Discrete Virtual Ground Circuit Diagram

Here is the simple virtual ground circuit based on discrete components. This simple design comes from miniaturization guru Sijosae. Is to make a buffer from generic discrete components. The transistors can be most any complementary pair of small-signal transistors. Suitable alternatives are the PN2222A and PN2907A. The diodes are generic small-signal types. An acceptable alternative is the 1N914. This circuit has better performance than a simple resistive divider virtual ground, and the parts cost is lower than for any other circuit mentioned here. It is, however, the least accurate of the buffered virtual ground circuits.

Discrete Virtual Ground Circuit Diagram

 

 Parts:

R1,R2 = 4.7K
R3,R4 = 4.7R
C1,C2 = 470uF-25V
C3,C4 = 47uF-25V
D1,D2 = 1N4148
Q1 = 2SC1384
Q2 = 2SA684
B1 = Battery

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5 Watt Class-A Audio Amplifier Circuit diagram

This solid-state push-pull single-ended Class A circuit is capable of providing a sound comparable to those valve amplifiers, delivering more output power (6.9W measured across a 8 Ohm loudspeaker cabinet load), less THD, higher input sensitivity and better linearity. Voltage and current required for this circuit are 24V and 700mA respectively, compared to 250V HT rail and 1A @ 6.3V filament heating for valve-operated amplifiers. The only penalty for the transistor operated circuit is the necessity of using a rather large Heatsink for Q2 and Q3 (compared to the maximum power delivered).In any case, the amount of heat generated by this circuit can be comparable to that of a one-valve amplifier. An optional bass-boost facility can be added, by means of R5 and C5.

5 Watt Class-A Audio Amplifier Circuit diagram

Parts:

P1 = 47K
R1 = 100K
R2 = 12K
R3 = 47K
R4 = 8.2K
R5 = 1.5K
R6 = 2.7K
R7 = 100R
R8 = 100R
R9 = 560R-1/2W
R10 = 1R-1/2W
Q1 = BC560
Q2 = BD439
Q3 = BD439
C1 = 10uF-63V
C2 = 10uF-63V
C3 = 47uF-25V
C4 = 100uF-35V
C5 = 150nF-63V
C6 = 220uF-25V
C7 = 220uF-25V
C8 = 1000uF-25V
SPKR = 5W-8R Speaker

Notes:

• If necessary, R2 can be adjusted to obtain 13V across C8 positive lead and negative ground.
• Total current drawing of the circuit, best measured by inserting the probes of an Avo-meter across the positive output of the power supply and the positive rail input of the amplifier, must be 700mA. Adjust R8 to obtain this value if necessary.
• Q2 and Q3 must be mounted on a finned Heatsink of 120x50x25mm. Minimum dimensions.
• Add R5 and C5 if the bass-boost facility is required.

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Digital Volume Control Circuit Diagram

This circuit could be used for replacing your manual volume control in a stereo amplifier. In this circuit, push-to-on switch SW1 controls the forward (volume increase) operation of both channels while a similar switch SW2 controls reverse (volume decrease) operation of both channels. A readily available IC from Dallas semiconductor, DS1669 is used here.

Digital Volume Control Circuit Diagram

Digital Volume Control Circuit Diagram

Parts:

J1 = RCA Audio Input Socket
J2 = RCA Audio Input Socket
C1 = 0.1uF-16V Ceramic Disc Capacitor
C2 = 0.1uF-16V Ceramic Disc Capacitor
C3 = 0.1uF-16V Ceramic Disc Capacitor
IC1 = DS1669 (is available from Dallas SCo.
SW1 = Momentary Push Button Switch
SW1 = Momentary Push Button Switch

Notes:

• Replaces mechanical variable resistors.
• Electronic interface provided for digital as well as manual control.
• Wide differential input voltage range between 4.5 and 8 volts.
• Wiper position is maintained in the absence of power.
• Low-cost alternative to mechanical controls.
• Applications include volume, tone, contrast, brightness, and dimmer control.
• The circuit is extremely simple and compact requiring very few external components.
• The power supply can vary from 4.5V to 8V.
• The input signal should not fall below -0.2 volts.

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Simple Circuit Board Checker

This little circuit indicates the basic integrity of a printed board, detecting 0V, positive supply voltage from less than 3V to 30V and floating parts. If the probe is floating, as it would be in a broken track, then both LEDs barely light up, since there is no current to drive the transistors, but if the probe touches 0V or a positive voltage one or other lights. A digital signal should light them in proportion to the mark-space ratio whereas the output of a circuit oscillating at a frequency rate below about 20Hz will cause the LEDs to flicker alternatively. The LEDs will illuminate always at a constant intensity, no matter the voltage supply used, because they are fed by a very simple FET constant-current generator (Q1).

Simple Circuit Board Checker  Circuit diagram

Circuit Board Checker Circuit Diagram

Parts:

R1 = 22K
R2 = 22K
D1 = Red LED
D2 = Green LED
Q1 = BF245
Q2 = BC547
Q3 = BC557

Notes:

• The Black clip must be connected to the negative ground of the board under test.
• The Red clip should be connected to a positive voltage source (not exceeding 30V) available on the same board.
• Metal probe is suitable for this circuit.
• Two Miniature Crocodile Clips (Red and Black) are also necessary.

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Stabilized Regulated Power Supply Circuit Diagram

This circuit of power supply, is very simple and easy to built, it can be assembled on a general-purpose PCB, finding its materials is very easy and cost-small. The output voltage is stabilized and is regulated in the region from 0V until + 15V dc, with biggest provided current 1 A. The regulation becomes with the P1. The Q1 is classic power transistor and it needs to be placed on a cool rib (Heatsink), when it works continuously in the region of biggest current it gets hot. The type of transformer is standard in the market.

Stabilized Regulated Power Supply Circuit Diagram

Stabilized Power Supply Circuit Diagram

Parts:

P1 = 330R-Potentiometer
R1 = 560R-2W
C1 = 2200uF-35V
C2 = 100uF-35V
C3 = 10uF-25V
C4 = 220uF-25V
C5 = 100nF-63V
D1 = 18V-1.5W Zener
Q1 = 2N3055 NPN Transistor
T1 = 220VAC – 18V@ 1.5A
BR1 = 4x1N4007 Diode Bridge
SW1 = Mains On-Off Switch

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Simple Mobile Phone Battery Charger

Mobile phone chargers available in the market are quite expensive. The circuit presented here comes as a low-cost alternative to charge mobile telephones/battery packs with a rating of 7.2 volts, such as Nokia 6110/6150.

 Circuit diagram:

Mobile Phone Battery Charger Circuit Diagram

 Parts

R1 = 1K
R2 = 47R
R3 = 10R
R4 = 47R
C1 = 1000uF-25V
D1 = LEDs any color
D2 = LEDs any color
D3 = LEDs any color
D4 = 1N4007
D5 = 1N4007
IC1 = LM7806
T1 = 9VAC Xformer 250mA
BR1 = Diode bridge 1A

Circuit Operation:

The 220-240V AC mains supply is down-converted to 9V AC by transformer T1. The transformer output is rectified by BR1 and the positive DC supply is directly connected to the charger’s output contact, while the negative terminal is connected through current limiting resistor R2. D2 works as a power indicator with R1 serving as the current limiter and D3 indicates the charging status. During the charging period, about 3 volts drop occurs across R2, which turns on D3 through R3.

An external DC supply source (for instance, from a vehicle battery) can also be used to energies the charger, where R4, after polarity protection diode D5, limits the input current to a safe value. The 3-terminal positive voltage regulator LM7806 (IC1) provides a constant voltage output of 7.8V DC since D1 connected between the common terminal (pin 2) and ground rail of IC1 raises the output voltage to 7.8V DC. D1 also serves as a power indicator for the external DC supply. After constructing the circuit on a veroboard, enclose it in a suitable cabinet. A small heat sink is recommended for IC1.

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Analog to Digital Converter (ADC) Circuits Diagram

Normally analogue-to-digital converter (ADC) needs interfacing through a microprocessor to convert analogue data into digital format. This requires hardware and necessary software, resulting in increased complexity and hence the total cost. The circuit of A-to-D converter shown here is configured around ADC 0808, avoiding the use of a microprocessor.

The ADC 0808 is an 8-bit A-to-D converter, having data lines D0-D7. It works on the principle of successive approximation. It has a total of eight analogue input channels, out of which any one can be selected using address lines A, B and C. Here, in this case, input channel IN0 is selected by grounding A, B and C address lines. Usually the control signals EOC (end of conversion), SC (start conversion), ALE (address latch enable) and OE (output enable) are interfaced by means of a microprocessor. However, the circuit shown here is built to operate in its continuous mode without using any microprocessor.

Therefore the input control signals ALE and OE, being active-high, are tied to Vcc (+5 volts). The input control signal SC, being active-low, initiates start of conversion at falling edge of the pulse, whereas the output signal EOC becomes high after completion of digitization. This EOC output is coupled to SC input, where falling edge of EOC output acts as SC input to direct the ADC to start the conversion. 

Analog to Digital Converter (ADC) Circuit Diagram

As the conversion starts, EOC signal goes high. At next clock pulse EOC output again goes low, and hence SC is enabled to start the next conversion. Thus, it provides continuous 8-bit digital output corresponding to instantaneous value of analogue input. The maximum level of analogue input voltage should be appropriately scaled down below positive reference (+5V) level. 

The ADC 0808 IC requires clock signal of typically 550 kHz, which can be easily derived from an astable multivibrator constructed using 7404 inverter gates. In order to visualize the digital output, the row of eight LEDs (LED1 through LED8) have been used, wherein each LED is connected to respective data lines D0 through D7. Since ADC works in the continuous mode, it displays digital output as soon as analogue input is applied. The decimal equivalent digital output value D for a given analogue input voltage Vin can be calculated from the relationship.

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Simple Train Mounted Camera Battery Charger

Simple Train Mounted Camera Battery Charger circuit will keep the battery for a train mounted camera charged and will shut the camera off after a few seconds when power is no longer applied to the track. The circuit is designed for DCC systems and the battery is essentially used as a capacitor as it is not allowed to become discharged. The battery also controls the voltage to the camera as any current passed through R1 that is not needed by the camera is shunted through the battery. This is an inefficient but cheap way to control the voltage. 

Train Mounted Camera Battery Charger Circuit Diagram

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Wire-Break Alarm With Delay Circuits Diagram

Simple Wire-Break Alarm With Delay  Alarm and Security Here is a simple circuit of wire-break alarm that activates after a delay of 15 to 30 seconds. When the thin-wire loop running across the entrance door is broken, the alarm sounds after a delay of 15 to 30 seconds, the time period set through VR1. Thus the occupants get sufficient time to lock the room from the outside and catch the thief. 

 The circuit uses CD4060, which is a 14-stage ripple-carry binary counter/divider and oscillator. It is wired as a timer here and does not need input pulse for trigger. CD4060 gets activated as soon as the power supply is switched on. Output O13 of CD4060 goes high after the lapse of preset delay set through VR1. Transistor SL100 (T2) is wired as a switch to power the timer section built around CD4060. When the wire loop is closed, transistor T2 does not conduct. So power to the timer circuit is not available and the piezo buzzer does not sound. 

Wire-Break Alarm With Delay Circuit Schematic

On the other hand, when the wire loop is broken by some intruder, transistor T2 conducts to power the circuit and the piezobuzzer sounds after 15 to 30 seconds. IC1 can be reset by connecting the wire loop or interrupting the supply. The circuit works off regulated 9V-12V. Assemble it on a general-purpose PCB and enclose in a metallic or plastic box of appropriate size. Connect piezobuzzer PZ1 through external wires and complete the installation.

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A Simple Hearing Aid

Commercially available hearing aids are quite costly. Here is an inexpensive hearing aid circuit that uses just four transistors and a few passive components.

Hearing Aid Circuit Diagram

Parts:

R1 = 2.2K
R2 = 680K
R3 = 3.3k
R4 = 220K
R5 = 1.5K
R6 = 220R
R7 = 100K
R8 = 680K
C1 = 104pF
C2 = 104pF
C3 = 1uF/10V
C4 = 100uF/10V
C5 = 100uF/10V
Q1 = BC549
Q2 = BC548
Q3 = BC548
Q4 = BC558
J1 = Headphone jack
B1 = 2x1.5V Cells
SW1 = On/Off-Switch

Circuit Operation:

On moving power switch SW1 to ‘on’ position, the condenser microphone detects the sound signal, which is amplified by Q1 and Q2. Now the amplified signal passes through coupling capacitor C3 to the base of Q3.
The signal is further amplified by Q4 to drive a low impedance earphone. Capacitors C4 and C5 are the power supply decoupling capacitors. The circuit can be easily assembled on a small, general-purpose PCB or a Vero board.

It operates off a 3V DC supply. For this, you may use two small 1.5V cells. Keep switch S to ‘off’ state when the circuit is not in use. To increase the sensitivity of the condenser microphone, house it inside a small tube.

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Infra-red Remote Control Tester

As I was developing my IR Extender Circuit, I needed to find a way of measuring the relative intensities of different Infra red light sources. This circuit is the result of my research. I have used a photodiode, SFH2030 as an infra red sensor. A MOSFET opamp, CA3140 is used in the differential mode to amplify the pulses of current from the photodiode. LED1 is an ordinary coloured led which will light when IR radiation is being received.

The output of the opamp, pin 6 may be connected to a multimeter set to read DC volts. Infra red remote control strengths can be compared by the meter reading, the higher the reading, the stronger the infra red light. I aimed different remote control at the sensor from about 1 meter away when comparing results. For every microamp of current through the photodiode, about 1 volt is produced at the output. A 741 or LF351 will not work in this circuit. Although I have used a 12 volt power supply, a 9 volt battery will also work here.

Circuit diagram:

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Simple Sensitive Optical Burglar Alarm Circuit Diagram

How to build a Simple Sensitive Optical Burglar Alarm Circuit Diagram ? This optical burglar alarm uses two 555 timer ICs. Both the ICs are wired as astable multivibrators. The first astable multivibrator built around IC1 produces low frequencies, while the second astable multivibrator built around IC2 produces audio frequencies.

Simple Sensitive Optical Burglar Alarm Circuit Diagram

General-purpose Darlington photo-transistor 2N5777 (T1) is used as the light sensor. To increase the sensitivity of the circuit, npn transistor BC547 (T2) is used.

Place phototransistor T1 where light falls on it continuously. Phototransistor T1 receives light to provide base voltage to transistor T2 . As a result, transistor T2 conducts to keep reset pin 4 of IC1 at low level. This disables the first multivibrator (IC1) and hence the second multivibrator (IC2) also remains reset so the alarm (loudspeaker LS1) does not sound.

When light falling on Darlington phototransistor T1 is obstructed, transistor T2 stops conducting and reset pin 4 of IC1 goes high. This enables the first multivibrator (IC1) and hence also the second multivibrator (IC2). As a result, a beep tone is heard from speaker LS1. The beep rate can be varied by using preset VR1, while the output frequency of IC2 can be varied by using another preset VR2.

The circuit works off a simple 6V-12V DC power supply.

Sourced By: EFY Author:  Pradeep G.

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Lights Control for Model Cars Circuit Diagram

The author gave his partner a radio controlled (RC) model car as a gif t. She found it a lot of fun, but thought that adding realistic lights would be a definite improvement. So the author went back to his shed, plugged in his soldering iron, and set to work equipping the car with realistic indicators, headlights, tail lights and brake lights.

Lights Control for Model Cars Circuit Diagram

The basic idea was to tap into the signal from the radio control receiver and, with a bit of help from a microcontroller, simulate indicators using flashing yellow LEDs and brake lights using red LEDs. Further red LEDs are used for the tail lights, and white LEDs for the headlights. Connectors JP4 and JP5 (channel 0) are wired in parallel, as are JP6 and JP7 (channel 1), allowing the circuit to be inserted into the servo control cables for the steering and drive motor respectively. The ATtiny45 micro-controller takes power from the radio receiver via diode D1. T1 and T2 buffer the servo signals to protect IC1’s inputs from damage. 

IC1 analyses the PWM servo signals and gen-erates suitable outputs to switch the LEDs via the driver transistors. T3 drives the two left indicators (yellow), T4 the two right indica-tors, and T5 the brake LEDs (red). The red tail lights (JP2-8 and JP2-8) and the white head-lights (JP2-9 and JP2-10) are lit continuously. The brake lights are driven with a full 20 mA, so that they are noticeably brighter than the tail lights, which only receive 5 mA. If you wish to combine the functions of tail light and brake light, saving t wo red LEDs, sim-ply connect pin 10 of JP2 to pin 14 and pin 12 to pin 16. Then connect the two combined brake/tail LEDs either at JP2-5 and JP2-6 or at JP2-7 and JP2-8.

JP3 is provided to allow the use of a separate lighting supply. This can either be connected to an additional four-cell battery pack or to the main supply for the drive motor. The val-ues given for resistors R8 to R17 are suitable for use with a 4.8 V supply. JP2 can take the form of a 2x10 header.

As usual the sof t ware is available as a free download from the Elektor web pages accom-panying this article[1], and ready-programmed microcontrollers are also available. The microcontroller must be taught what servo signals correspond to left and right turns, and to full throttle and full braking. First connect the fin-ished circuit to the radio control electronics in the car, making sure everything is switched of f. Fit jumper JP1 to enable configuration mode, switch on the radio control transmit-ter, set all proportional controls to their cen-tre positions, and then switch on the receiver. The indicator LEDs should first flash on both sides. Then the car will indicate left for 3 s: during this time quickly turn the steering on the radio control transmitter fully to the left and the throt tle to full reverse (maximum braking).

Hold the controls in this position until the car starts to indicate right. Then set the controls to their opposite extremes and hold them there until both sides flash again. Now, if the car has an internal combustion engine (and so cannot go in reverse), keep the throttle control on full; if the car has an electric motor, set the throttle to full reverse. Hold this position while both sides are flashing. Configuration is now complete and JP1 can be removed. If you make a mistake during the configuration process, start again from the beginning.

Author: Manfred Stratmann - Copyright : Elektor

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1.5 - 35 Volt DC Regulated Power Supply

Here is the circuit diagram of regulated power supply. It is a small power supply that provides a regulated voltage, adjustable between 1.5 and 35 volts at 1 ampere. This circuit is ready to use, you just need to add a suitable transformer. This circuit is thermal overload protected because the current limiter and thermal overload protection are included in the IC.

Picture of the circuit:

1A Regulated Power Supply Circuit Schematic

Circuit diagram:

1A Regulated Power Supply Circuit Diagram

Transformer selection chart:

Transformer selection Guide-Table For Power Supply

Parts:
IC = LM317
P1 = 4.7K
R1 = 120R
C1 = 100nF - 63V
C2 = 1uF - 35V
C3 = 10uF - 35V
C4 = 2200uF - 35V
D1-D4 = 1N4007

Features:

• Just add a suitable transformer (see table)
• Great to power your projects and save money on batteries
• Suitable as an adjustable power supply for experiments
• Control DC motors, low voltage light bulbs, …

Specifications :

• Preset any voltage between 1.5 and 35V
• Very low ripple (80dB rejection)
• Short-circuit, thermal and overload protection
• Max input voltage : 28VAC or 40VDC
• Max dissipation : 15W (with heatsink)
• Dimensions : 52x52mm (2.1” x 2.1”)

Technical Specifications

• Input Voltage = 40Vdc max Transformer
• Output Voltage = 1.5V to 35Vdc
• Output Current = 1.5 Amps max.
• Power Dissipation = 15W max (cooled)

Note:

• It has not to be cooled if used for small powers. 28 Volt AC max is allowed for the input voltage.

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Canon EOS M Digital Camera Enters into the Mirrorless Territory

Canon has long been a leader in the world of DSLRs, but when it comes to smaller sized shooters, Canon had largely concentrated on commercially viable consumer and prosumer class digital cameras, not really treading on the mirrorless camera technology known as Micro Four Thirds which has been around for some years now. The mirrorless camera comes close to a DSLR in terms of image quality, and yet is far less bulkier in terms of size, not to mention allowing you to change a fair number of lenses (a market which is growing), making it a favorite secondary camera to many.

Well, Canon has finally decided to dip their toes into this particular market, by offering the Canon EOS M digital camera which is said to deliver exceptional EOS Full HD video quality with continuous autofocus, not to mention having it accompanied by a notable and expansive range of lenses.

Inspired by EOS technology, the EOS M will be able to leverage on the company’s core technologies, while distilling them down in order to deliver outstanding video capture capabilities without sacrificing image quality when it comes to still shots. Whenever you want to capture still images, the EOS M camera’s 18-megapixel APS-C-sized CMOS image sensor is more than capable of delivering a shallow depth of field, in addition to incredible low-light image quality and a wide dynamic range which is more than capable of capturing rich gradation and detail.

This is the latest member of the EOS family, where both videographers and photographers alike regardless of their level of professionalism and interest, will be able to play nice with a couple of lenses that were specially designed for Canon’s new camera format – namely the EF-M 22mm f/2 STM kit lens and the optional EF-M 18-55mm f/3.5-5.6 IS STM lens. Not only that, you are also able to make full use of your Canon EF and EF-S lenses courtesy of the optional Mount Adapter EF-EOS M.

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Mobile phone Circuits to Get Even smaller

Transceivers, appliances such as mobile phones that can send and receive messages, have become smaller and smaller over the last few years, but users are about to experience a new meaning in miniaturisation. 

Research at The Hong Kong University of Science & Technology (HKUST) has successfully combined a unique system architecture and new circuit design techniques to reduce them in size like never before. 

Principal Investigator Dr Howard Luong said the handset of a typical mobile phone today may contain between 150 and 300 separate electrical components.

His research group proposed and demonstrated circuit techniques that make it possible to combine many of these components to a single chip and therefore to significantly reduce the size of circuitry (see example in graphic). A US patent has been granted for one of the circuit techniques. 
 
The transformation applies to the CMOS (Complimentary Metal-Oxide Semiconductor) manufacturing process, which can produce integrated circuits and systems with the highest integration level at the lowest cost. Applying new techniques to the CMOS process, Dr Luong’s research enables many “off-chip” components to be combined to realize a system-on-chip. “But,” he said, “this integration created great challenges in circuit implementation.” Part of the research was to solve the problems by new circuit design techniques.
 
“The system architecture and circuitry go hand in hand, he added. “They must both work, or neither will be useful.”
The resulting design gives the highest component integration in the smallest chip area ever reported, said Dr Luong.
In his design, all off-chip components are fitted into a central chip measuring 36 mm with packaging, and 8mm without being packaged.
Dr Luong’s miniaturisation method means appliances will soon be made for even lower cost and lower power consumption in addition to being much smaller in size and lighter in weight.
“With the lowering of cost, size and power, many new and interesting applications will become possible and practical,” he said.
Low-power wireless transceivers, for example, could be integrated into implanted devices such as heart pacemakers to wirelessly transmit and receive information between patients and doctors or monitoring systems.
Wearable mobile phones as small as wrist watches at an affordable price could also become a reality.

Auther

Principal Investigator

Dr Howard Luong

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Smart Chocolate Block Schematic Diagram

What can be done, when two light bulbs in one light fitting are to be switched separately, but only one switch circuit is available? Simple: build a ‘smart chocolate block’ into the ceiling rose! The circuit is built from discrete components and with a bit of ingenuity can be fitted onto a printed circuit board measuring just a centimetre or two square.

When light switch S1 is operated for the first time lamp La1, which is connected in the usual way, lights; La2 remains dark. Electrolytic capacitor C1 starts to charge via rectifier diode D1 and resistors R1 and R2 until zener diode D3 conducts, limiting the voltage to about 6.8 V. This voltage is used as a supply for the rest of the circuit. The second lamp is connected via a triac and a fuse (1.5 A, medium speed recommended). The triac is triggered by T4, which can only happen when T3 does not pull its base down to ground. The first time the circuit is switched on this is the case, as we shall see below.
.

Smart Chocolate Block Schematic

Transistors T1 and T2 form a bistable flip-flop with a well-defined power-up state. R14 and R15 cause both transistors to be initially turned off. As the voltage across C1 rises, transistor T1, driven via resistors R7 and R9, turns on. The base drive for transistor T2, which is provided via D2, the low-pass filter formed by R6 and C2, and R5, would arrive a little later, but when T1 turns on it diverts the base current away from T2, which therefore remains turned off. This situation is stable: the base of T3 is not pulled down and so this transistor conducts.

To turn the second lamp on, switch S1 is opened and then, within a second or so, closed again. The effect of this action on the flip-flop is as follows.

When the switch is opened the voltage across C1 falls more rapidly than the volt-age across C2. The main reason for this is resistor R3, which is directly responsible for the discharge of C1; C2 can only discharge through the relatively high resistance of R5, since the other path is blocked by diode D2. This means that T2 is driven via R5 for one or two seconds longer than T1 is driven via R7 and R9. If during this time the supply voltage reappears, it can no longer drive the base of T1 via R7 as T2 is conducting all the current to ground. This situation is also stable, as C2 is recharged via D2 and R6.

When T2 conducts it pulls the base of T3 to ground, so that this latter transistor turns off. Darlington transistor T4 now conducts as its base is pulled high via R4. T4 now provides the trigger current for the triac via current limiting resistor R10, and the second lamp lights.

T5 and T6 together form a zero-crossing detector. It ensures that the triac is never triggered at a moment when the AC mains supply is at a high voltage point in its cycle. This avoids a rapid inrush current into La2, which would give rise to considerable radio interference. Also, trigger current is only required for the triac for a small fraction of the period of one cycle of the mains supply. If this current were drawn continuously from the low voltage supply, C1 would rap-idly discharge; R1 and R2 would have to be considerably reduced in resistance, which would increase the heat dissipation of the module, perhaps making it infeasible to build the circuit into a plastic ceiling rose.

Using the component values shown the triac is only driven when the instantaneous mains voltage is less than about 15 V in magnitude. The voltage divider formed by R11, R12 and R13 switches on the transistors T5 and T6 when the voltage is greater than +15V or less than –15 V respectively. The collectors of these transistors, which are connected together, pull the base of T4 down to ground or to a slightly negative voltage when the mains cycle is outside the desired phase window.

Any resistors across which mains voltages will be dropped are formed from two individual resistors wired in series to ensure that the maximum voltage specifications of ordinary 0.25 W components are not exceeded. This applies to R1 and R2, as well as R11 and R12. The whole circuit is at mains potentials and great care must be taken to observe all relevant safety precautions in construction and installation.

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Simple 50 to 300 MHz Colpitts Oscillator

Simple high efficiency Colpitts oscillator .In the higher frequency ranges, above 50 MHz, Colpitts oscillators are used because stray circuit capacitance will be in parallel with desired feedback capacitance and not cause undesirable spurious resonances that might occur with the tapped coil Hartley design.

Simple 50 to 300 MHz Colpitts Oscillator Circuit Diagram

The FM VCO shown is a grounded base design with feedback from collector to emitter. A Colpitts oscillator is one of a number of designs for electronic oscillator circuits using the combination of an inductance with a capacitor for frequency determination.As you can see in the circuit diagram , this electronic project require few electronic parts an provide a 50 MHz-300MHz VCO with a tuning range of 2:1 .

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Simple Energy-Saving Switch Schematic Diagram

Lights do not always need to be on at full power. Often it would be useful to be able to turn off the more powerful lights to achieve softer illumination, but this requires an installation with two separately-switch-able circuits, which is not always available.
. .

 Energy-Saving Switch Circuit Image


If the effort of chasing out channels and replastering for a complete new circuit is too much, then this circuit might help. Normal operation of the light switch gives gentle illumination (LA1). For more light, simply turn the switch off and then immediately (within 1 s) on again. The circuit returns to the gentle light set-ting when switched off for more than 3 s. There is no need to replace the light switch with a dual version: simply insert this circuit between switch and lamp.
.
Energy-Saving Switch Circuit Diagram


Parts List:
Resistors:
R1 = 100Ω
R2 = 680Ω
Capacitor:
C1 = 4700µF 25 V
Semiconductors:
D1,D2 = 1N4001
Miscellaneous:
K1,K2,K3 = 2-way PCB terminal
block, lead pitch 7.5 mm
F1 = fuse, 4AT (time lag) with PCB
mount holder
TR1 = mains transformer, 12V @ 1.5
VA, short-circuit proof, PCB mount
B1 = B80C1400, round case (80V
piv, 1.4A)
RE1 = power relay, 12V, 2 x c/o,
PCB mount
RE2 = miniature relay, 12V, 2 x c/o,
PCB moun

How does it work?
Almost immediately after switch-on, fast-acting miniature relay RE2 pulls in, since it is connected directly after the bridge rectifier. Its nor-mallyclosed contact then isolates RE1 from the supply, and thus current flows to LA1 via RE1’s normally-closed con-tact. RE1 does not have time to pull in as it is a power relay and thus relatively slow. Its response is also slowed down by the time constant of R1 and C1. If the current through the light switch is briefly interrupted, RE2 drops out immediately. There is enough energy stored in C1 to activate RE1, which then holds itself pulled in via a second, normally-open, contact. If current starts to flow again through the light switch within 1s, LA2 will light. To switch LA1 back on it is necessary to turn the light switch off for more than 3 s, so that C1 can discharge via R2 and RE1. The printed circuit board can be built into a well insulating plastic enclosure or be incorporated into a light fitting if there is sufficient space.
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PCB-Layout

Caution:
the printed circuit board is connected directly to the mains-powered lighting circuit. Every precaution must be taken to prevent touching any component or tracks, which carry dangerous voltages. The circuit must be built into a well insulated ABS plastic enclosure.

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Simple Dual Voltage Power Supply 12 Volt

This is the simple circuit diagram of Dual Voltage Power Supply. It is used for Misc… application. This circuit is called regulated power supply. For this reason the main component of this circuit is Regulator IC. It also needs few components to built. The regulator 7812 is the positive voltage regulator and 7912 is the negative voltage regulator.

Simple Dual Voltage Power Supply 12 Volt Circuit Diagram

You can also use 7809 for 9 volt positive power supply and 7909 for negative voltage power supply. It regulates voltage from 24Volt to 12 Volt (DC). The transformer input is 110Volt to 220Volt (AC) and the output must be between 12Volt to 24Volt (AC) and current must be 500mA. In this circuit some capacitors are used as a filter for removing repole.

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Reliable 6 Watt Hi Fi Audio Amplifier Using TDA2613

A 6 watt audio amplifier circuit using TDA2613 is shown here. TDA2613 is an integrated Hi-Fi  audio amplifier IC from Philips Semiconductors. The IC is switch ON / switch OFF click proof, short circuit proof, thermally protected and is available in 9 pin single in line plastic package. In the given circuit, TDA2613 is wired to operate from a single supply.

Capacitor C4 is the input DC decoupler while capacitors C5, C6 are power supply filters. Input audio is fed to the non inverting input through capacitor C4. Inverting input and Vp/2 pins of the IC are tied together and connected to ground through capacitor C3. Capacitor C2 couples the speaker to the ICs output and the network comprising of capacitor C1 and resistor R1 improves the high frequency stability.
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Reliable 6 Watt Hi Fi Audio Amplifier Circuit diagram

Notes.

• Assemble the circuit on good quality PCB.
• Supply voltage (Vs) can be anything between 15 to 24V DC.
• Heat sink is necessary for TDA2613.
• Do not give more than 24V to TDA2613.

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