Electronic Components blog

Reflex Tester Circuit

2013-04-18T19:22:00.003-07:00

Testing human reaction speed is not only a fun way of spending time, but also allows the drawing of conclusions, for example on the skills of a momentary driver. When the contact closes the power button, the astabil multivibrator built with IC1 produces pulses that are applied to counter IC3. D1 …. D10 LEDs light up sequentially in a chained fast.

Once the person tested acts stop button S2 the astabil multivibrator is blocked, the last ordered with decoder IC4 LED lights next. If frequency of the astabil multivibrator with P1 is adjusted so that the numerator, for example, receives a pulse every 10 seconds, then the reaction time can be read easily. The test can be repeated after drive reset button (S3). Reflex tester circuit absorbs about 120 mA current, supply voltage (5V) must be stabilized. Frequency can be adjusted to the astabil multivibrator with P1 between 10 Hz and 80 Hz.

ICL7650SCPD HIN232CP HD6475328CP10 HFA3783IN LF353M LP2951ACM MAX691ACSE IRF7201 HIN202ECBN LMC555CM MAX856CSA

Reflex Test Circuit Diagram

LASER diode

2013-04-18T19:21:00.003-07:00

Laser is of prime importance in Optical memories, Fiber optic communications, Military applications, Surgical procedures, CD players, Printers etc. Various forms of lasers like Gallium Arsenide laser, Helium Neon laser, Carbon dioxide laser etc are used in various applications. CD players use laser technology to read the optically recorded data in the form o fBits and Pits on the CD.

Laser is a narrow beam of Photonsemitted by specially made laser diodes. Laser diode is similar to an ordinary LED, but it generates a beam ofhigh intensity light. A laser is a device in which a number of atoms vibrate to produce a beam of radiation in which all the waves havesingle wavelength and are in Phasewith each other.

Monochromatic Laser

PS2501-1 MAX706CPA MC10131L LXT907PC H11L1 LM1117MPX-3.3 LT1372CS8 MT8816AP MT8952BE MC34063A LM393DT INA2134UA MAX213ECAI LXT915QC MAX232 ISPLSI1032E-70LT

Laser light is Monochromatic and can be focused as a pencil beamThe beam of a typical laser has 4×0.6mm widening at a distance of 15 meters. Like an LED, laser diode converts electrical energy into light energy.

How it Works?

The most common laser diode generates semiconductor or injection laser. In these lasers, a population of Inversion Electrons is produced by applying a voltage across its p-n junction. Laser beam is then available from the semiconductor region. The p-n junction of laser diode has polished ends so that, theemitted photons reflect back and forth and creates more electron-hole pairs. The photons thus generated will be in phase with the previous photons. This will give a Pencil Beam and all the photons in the beam are Coherent and in phase.

Applications of Laser

Laser diodes can be switched on and off at frequencies as high as1GHz, making them ideal in Telecommunication applications. Since laser generates heat on hitting the body tissue, it is an ideal solution to heal sensitive parts like Retina of Eye and brain. Laser can be used topinpointthe lesions so that nearby tissues are not affected as in the case of surgery.
Laser Diode

A Word of Caution
Laser is a high intensity penetrating beam and is extremely dangerouswhen focused on to the Eye. Low cost Laser pointers are now available in the market and some people handle them carelessly and may even give to children to play with.A Laser pointer with output power higher than 5 mW is harmful. Take utmost care while handling laser diodes. Always take precautionary measures while trouble shooting CD players, Laser printers etc.

USB

2013-04-18T19:20:00.006-07:00

The easiest way to connect computer peripherals is through a Universal Serial Bus. The USB is a plug-and-play interface between the PC and the peripherals. The advantage of USB is that the device can be plugged in or plugged out without the need of restarting the PC. Here explains the working of USB.

USB is the short form of Universal Serial Bus, a standard port that helps to connect computer peripherals like scanner, printer, digital camera, flash drive and more to the Computer. The USB standard supports the data transfer at the rate of 12 Mbps.

USB Specification

Two important aspects of USB are itssupport capability and total bandwidth.USB is capable of supporting127 USB devicesand has a totalbandwidth of 12 Mbit per secondwhich is equal to 1.5 MB per second. Working of a 12 Mbit (full speed device) or a 1.5 Mbit (low speed devices) depends on the total bandwidth of the USB.

USB Connections

Each USB device uses the standardA type USB connector to the USB hostor Hub throughA type receptacle. The other end of the USB cable has seriesB connectorwhich is used to plug into theB type receptacle

A connectoris used for the upstream connection towards the host andB connectorfor the downward stream to the USB device. When the USB device is connected to the PC, it activates the host to recognize it. The PC detects the USB device and manages a control flow between the USB device and computer. PC also manages the data transfer between the USB device and PC. Once detected, the PC sends data to the USB system software to recognize it which then identify the device and assign an address. Thisaddressis used to detect the particular USB device. The software controls the input and output data between the PC and USB device. If the software fails to assign the address, PC will not detect the USB device.

USB Cable

The USB cable provides four pathways- twopower conductorsand two twistedsignal conductors.The USB device that uses full speed bandwidth devices must have a twisted pair D and D- conductors. The data is transferred through the D and D- connectors while Vbus and Gnd connectors provide power to the USB device.

USB Wiring connection

The USB cable has typically four wires to connect the A type connector

Red 5V Pin 1
White D Pin 2
Green D- Pin 3
Black Gnd Pin 4

USB Hub

TheUSB Hubis used to connect many devices to the PC using a single USB connector. The USB Hub can detect the attachment or detachment of devices in each port of the Hub. The Hub also distributes power to all the devices connected to it. Hub also detects low speed and full speed devices.

TheUSB Hubhas two components- AHub controllerand aHub repeater. The Hub controller enables the Hub to communicate with the PC for configuration and control of devices attached to it. The Hub repeater has hardware support for reset, suspend and resume signals.

USB Flash Drive

The most commonly used USB device is theFlash drivethe commonly called Pen drive. It is a mass storage device capable of functioning like a hard disk of computer

Infrared Repeater System circuit

2013-04-18T19:20:00.002-07:00

This infrared repeater system is used to extend the range of an infrared transmitter used at an audio or video equipment at 10 m. The original signal is captured by the infrared receiver (figure 1), amplified and delivered to the IR transmitter (figure 2) through a coaxial cable.Its is possible to control an audio system located in the living room from the dining room so it can be used as an infrared remote repeater.

Although in fig. 1 it is used the BPW34 IR diode you can get good results with BP104. The performances of the IR receiver built on the PCB shown in figure 3 were much better than on a Veroboard.
The receiver consumes a strong current dependent of the digital code used by the remote system and it is between 30 mA and 100 mA.
The power supply lines for T1 and T2 must be kept as short as possible.

Infrared Repeater’s Receiver Circuit Diagram

PCF8576CT OPA541AP PCI1420PDV RTL8139D OPA2130UA PCM1720E SP232ECN OP37GS OPA2134PA OPA2650U
The range of the transmitter depends to some extent by the room in which it is used but under normal conditions should be about 10 meters.
The output signal frequencies may be between 5 kHz and 200 kHz. Special attention should be given to avoid optical reactions between the receiver and transmitter.

IR Repeater’s Transmitter Circuit Schematic

Infrared Repeater PCB Layout

Battery Monitor Circuit

2013-04-17T19:45:00.001-07:00

Here is a simple Battery Monitor circuit for a quick check of 12 voltLead-Acid Battery. Battery charge should be constantly monitored to increase the life of the battery.Overchargeas well asunder chargewill reduce the battery life. The terminal voltage of the Lead Acid battery should be with in the range of 12.5 to 13.5 volts. If the battery voltage reduces below 10 volts for long period, battery will not accept any charging current. Similarly if the terminal voltage exceeds above 14 volts, battery will be destroyed.

The circuit is aZener controlled transistor switchlighting three LEDs Red, Green and Yellow to show battery states likeLow, Normal and High.When the battery voltage is less than 11 volts, Zener diodes ZD1 and ZD2 cease to conduct and Red LED only lights indicating low battery condition. If the voltage is between 12 volt and 14 volts, Zener diode ZD1 forward bias and T1 conducts. The Green LED connected to the collector of T1 lights indicating normal voltage. If the battery voltage exceeds 15 volts, Zener diode ZD2 also conducts and T2 forward bias. This lights Yellow LED indicating over charge. Thus the following indications can be obtained

DS3695AM AM79C970AKC ADV7170KSU ADC0848CCV ADM706SAR AD654JN AD708JN AD7533JN AD847JN EPF10K30RC240-3 BCM5308EKTB EPM7064STC100-7 EPF10K50VBC356-1 AT89S52-24JU AD9560AKR

Battery Monitor Circuit Diagram

Solar Charger Circuit

2013-04-17T19:42:00.002-07:00

Here is a solar charger circuit that is used to charge Lead Acid or Ni-Cd batteries using the solar energy power. The circuit harvests solar energy to charge a 6 volt 4.5 Ah rechargeable battery for various applications. The charger has Voltage and Current regulation and Over voltage cut off facilities.

Solar Charger Circuit Diagram

EPM1270F256C5N EPC2TC32 AD790JR CS82C54-10 ATMEGA32L-8AU AD8138AR AD736JN FDN338P EPM7064SLC84-10 EPF10K30RC240-4 EPF6024AQC208-3

The circuit uses a 12 volt solar panel and a variable voltage regulator IC LM 317. The solar panel consists of solar cells each rated at 1.2 volts. 12 volt DC is available from the panel to charge the battery. Charging current passes through D1 to the voltage regulator IC LM 317. By adjusting its Adjust pin, output voltage and current can be regulated.

VR is placed between the adjust pin and ground to provide an output voltage of 9 volts to the battery. Resistor R3 Restrict the charging current and diode D2 prevents discharge of current from the battery. Transistor T1 and Zener diode ZD act as a cut off switch when the battery is full. Normally T1 is off and battery gets charging current.

When the terminal voltage of the battery rises above 6.8 volts, Zener conducts and provides base current to T1. It then turns on grounding the output of LM 317 to stop charging.

UM3561 Siren Generator Design

2013-04-17T19:41:00.002-07:00

UM3561 is an excellentROM ICthat can generate Multi siren tones simulating Police siren, Ambulance siren, Fire brigade siren and Machine gun sound. This 8 pin low power IC can work down to 2.4 volts.

The UM 3561 is a low cost siren generator designed for use in toy applications. The IC has an inbuilt oscillator and tone selection pins. It is easy to make a siren generator with only a few external components. Only one external resistor and a speaker driver transistor are sufficient to make a simple siren generator.
IRF830 LT1361CS8 MAX843ISA LP2951CM LM2903 LT1399CS INA132U MAX3241CAI EPF10K30RC208-3 EPM7032AETI44-7

Inside the UM3561
Inside the IC, there is an oscillator circuit and the frequency of oscillations is controlled by the external resistor connected to OSC 1(Pin 7) and OSC2 (Pin 8). A 220 K resistor will give satisfactory results. The oscillations thus generated will be then transferred to a control circuit which function based on the tone selection through the connections of SEL 1 (Pin 6) and SEL2 (Pin 1) . The control circuit passes the signal to an address counter and then to the ROM. The tone pulses thus generated will be available from the output pin 3. Since the sound is weak, an amplifier is necessary to get loud sound. A single NPN transistor will amplify the sound.

Pin Assignment

Pin 1 Tone Sel.2
Pin 2 Gnd
Pin 3 Output
Pin 4 NC- Used for testing purpose
Pin 5 3V
Pin 6 Tone Sel .1
Pin 7 Osc 1
Pin 8 Osc 2

Tone Selection

By changing the pin connections of Sel.1 (Pin6) and Sel. 2(Pin 1) it is easy to change the siren tones.
Sel 1Sel 2Tone
Pin 6 Pin 1
NC NC Police siren
3V NC Fire Engine sound
Gnd NC Ambulance Siren
NC 3V Machine Gun sound

UM3651 Siren Generator Circuit Diagram

Voltage to Frequency Converter Circuit

2013-04-17T19:40:00.000-07:00

This voltage to frequency converter circuit has an oscillator that is voltage controlled and has a small, 0.5% deviation. IC1 function as a multivibrator and produces rectangular impulses with equal width.
The width of the impulses depend on R4, P1 and C1. With P1 we can do fine adjustments of the output frequency.

The output frequency can be easily adjusted with the help of U1 voltage. D3 diode is required because we want to eliminate R4 and P1 influence. D1 and D2 diodes produce a small flow of temperature. With P2 we adjust the offset voltage. Because of its high quality, this voltage-frequency converter (VCO) can be used in a large field of applications.

Voltage-Frequency Converter Circuit Diagram

MC145026P LM1851N LTC485CN8 LTC3707EGN LTC1753CG LT1014DN LM2596S-3.3 HC9P5504B-5 MAX913CSA MAX707ESA M82C55A-2 MAX483CSA IS41C16256-35K

Pest Repeller Circuit

2013-04-16T19:03:00.006-07:00

The two timers in the bug repeller have some interesting characteristics. Roth of them have their thresholds externally set; the oscillator on the left

LM139J MPC508AP MAX668EUB MAX695CWE L4978D LM3578AM LM380N LM2574M-ADJ DAC0800LCN AT45DB041D-SU has a 50% duty cycle and the oscillator on the right acts as a VCO.

Canary Sound Simulator Circuit

2013-04-16T19:03:00.002-07:00

This circuit generates the sound of two canaries singing in a cage. Two LM324 quad amps make up seven oscillators. One oscillator is an on/off control, the other six generate the sounds of two canaries.

MC68160FB MC145572PB MAX767CAP lm308ｎ LM2901M MAX3510EEP MC145406P ICM7218AIJI MAX3232CWE MC145503DW MAX813LCPA M12L16161A-7T MAX153EAP LM4871MX

Ultrasonic-transceiver

2013-04-16T19:02:00.004-07:00

This ultrasonic transmit/receive circuit operates at 40 kHz.

Ultrasonic-pest-repeller

2013-04-16T19:02:00.001-07:00

This circuit is a 555 timer IC connected as a square-wave generator. Its base frequency is approximately 45kHz, as detennined by the values of Rl, R2, and Cl. The 45-kHz carrier is frequency modulated by a modified trapizoidal voltage waveform applied to pin 5 of the 555 timer. That modulating voltage is developed by a network consisting of C2, R3, and R4 connected across one leg of the bridge rectifier. The sweep is approximately 20kHz on each side of the base frequency.

The speaker is a 2-inch piezoelectric tweeter.

Step Down Transformer

2013-04-15T19:12:00.003-07:00

A step-down transformer is one whose secondary voltage is less than its primary voltage. It is designed to reduce the voltage from the primary winding to the secondary winding. This kind of transformer “steps down” the voltage applied to it.
As a step-down unit, the transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. The primary winding, which doesn’t have to conduct as much current, may be made of smaller-gauge wire.

Jump to chapter:

Step-Down Tranformer Considerations
how to wire a step down transformer
how to check a step down transformer

Step-Down Tranformer Considerations

It is possible to operate either of these transformer types backwards (powering the secondary winding with an AC source and letting the primary winding power a load) to perform the opposite function: a step-up can function as a step-down and visa-versa.

One convention used in the electric power industry is the use of “H” designations for the higher-voltage winding (the primary winding in a step-down unit; the secondary winding in a step-up) and “X” designations for the lower-voltage winding.

DA82562ET GD82559 AD724JR DS2154L DS1232 ADS774JU DP83816AVNG DS1302S EPF10K10QC208-3 AD9883AKST-140 ADM706AR EPM7128ATC100-10 FDS6975 ADS1210U AD558JN EPM7256AEFC256-7 EPM7256AEQC208-10 EPM7064LC68-15 One of the most important considerations to increase transformer efficiency and reduce heat is choosing the metal type of the windings. Copper windings are much more efficient than aluminum and many other winding metal choices, but it also costs more. Transformers with copper windings cost more to purchase initially, but save on electrical cost over time as the efficiency more than makes up for the initial cost.

Step-down transformers are commonly used to convert the 220 volt electricity found in most parts of the world to the 110 volts required by North American equipment.

How to Wire a Step Down Transformer

Observe and identify the schematic and rating of the step down transformer to be installed. Remove the terminal connection box cover placed at the lower side of the transformer. Only the high amperage types will have this enclosure, while lower powered transformers will have an exposed screw terminal.
Know termination identification follows for all step down transformers: H1, H2, H3 and H4 signify the high voltage side or power feed end of the transformer. This holds true regardless of the size of the transformer. Interconnection of the transformer will vary depending on the manufacturer and voltage used for feeding the transformer.
Terminate the feed power wires first by cutting the wires to length. If you are using large wire lugs be sure to take into consideration the length of the lug and the amount of wire that can be inserted into the female crimp area.
Strip back the outer insulating of the wires with the pocketknife or wire strippers. Insert the eye ring or wire lug over the bare copper wire and crimp the connection device, using the appropriate-size crimper, permanently to the wire.
Terminate the high side, high voltage of the step down transformer. If the high side terminals are bolts, be sure to follow any torque requirements that are listed by the manufacturer.
Terminate the low side, low voltage of the transformer. Note these terminals will be identified by X1, X2, X3 and X4. Again follow the manufacturer’s individual schematics for that particular type of transformer. Note that on small control transformers there will only be an X1 and X2. X1 is the power or “hot” side and X2 is generally the grounding and neutral portion of the low voltage.
Terminate the small control transformer for X1 and X2. X1 will go directly to the control circuit after passing through a small fuse that is rated for the circuit. X2 will be terminated not only to the neutral side of the control circuit, but the grounding safety as well. In other words, the X2 side of the small control transformer must be tied to the grounding system of the electrical circuit.
Replace all covers on the transformer and any enclosures that protect you from electricity. Apply the high voltage to the transformer by switching on the feeder power circuit. Turn on the low side safety circuit control.
Use a volt meter to test for proper voltage on the step down side of the transformer. It should be the same that is listed on the specs tag provided by the manufacturer.

How to Check a Step Down Transformer

Remove all wires from the transformer terminals using the screwdriver. Identify the wires if they are not already identified. Use a clear tape and pen. Write the terminal that the wires are attached to and place the identified tape on the wire’s end.
Turn the volt ohmmeter to the “Ohms” position and place the red lead into the connector identified as “Ohms.” Touch the black lead to the metal frame of the transformer.
Touch the red lead to the transformer’s terminals in the following order: H1, H2, X1 and then X2. The meter should read infinite ohms or wide open. Infinite ohms on a digital meter will be identified as a blank screen or a wide open will have the word “Open” displayed. If the meter registers any form of resistance, there is an internal problem with the windings. The copper coils may be shorted to the metal frame of the transformer. The transformer will have to be replaced.
Check the continuity of each separate coil using the ohmmeter. Touch the black lead to H1 and the red lead to H2. The meter should give a resistance reading. Generally, it should read in the range of 3 to 100 ohms, depending on the style and type of transformer. Perform the same test to the X1 and X2 terminals. You should receive the same results. If the meter reads infinite ohms or a wide open when checking between the terminals of the same coil, the wires are broken. Replace the transformer.
Use the ohmmeter to conduct the transformers isolation circuit. Touch the red lead to H1 and the black lead to X1. The meter should read infinite ohms or a wide-open circuit. Perform the same test, but to H2 and X2 respectively. If any resistance at all is read on the meter other than a wide-open circuit, the isolation of the transformer has been compromised and must be replaced.

Electronic Metronome circuit schematic

2013-04-15T19:11:00.002-07:00

This metronome circuit schematic is not modern but is cheap and reliable. The well known 555 is presented in this metronome circuit and produces regulated impulses which can be heard at a speaker. The metronome frequency can be adjusted with P1. The power supply is a 9V battery and if you use a 8Ω speaker insert a 33 – 100Ω / 1W resistor in series.

Metronome circuit schematic diagram

LM78L05ACM ISO124P MIC2558BM MAX233CPP MAX3221ECAE MAX488CSA LMC662CM LM2575T-ADJ MAX705CPA HIP6004BCB LM393P

Solar Powered Animal Scarer

2013-04-15T19:10:00.002-07:00

Here is a solar powered Flasher to scare away the nocturnal animals like bats and cats from the farm yard or premises of the house. The brilliant multicolored flashes confuse these animals and they avoid the hostile situation. It is fully automatic, turns on in the evening and turns off in the morning.

The circuit has an LDR controlled oscillator built around the Binary counter IC CD 4060.The functioning of the IC is controlled through its reset pin 12. During day time, LDR conducts and keeps the reset pin of IC high so that it remains dormant. During night, LDR cease to conduct and the reset pin will be grounded through VR1. This triggers the IC and it stats oscillating using the components C1 and VR2. Output pins 7, 5 and 4 are used to power the LEDs strings. VR1 adjusts the sensitivity of LDR and VR2, the flashing rate of LEDs. High bright Red, Blue and White LEDs are used in the circuit to give brilliant flashes. Red LEDs flash very fast, followed by blue and then White. White LEDs remains on for few seconds and provide light to a confined area. More LEDs can be added in the strings if desired. The circuit can also function with 12 volt DC.

Animal Repellent Circuit Diagram

HDMP-1646A MAX1714AEEP L6561 LM567CN LM2902N MIC2562A-1BM MAX798ESE MMBT3904 MIC5209BM MAX202CPE MAX238CNG LXT972ALC MAX208CWG LMC662AIM

The circuit uses a solar powered battery power supply. During daytime, battery charges through R1 and D1.Green LED indicates the charging mode. During night time current from the solar cell decreases and D1 reverse biases. At the same time D2 forward biases to provide power to the circuit. Resistor R1 restricts the charging current and the high value capacitor C1 is a buffer for current.

Animal Scarer Solar Power Supply

Full duplex audio line circuit

2013-04-15T19:09:00.002-07:00

This full duplex audio line circuit enables two audio signals in opposing directions to flow simultaneously through a common twisted pair line. And it does that without complicated communication technology. This technique called full duplex is not really new. It is common in telephone technology. However, the telephone uses a carrier signal. This circuit on the other hand does the trick without a carrier signal.

The principle is simple: two transmitters, each one attached at each end of the line, feed the signals. The voltage at the line will be the sum of the two signals: U1 U2. In the actual circuit however, this is equivalent to only the half of the sum. At each end of the line, the signal is recovered while the other signal gets rejected. This requires that two identical circuits must be constructed.

TL074CN TMS320VC5409PGE100 TDA1308 TMS320LF2406APZA REF02AU OPA4227UA SN74LVC1G08DCKR OP177G LM337LM MAX211CWI MAX213CAI LM4880M The opamp A1 works as an impedance converter and at the same time functions as the transmitter. The resistor R5 protects the output of A1 from the signals coming from the transmitter at the other end of the line. The sum of the signals is taken from the output of the circuit and fed to the non-inverting input of the differential amplifier composed of the opamps A2, A3 and A4.

The “right” signal goes through the voltage divider network made of R4, R11 and P1. It is then taken out from the sum of the signals. This “right” signal appears at the OUT output of the circuit.
The resistors must be low tolerance type to achieve the highest same phase suppresion possible. This suppresion is about 80 dB at 1 kHz and 60 dB at 20 kHz. When using long cables, the suppresion can be improved by adjusting C3.

Full duplex circuit diagram

Calibration: Connect the (IN) input to a signal generator and feed a sinus wave of 5 kHz with 1 Veff to the circuit. Attach the twisted pair line (cable) to the (IN/OUT) point of the circuit and short the input of the second circuit at the opposite end of the cable. Raise the signal frequency to 10 kHz and adjust C3 to get the best result.

Crystal quartz oscillator circuit

2013-04-15T19:07:00.002-07:00

Another great quartz crystal oscillator schematic with bb139, a 2-nd harmonic quartz crystal and one BF214 transistor. So, the Q quartz is half of the desired transmitter frequency, L1 has 24 turns, 0.08mm ? built on a 455kHz carcase. L2 has 8-9 turns / 0.8mm ? / 5mm ?. Thisquartz oscillator circuithas a great frequency stability, I’ve build it.
Crystal quartz circuit components
R1 = 10K
R2 = 100K
R3 = 8.2K
R4 = R6 = 820
R5 = 15K
C1 = 330nF
C2 = 1nF
C3 = 1.5pF
C4 = 15pF
C5 = 2.2nF
C6 = 6 – 25pF trimmer
C7 = 4.7pF
D1 = BB139
D2 = 5.6v zenner diode
T = BF214
Q = half frequency quartz crystal

Crystal quartz oscillator circuit schematic

78L05 74HC4053D XC95288XL-10PQ208C TL7705ACP TLP521-2 UDN2981A

Sound Activated Switch circuit

2013-04-11T22:39:00.003-07:00

With this sound activated switch, control by sound may be very useful, not just on a robot but also for a bit of home automation, for example a sound-activated light responding to a knock on the door or a hand clap. The light will be automatically switched off after a few seconds. An alternative use is burglar protection — if someone wants to open the door or break something the light will come on, suggesting that someone’s at home.
The circuit can work from any 5–12 VDC regulated power supply provided a relay with the suitable coil voltage is used.

When you first connect the supply voltage to thesound activated switchcircuit, the relay will be energised because of the effect of capacitor C2. Allow a few seconds for the relay to be switched off. You can increase or decrease the ‘on’ period by changing the value of C2. A higher value results in a longer ‘on’ period, and vice versa. Do not use a value greater than 47 μ F.

Biasing resistor R1 determines to a large extent the microphone sensitivity. An electret microphone usually has one internal FET inside which requires a bias voltage to operate. The optimum bias level for response to sound has to be found by trial and error. All relevant electrical safety precautions should be observed when connecting mains powered loads to the relay contacts.

Sound activated switch circuit diagram

LM2576T-ADJ DS90LV031ATM AD820AR ADM232LJR ADM705AR BAV70 DG508ACJ EPM7128STC100-10 EPM7064SLC44-10 74HCT14D UC3844N TDA2822M UC3842AN OPA177GS NE558D

50Hz Ripple filter circuit

2013-04-11T22:37:00.003-07:00

The ripple filter circuit is specially deisgned to filter out 50 Hz ripple signals from audio lines. A 50 Hz noise is usually found in european countries. In many cases, it is not possible to remove the cause of ripple noise. The featured active filter notch filter solves the problem in suvh cases. It allows the desirable signal to pass through with minimal attenuation. The Q factor of the filter is 10 at the inductivity value of 150 H.

These values can only be achieved practically by using an electronic “coil” such as this circuit. The circuit works as an active RCL circuit. The two opamps Ai and A1 LF356A together with the resistors R2 to R5 , C2 and P1, work as the electronic “coil”. The coils inductivity value is L = R2 x R3 x C1. Potentiometer P1 varies the inductivity value. The filter circuit attenuates the ripple noise by 45 to 50 dB, if properly adjusted.

Ripple filter circuit diagram

Preprogrammed single-chip microcontroller

2013-04-10T18:29:00.002-07:00

Twenty-five musical keys and 25 LEDs are provided to denote F to F` with half notes in between. Memory can store a played tune. There are ten preprogrammed tunes (each has an average of 55 note s) masked in the chip. Any tune can be recalled by depressing the Tune Button followed by the corresponding Sharp Key

In learn mode, the player can learn the ten preprogrammed tunes.
EPF6016QC208-3 AD817AR DG211CJ EPM7192SQC160-10 FDS6612A AD9850BRS AD8016ARB TMS320F2812PGFA PCF8584T SN75176BP PCM1801U PCI9080-3 MAX211ECAI MAX708CSA

Fet Amplifier With Offset Gate Bias Circuit

2013-04-10T18:28:00.002-07:00

In this amplifier circuit, the gate of the MPF 102 is biased with an external voltage.

This circuit achieves tighter control of the operating point and biasing conditions.
Source: http://www.hqew.net/circuit-diagram/Fet-Amplifier-With-Offset-Gate-Bias-Circuit_14875.html

Mini Stereo Amplifier Circuit

2013-04-10T18:27:00.001-07:00

Using a Thomson TEA2025, this stereo amplifier provides 1 W per charuiel into 4 with a 9-V supply. Input sensitivity is 25 mV p-p for full output.

Note that pins 4, 5, 12, and 13 of TCI should be effectively grounded to a ground plane and heatsinked.

Biquad-audio-filter

2013-04-10T18:25:00.003-07:00

This universal filter offers low-pass, high-pass, bandpass, band elimination, and all-pass functions. The Biquad consists of two successive integration stages followed by an inverting stage. The entire group has a feedback loop from the front to the back consisting of Rl which is chiefly responsible for controlling the center frequency, W 0. The first stage of integration is a poor integrator because R2 limits the range of integration. R2 and C form the time constant of the first stage integrator with R3 influencing gain H almost directly.

AD826AR EPM7128SLC84-15 ATMEGA8L-8AU AD9883AKST-110 EPM3032ATC44-10 AD9884AKS-140 DG412DY FDS4435 SP3243ECA SAA7111AHZ SAA7118E The band-pass function is taken after the first stage with the lowpass function taken after the third stage. The remaining filter operations are generated by various combinations of three stages. The Biquad is orthogonally tuned, meaning that W 0, Q, and gain H can all be independently adjusted. The component values known will allow W 0 to range from 40 Hz to 20 kHz. The other component values give an adequate range of operation to allow for virtually universal filtering in the audio region. W 0, Q, and gain H can all be independently adjusted by tuning Rl through R3 in succession.

Lamp

2013-04-07T18:26:00.003-07:00

Why a lamp tester or fuse tester? Testin cables, wires, lamps… belongs to a repair job and sometimes this becomes too cumbersome since one has only two hands and too often, one has to hold the part being tester and the two probes of an ordinary continuity tester all at the same time.

This fuse and lamp tester enables easy testing of lamps and fuses by using the conductivity of the human body. One of the test probes is connected to the part under test while the other probe is hel dby the normal hand.

When the lamp or fuse is working properly, your eyes will glow in the dark! Just kidding. When the lamp or fuse is working properly, a small amount of current flows through the hand which is enough to switch the transistors and light the LED.

Tester for fuse and lamp

Speaker balance indicator circuit

2013-04-07T18:25:00.004-07:00

You may use this speaker balance calibrating circuit when using a stereo amplifier, there are many possible mechanical problems that may influence the amplifier’s output performance. The usual culprit is the mechanical potentiometers which are not rarely unsync in their stereo resistance pads. This results to unbalanced volume levels on the audio channels. Most good stereo units have a balance control to compensate for this imbalance.

In using this balance indicator circuit, its left and right input channels are connected to the corresponding speaker outputs of the amplifier. Identical signals are then fed to the amplifier’s stereo inputs. When a signal of exactly the same amplitude is coming out from both speaker outputs, the meter M of the speaker balance circuit will stay at its zero setting. The meter M is a type with a zero setting at the middle of the scale. This enables one to see at first glance when one channel is louder than the other channel

Calibrating the speaker balance indicator circuit

Inject a signal in one channel and set the amplifier’s volume to maximum.
While doing this, turn the potentiometer P1 until the meter swings to end of the scale in the direction of the channel.