtering.

18W Car Stereo Amplifier Circuit Diagram

18W Car Stereo Amplifier Circuit Diagram

An externally mounted logarithmic potentiometer of between 10k ohm and 50k ohm, is used depending on the desired input impedance. The impedance ought to be keep as high as feasible for a guitar amp, unless using a separate pre-amp. Make sure-that the heat sink is mounted to the module.

1 W Home Stereo Amplifier Circuit Diagram

This is a one watt home stereo amplifier module project using the KA2209 IC from Samsung, which is equivalent to the TDA2822. It operates from 3-12V DC & will work from a battery since the dormant current drain is low. It requires no heat sink for normal use. The input & output are both ground referenced. Maximum output will be obtained with a 12V power supply & 8 ohm speaker, however it is suitable for driving headphones from a supply as low as 3V.

The Specifications of the home stereo amplifier :

D.C. input : 3 – 12 V at 200 – 500 mA max
Idle current : approx. 10 mA
Power output : > 1 Watt max. 4-8 ohms, 12V DC
Freq. Resp. : approx. 40 Hz to 200 kHz, 8 ohm, G=10
THD : < 1 % @ 750 mW, 4-8 ohm, 12V
Gain : approx. x10 (20 dB) OR x100 (40dB)
S/N ratio : > 80 dB, G = 20 dB
Sensitivity : < 300 mV, G = 20 dB
Input Impedance : approx. 10 k ohm


The gain is adjustable from ten to 100, i.e. twenty to 40 dB. Start with feedback resistors R1 and R3 of 1k ohm, this will give a gain of ten which ought to be adequate for most applications. In case you need more gain, you can remove resistors R1 and R3.This will give a gain of about 100, or 40 dB.The input attenuation can be adjusted by the potentiometer which can be used as a volume control. The IC gain ought to be kept as low as necessary to accomplish full output, with the in put potentiometer and your signal source at maximum.

1 W Home Stereo Amplifier Circuit Diagram

1 W Home Stereo Amplifier Circuit Diagram

Voltage Gain = 1+ R1/R2 = 1+R3/R4, however the maximum gain with no outside feedback is about 100, or 40dB. (GdB = 20log Gv)

This will keep the signal to noise ratio as high as feasible. Additional gain provided by the amplifier will reduce the S/N ratio by a similar amount, since the input noise figure is constant. Other values for R1 and R3 of between 1k and 10k ohm can be used if an intermediate gain level is necessary.

If driving a pair of headphones, you may also need a 100 ohm resistor in series with each output to reduce the output level, depending on headphone impedance & sensitivity. Make positive you start with the volume right down to check. Numerous headphones may be driven from the amplifier in the event you wish, since most headphones have at least 16 ohm impedance, or more often 32 ohm.

There are only a few outside parts, the IC contains most of the necessary circuitry. R1,R2 and R3,R4 are the feedback resistors. C1 provides power supply decoupling. C2 and C3 are the input coupling capacitors, which block any DC that might-be present on the inputs. C4,C5 block DC in the feed back circuit from the inverting inputs, and C6,C7 are the output coupling capacitors. C8, R5 and C9,R6 act as Nobel networks providing a high frequency load to maintain stability at frequencies where loud speaker inductive reactant may become excessive. The pot provides adjustable input level attenuation.

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