Top Circuits Page 169
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Here is a very simple, inexpensive and interesting project which provides lot of fun to a home experimenter or hobbyist. This simple transmitter can transmit speech over a short range. It can be used as a simple cordless microphone. The circuit uses two....
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If you are working at frequencies of the order of 850MHz to 4GHz andnd that a frequency multiplier is required, the HMC 187, HMC 188 and HMC 189 (see table) frequency doubler may be just the solution you are looking for. The isolation performance of these....
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Commonly used 3-pin linear voltage regulators, for example the LM317, cannot handle input voltages in excess of about 30V. The LR8A from Supertex Inc is a new, adjustable three pin regulator that can accept input voltages up to 450V and can supply an output....
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The detector is intended for the recognition of obstructions at distances of a few millimeters to a few centimeters. Similar detectors are used in the industry and health services, for instance, to open a water tap via a magnetic valve. The sensor, IC2, is a....
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This little circuit is invaluable for quick go/no-go testing of just about any remote control transmitting infra-red (IR) light. The tester is battery-powered, built from just a handful of commonly available and inexpensive parts, and fits in a compact....
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This circuit can be built from readily available low-cost components, some of which may even be hiding in your junk-box! The indicated value of 22 for resistor R1 causes an average current of about 65mA through infrared emitter D1. Because the IRED is....
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The input resistance of a. c. -coupled op amp circuits depends almost entirely on the resistance with which the d. c. setting is determined. If CMOS op amps are used, the input resistance is normally high, currently up to 10 M. If a higher value is needed, a....
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With many audio systems consisting of separate units, you`ll oftennd that due to economic reasons only the amplifier has a remote control receiver module. The control signals are then sent to the other units using patch cables. The tuner and CD player, for....
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Many modern motherboards are equipped with an infrared data interface compliant with the IrDA standard, but this interface not very often used. However, it is not difficult to build a data transmission module and connect it to the corresponding header. As....
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This circuit uses standard components and shows a method of indicating the fuse status of mains powered equipment while providing electrical isolation from the mains supply. A standard miniature low power mains transformer (e. g. with an output of around 6 V....
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A lambda probe (or oxygen sensor) can be found on the exhaust system of most cars running on unleaded fuel. Having reached its normal operating temperature (of about 600 degrees Celsius!) the lambda probe supplies an output voltage proportional to the amount....
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In many projects use is made of alphanumeric LCDs that are driven internally by Hitachi`s industry-standard HD44780 controller. These displays can be driven either in 4-bit or 8-bit mode. In the first case only the high nibble (D4 to D7) of the display`s....
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The circuit described here counts the number of times that an infrared beam is interrupted. It could be used to count the number of people entering a room, for instance, or how often a ball or another object passes through an opening (handy for playing....
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This circuit ensures that you will never again forget to switch on the lights of your car. As soon as the engine is running, the dipped beams and the sidelights are automatically switched on. The circuit also causes the dipped beams to be extinguished as....
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Liquid-crystal displays come in all sorts and sizes, and this applies also to their pinouts. In fact, many of these displays cannot be used properly without the manufacturers` documentation. But, of course, this can never be found when it is needed, and a....
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The signal from a microphone is two weak for a standard line input. This low-noise DC-coupled microphone amplifier provides a solution for anyone who wants to connect a microphone to his or her hi- installation. As can be seen from the schematic diagram, a....
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Many circuits can be powered directly from the mains with the aid of a series capacitor (C1). The disadvantage of this approach is that usually only one half cycle of the mains wave-form can be used to produce a DC voltage. An obvious solution is to use a....
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Often you find yourself in the position of needing to wind your own coil for a project, or maybe you come across an unmarked coil in the junk-box. How can you bestnd out its inductance An oscilloscope is all you need. Construct a resonant circuit using the....
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The design of the charger is similar to that of many commercially available chargers. The charger consists of a mains adaptor, two resistors and a light-emitting diode (LED). In practical use, this kind of charger is perfectly all right. Resistor R1 serves....
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How often on average do you have to call members of your family each day to tell them that dinner is ready, it`s time to leave, and the like The person you want is usually in a different room, such as the hobby room or bedroom. A powerful buzzer in the room,....
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Fans in PCs can be objectionably loud. In many cases, the amount of noise produced by the fan can be considerably reduced by lowering its speed. Although this will decrease the amount of cooling, this need not be a problem as long as you don`t go overboard....
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The pulse width of the compact pulse cum frequency modulator can be varied by altering the change-over point of comparator IC1 with a control voltage via resistor R1. The hysteresis of the IC is determined by resistors R3 and R4. The control voltage also....
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If you ever thought of experimenting with pulse-width modulation, this circuit should get you started nicely. We`ve kept simplicity in mind and used a dual 555 timer, making the circuit a piece of cake. We have even designed a small PCB for this, so building....
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Dedicated model rail enthusiasts using sophisticated train and points controllers often have the problem that as their layouts get bigger and more complex, the transformer supplying power to the points does not have enough current to switch several points at....
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Not only on ecologically grounds but also economically it makes sense to collect rainwater for use in the garden and increasingly for `grey water` domestic use. People who take rainwater collection seriously use large underground tanks for storage. The....
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The designer of this circuit had fitted two (waterproof) loudspeakers in his bathroom and connected them to the stereo system in the living room via a long cable. Naturally, this promptly led to the desire to be able to use the remote control unit from the....
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The circuit diagram shows two LT1398`s from Linear Technology used to create buffered color-difference signals from RGB (red-green-blue) inputs. In this application, the R input arrives via 75 coax. It is routed to the non-inverting input of amplifier IC1a....
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Since modern sound systems usually lack inputs for record players, separate MD preampliers are becoming increasingly popular. They are needed not only by people who still regularly like to listen to vinyl records, but also by those who want tonally....
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In order to measure the RMS value of an alternating voltage an accurate converter is required to produce the true RMS value of its alternating input as a DC output. With simple sine-wave inputs the RMS voltage can simply be calculated as 0. 707 times the....
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An electrically operated rolling shutter usually has a standard control panel with a three-position switch: up, down and stop. If you would like to automate the opening and closing with a time controlled switch, a few additional wires will have to be....
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The best way to measure the current in a circuit is to place a sense resistor in the current path. The higher the resistance, the more exact the measurement will be. However, the drawback of a high resistance is that it affects the operation of the circuit....
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This converter may help if just the serial port on a personal computer is free, whereas the printer needs a parallel (Centronics) port. It converts a serial 2400 baud signal into a parallel signal. The TxD line, pin 3, CTS line, pin 8 and the DSR line, pin....
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Phonographs are gradually becoming a rarity. Most of them have had to yield to more advanced systems, such as CD players and recorders or (portable) MiniDisc player/recorders. This trend is recognized by manufacturers of audio installations, which means that....
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This simple circuit helps you sniff out RF radiation leaking from your transmitter, improper joints, a broken cable or equipment with poor RF shielding. The tester is designed for the 2-m amateur radio band (144-146 MHz in Europe). The instrument has a....
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This circuit provides a simple means to determine the voltage of a low-impedance voltage source. It works as follows. P1, which is a 1-W potentiometer, forms a voltage divider in combination with R1. The voltage at their junction is buffered by T1, and then....
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With extended periods of bright sunshine and warm weather, even relatively large storage batteries in solar-power systems can become rather warm. Consequently, a circuit is usually connected in parallel with the storage battery to either connect a high-power....
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Dynamic‚ip-‚ops ignore pulses at their inputs that are shorter than 40 ns or do not have TTL levels. This means that TTL flip-flops are poorly suited to capturing noise pulses having unknown durations and magnitudes. Anyone who has ever tried to observe very....
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If a transistor junction operating in Zener breakdown is used as a noise source, the amplitude of the noise signal is asymmetric. This problem can be solved by using two transistors as two independent noise sources. One of these has a series resistor to....
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Depending on local regulations and the telephone company you happen to be connected to, the voltage on a free telephone line can be anything between 42 and 60 volts. As it happens, that`s sufficient to make a diac conduct and act like a kind of zener diode....
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Manufacturers of cordless drills generally recommend a battery charging time of three hours. Once the charging time is up the battery must be disconnected from the charger: if you forget to do this there is a danger of overcharging the battery. This circuit,....
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The continuity tester can distinguish between high-, medium-, and low-resistance connections. When there is a conductance between the inputs, which are linked to small probes, a current flows from the +9 V line to earth via R1 and R2. The consequent....
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The circuit in the diagram is a very handy tool for rapidly checking all kinds of thyristor (SCR, triac, ). In case of a triac, all four quadrants are tested, which is done with S3, while in case of a standard thyristor, a positive power supply and trigger....
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This super-simple dimmer consists of only two components, and it can easily be built into a mains switch. If you do this, don`t forget torst switch off the associated branch circuit in the fuse box, since the mains voltage is always dangerous! The circuit....
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Remote temperature measurements have to be linked by some sort of cable to the relevant test instrument. Normally, this is a three-core cable: one core for the signal and the other two for the supply lines. If the link is required to be a two-core cable, one....
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Nowadays, a switch-off delay for the vehicle interior lighting is a naturally a standard feature. However, with certain models having only spartanttings, or older-model vehicles, you`re left sitting in the dark as soon as you climb in and close the door.....
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The video amplifier in the diagram is a well-known design. Simple, yet very useful, were it not for the ease with which the transistors can be damaged if the potentiometers (black level and signal amplitude) are in their extreme position. Fortunately, this....
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The reception of 2 metre signals is generally with a converter and short wave receiver, preferably of communications type. The latter will have sensitivity and selectivity better than average. With such an arrangement of equipment, the 144MHz or other VHF....
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Crowbar circuits are so-called because their operation is the equivalent of dropping a crowbar (large steel digging implement) across the terminals. It is only ever used as a last resort, and can only be used where the attached circuit is properly fused or....
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Figure 36 is the circuit of a preamplifier with high impedance input and an output circuit allowing coupling to a main amplifier. It will be found extremely useful for purposes such as boosting the signal from a crystal microphone. The input socket,....
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The circuit in the diagram enables a negative voltage to be derived without the use of integrated circuits. Instead, it uses five n-p-n transistors that are driven by a 1 kHz (approx) TTL clock. When the clock input is high, transistors T1 and T2 link....
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As readers will know, there are already several power amplifier projects, two using IC power amps (aka power opamps). Both have been popular, and this project is not designed to replace either of them. However, it is significantly smaller than the others, so....
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Any electronics amateur still in possess of a collection of vinyl recordings and aiming at a high quality reproduction should build this preamp and add it to the Modular Preamplifier chain. This circuit features a very high input overload capability, very....
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The transformer is a 220V to 12V, 50Hz and 3. 6VA PCB type transformer. The model seen in the photo is HRDiemen E3814056. Since it is encapsulated, the transformer is isolated from the external effects. A 250V 400mA glass fuse is used to protect the circuit....
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This is yet another project born of necessity. It`s a simple circuit, but does exactly what it`s designed to do - dim LED lights or control the speed of 12V DC motors. The circuit uses PWM to regulate the effective or average current through the LED array,....
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The halogen or krypton bulbs in modern torches (USA and Canada: flashlights) have a limited life and are not particularly cheap. A simple modification in the torch lengthens the life appreciably. It is a fact of nature that any incandescent bulb has anite....
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Any stepper motor can be used as a generator. In contrast to other generators, a stepper motor produces a large induced voltage even at low rotational speeds. The type used here, with a DC resistance of 2G—60 per winding, can generate more than 20 V when....
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The Analog Devices ACP3610 is a voltage doubler that works with a switched-capacitor converter, using the push-pull principle. The switching frequency at the output is approximately 550 kHz. The term push-pull` refers to the two charge pumps, which work in....
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Operation is from a 12v or similar supply, and R1 can be changed if necessary for higher voltages. In this and similar circuits there is considerable latitude in the choice of values for positions such as C1. At B VR1 is a top cut control, and VR2 the volume....
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It is often convenient to be able to fade in or out or mix at any wanted level the inputs from two audio sources. The circuit in Figure 37 is suitable for this purpose. One input is to socket 1, and the second to socket 2. Each input is suitable for high or....
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This little project came about as a result of a design job for a client. One of the items needed was a mic preamp, and the project didn`t warrant a design such as the P66 preamp, since it is intended for basic PA only. Since mic preamps are needed by people....
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If you want to connect a video signal to several destinations, you need a distribution amplifier to match the 75-ohm video cable. A distribution amplifier terminates the incoming cable in 75 ohms and provides several outputs, each with 75-ohm output....
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This is anti theft alarm with wireless connectivity, called Anti Theft Car wireless alarm The FM radio-controlled anti- theft alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF, FM transmitter is fitted in the vehicle at....
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The aboriginal accessory forms a archetypal oscillator ambit whose achievement is both a triangle waveform arresting and a aboveboard beachcomber signal. The triangle arresting is baffled to a accepted regulator circuit, which converts the triangle voltage....
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The following method allows the timer to be triggered by a normally closed switch. This would be useful in applications such as intrusion alarms where the protection circuit is broken if a window or door is opened Trigger Input Control Of 555 Timers ..
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about-face S1 momentarily. This beating acts as a alarm beating for the decade adverse (IC2) which advances by one calculation on anniversary alternating alarm beating or the advance of about-face S1. Ten presets (VR1 through VR10), set for altered ethics by....
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You need this schematics. Go to THIS page and you will find a good pre-amp and power amplifier for your guitar include the complete explanation of its works, and how to build the box. ..
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This circuit can be used where a high current is required with a low-ripple voltage (such as in a high-powered class AB amplifier when high-quality reproduction is necessary). Q1, Q1 and R2 can be regarded as a power Darlington transistor. ZD1 and R1 provide....
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Here is the circuit diagram of a guitar preamplifier that would accept any standard guitar pickup. It is also versatile in that it has two signal outputs. A typical example of using a pick-up attached to a guitar headstock is shown in Fig. 1. The pickup....
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This Digital Circuit describes a Digital Blood Pressure Meter concept which uses an integrated pressure sensor, analog signal-conditioning circuitry, microcontroller hardware/software and a liquid crystal display. The sensing system reads the cuff pressure....
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The program in the microcontroller knows two protocols; the one wire bus used by the DS1820 temperature sensor, and the serial protocol expected by your computer. Once power is applied, the program fetches data from the sensors and sends it to the serial....
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The mini condenser microphone converts sounds into an electrical signal. Resistor R1 provides bias for the condensor microphone`s internal amplifier transistor. The 2N3906 PNP transistor acts as a low noise microphone input amplifier. The 10K gain....
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The 10K resistor (*) is only required if you want the receiver to mute (squelch) under no-signal conditions. You could add a 100K in series with this resistor to get an adjustable squelch. This circuit will JUST drive a crystal earphone or high impedance....
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A number of people have been unable to find the transformer needed for the Black Light project, so I looked around to see if I could find a fluorescent lamp driver that does not require any special components. I finally found one in Electronics Now. Here it....
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The circuit presented here can be used for connecting two telephones in parallel and also as a 2-line intercom. Usually a single telephone is connected to a telephone line. If another telephone is required at some distance, a parallel line is taken for....
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Using this circuit you can convert the 12V dc in to the 220V Ac. In this circuit 4047 is use to generate the square wave of 50hz and amplify the current and then amplify the voltage by using the step transformer. The basic formula is P=VI and between input....
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This circuit uses a complementary pair comprising NPN metallic transistor T1 (BC109) and pnp germanium transistor T2 (AC188) to detect heat (due to outbreak of fire, etc) in the vicinity and energise a siren. The collector of transistor T1 is connected to....
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The terminal of R7 bearing an arrow must be connected to the desired output pin of IC2 or IC3 in order to select the number of LEDs or clusters forming the bar. For example: if you want to drive seven LEDs or clusters connect R7 to pin#11 of IC2 (Output 8)....
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Circuits of this kind are intended to drive LED Arrays in order to create more visibility and conspicuity when a vehicle is stopped or stopping. This circuit, in particular, will emit a visual alerting signal of 4 short flashes, followed by a steady on light....
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Here`s a clap switch free from false triggering. To turn on/off any appliance, you just have to clap twice. The circuit changes its output state only when you clap twice within the set time period. Here, you`ve to clap within 3 seconds. The clap sound sensed....
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Normally the base of a cordless phone has an adaptor and the handset has Ni-Cd cells for its operation. The base unit becomes in-operative in case of power failure. Under such conditions, it is better to provide a backup using Ni-Cd cells externally. Here is....
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Here is a deluxe version of the simple charge rate limiter, using the same idea but with the ability to charge two packs simultaneously from a single wall charger. For circuit description and parts list, see the simple charger page. Since wall chargers....
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Continuous monitoring of the mains voltage is required in many applications such as manual voltage stabilisers and motor pumps. An analogue voltmeter, though cheap, has many disadvantages as it has moving parts and is sensitive to vibrations. The solidstate....
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The State Jal Boards supply water for limited duration in a day. Time of water supply is decided by the management and the public does not know the same. In such a situation, this water alarm circuit will save the people from long wait as it will inform them....
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Today, most telephone equipment use a DTMF receiver IC. One common DTMF receiver IC is the Motorola MT8870 that is widely used in electronic communications circuits. The MT8870 is an 18-pin IC. It is used in telephones and a variety of other applications.....
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The schematic diagram shows an audio stage with a common-collector circuit. This does not damp the tuned circuit, but instead actually increases its response. This yields good sensitivity and selectivity. Due to the low supply voltage, the subsequent audio....
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This motor starter protects single-phase motors against voltage fluctuations and overloading. Its salient feature is a soft on/off electronic switch for easy operation. The transformer steps down the AC voltage from 230V to 15V. Diodes D1 and D2 rectify the....
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Quiz-type game shows are increasingly becoming popular on television these days. In such games, fastest finger first indicators (FFFIs) are used to test the player`s reaction time. The player`s designated number is displayed with an audio alarm when the....
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Wanting to use two white LEDs, the second device must be wired across the Emitter of the transistor and negative ground with its own limiting resistor wired in series, like R15 and D3 in the circuit diagram. If common red, yellow or green LEDs are required,....
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At the heart of this heat-sensitive switch is IC LM35 (IC1), which is a linear temperature sensor and linear temperature-to-voltage converter circuit. The converter provides accurately linear and directly proportional output signal in millivolts over the....
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The circuit shows one way of obtaining a voltage of 90V from a 1. 5V battery supply. The LT1073 switching regulator from Linear Technology ( operates in boost mode and can work with an input voltage as low as 1. 0 V. The switching transistor, which is hidden....
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The above pictured schematic diagram is just a standard constant current model with a added current limiter, consisting of Q1, R1, and R4. The moment too much current is flowing biases Q1 and drops the output voltage. The output voltage is: 1. 2 x....
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The circuit as shown in the figure employs 14 bi-colour (red and green) LEDs having three terminals each. Different dancing colour patterns are produced using this circuit since each LED can produce three different colours. The middle terminal (pin 2) of the....
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Those wanting private listening to their music program should add this Headphone Amplifier to the Modular Preamplifier chain. The circuit was kept as simple as possible compatibly with a High Quality performance. This goal was achieved by using two NE5532....
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Here is a simple non-contact AC power monitor for home appliances and laboratory equipment that should remain continuously switched-on. A fuse failure or power breakdown in the equipment going unnoticed may cause irreparable loss. The monitor sounds an alarm....
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This circuit is very useful while checking/operating counters, stepping relays, etc. It avoids the procedure of setting a switch for the required number of pulses. By pressing appropriate switches S1 to S9, one can get 1 to 9 negative-going clock pulses,....
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Using this circuit, you can change the speed of the fan from your couch or bed. Infrared receiver module TSOP1738 is used to receive the infrared signal transmitted by remote control. The circuit is powered by regulated 9V. The AC mains is stepped down by....
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We`ve all had occasion to be annoyed at inconsiderate dog owners whose animals relieve themselves on the private property of others. This problem can hardly be solved in a lasting manner using verbal (or even physical) means, so recourse to an electronic....
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This ultra-simple remote control extender is ideal for use with a hidden video recorder. The recorder is a Panasonic NV-SD200 and is used as part of a camera surveillance system. A PICAXE-08-based circuit is used to detect events and control the recorder. It....
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Nearly always when a remote control doesn`t work, the underlying problem is elementary: the unit does not emit light. The cause may be dry solder joints, defective LEDs etc. , but also a flat battery (perhaps due to stuck key). The human eye is unable to....
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Such jobs as jewel cutting and polishing require the workers to switch on/off two electrical appliances one after another repeatedly for two different services on the same workpiece. This is cumbersome as they need to fully concentrate on delicate handwork....