Top Circuits Page 274
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A 12 Volt high current 20 Amp power supply. The output voltage is variable from 12. 2 Volt to 14. 4V so can be set for any device requiring voltage and current in that range. This PSU uses an LM723 as the regulator, 4 parallel connected outboard pass....
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This circuit allows you to set a limit on the maximum output current available from your PSU. It`s very useful when you power-up a project for the first time - or carry out a soak-test. By setting an upper limit on the current available from your PSU - you....
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The schematic is shown above, and two switches S1 and S2 are used to control the outputs. The main work is done by U2 a CMOS4017 decade counter divider IC. At switch on, C1 is quickly charged by R4 and a brief reset pulse is applied to to the reset pins of....
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This circuit uses a synthesized sound chip from Holtek, the HT-2811. This reproduces the sound of a "ding-dong" chiming doorbell. Additionally, the circuit includes a CMOS 4026 counter display driver IC to count your visitors. The Holtek HT-2811 is available....
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This circuit is designed to operate an electrical door-release mechanism - but it will have other applications. Enter the four-digit code of your choice - and the relay will energize for the period of time set by C4 & R4. Use the relay contacts to power the....
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This is a universal version of the Four-Digit Alarm Keypad. I`ve modified the design of the output section - to free up the relay contacts. This allows the circuit to operate as a general-purpose switch. I used a SPCO/SPDT relay - but you can use a....
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This is a simplified version of the Universal Keypad-Operated Switch. I have modified the design to reduce the complexity of the circuit - and the number of components required. As a result - the code is somewhat less secure. However, there should be lots of....
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The purpose of this prototype unit does away with the need for an oscillator. It offers a mains-derived and fully variable 50 hz AC volts down to millivolts for comparison and to check accuracy, of two or more parallel connected multimeters. Sometimes older....
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In the first circuit, above the BC548 is wired as a colpitts oscillator, the frequency tuned by insertion of a crystal. A good crystal will create high frequency oscillations, the output at the collector is rectified by the germanium OA91 diode and a....
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Built around a single 8038 waveform generator IC, this circuit produces sine, square or triangle waves from 20Hz to 200kHz in four switched ranges. There are both high and low level outputs which may be adjusted with the level control. This project makes a....
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This RF probe can be used at High Frequency (HF) or Ultra High Frequency (UHF) on both 50 and 75 ohm coaxial cables. In addition the RF voltage can be measured under load or no-load conditions which allows the circuit to double as an RF Watt meter. The RF....
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In this circuit a standard op-amp is wired as an astable multivibrator. The output is non-symmetrical but has the advantage that the timing is controlled by only 1 resistor and capacitor, in this case, the 100k variable resistor, U2 and 100u capacitor C1.....
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This index is arranged alphabetically on each word (except prepositions). For example, the "Frost Alarm" will be indexed under "A" and also "F". To quickly find a circuit use the top index or try your browsers search function. In Firefox, Konqueror, Opera....
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This circuit provides an FM modulated signal with an output power of around 500mW. The input Mic preamp is built around a couple of 2N3904 transistors, audio gain limited by the 5k preset. The oscillator is a colpitts stage, frequency of oscillation governed....
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Designed around the popular ZN414 IC this receiver covers the medium wave band band from approximately 550 to 1600 KHz with the values shown. The coil and tuning capacitor may be taken from an old MW radio to save time. The ZN414 IC, has now been replaced by....
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An AM voice transmitter with variable tuning. The antenna circuit is also tuned and transmits via a long wire antenna. Please Note. It is illegal to transmit on the AM wavebands in most countries, as such this circuit is shown for educational purposes only.....
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The circuit uses two 2N3819 FET`s in cascode configuration. The lower FET operates in common source mode, while the upper FET, operates in common gate, realising full high frequency gain. The bottom FET is tunable allowing a peak for a particular station.....
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My site contains a few low power transmitters of one type or another, but until now no receiver. This circuit can be used to "sweep" an area or room and will indicate if a surveillance device is operative. The problem in making a suitable detector is to get....
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The RF engineer sometimes has to look for an instrument that will check a low frequency quartz crystal unit reliably and rapidly. This is a difficult piece of equipment to find and the engineer often has to consult an electronic circuits handbook for the....
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This small transmitter uses a hartley type oscillator. Normally the capacitor in the tank circuit would connect at the base of the transistor, but at VHF the base emitter capacitance of the transistor acts as a short circuit, so in effect, it still is. The....
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The power output of many transmitter circuits are very low because no power amplifier stages are incorporated. The transmitter circuit described here has an extra RF power amplifier stage, after the oscillator stage, to raise the power output to 200-250....
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Contrary to what some radio experimenters think, a bipolar regenerative design can be made to work efficiently. The major concern is the low input impedance of the detector-amplifier bipolar stage. Nevertheless, it can be easily compensated with positive....
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Sensitivity and selectivity are issues that will invariably concern a short wave listener when he wishes to purchase a new receiver. Commercially available communications equipment will undoubtedly fulfill his expectations, but we are talking here of highly....
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The problem with amplifying weak radio signals is that you also amplify the noise. What you can receive depends on how much background noise is present, whether it be man made interference or static. In this design the RF signal is first met by a resistive....
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This is a small battery operated Tracking transmitter which broadcasts a repeating radio signal which can be detected by a directional antenna. The transmitter broadcasts an isotropic (radiates in all directions) signal on the FM band. An ordinary FM radio....
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This is an Analogue TV Transmitter. Sound modulation is type FM with a 5. 5MHz carrier and video transmission is PAL. Frequency is adjustable via C5 and tunes 54 to 216Mhz with components shown. This is suitable for countries using TV systems B and G. Please....
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This page was created in response to all the email I receive, on how to read a schematic. Learning to read a schematic diagram, is similar to map reading. You need to know which wires connect to which component and where each wire starts and finishes. With a....
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How to construct a circuit on veroboard by reading the schematic. If you`re an experienced constructor, then you will just look at the schematic and start assembly. Experience tells you where to place components and use veroboard space to its best advantage.....
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Frequency-to-voltage converters form part of a wide variety of instrumentation circuits. They also find use in radio as FM demodulators. One interesting configuration for this application is the Diode Charge Pump circuit (DCP), which also doubles as an AM....
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The usual procedure for the production of sustained oscillations in tuned L-C networks is to overcome circuit losses through the use of designed-in positive feedback or regeneration. Then, during the circuits on-transient oscillations will build up triggered....
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To measure the input impedance of an unknown circuit first set the signal genaerator to a current source of magnitude 1 amp. You also need a shunt resistor of 100 Meg. This setup is useful for measuring amplifiers, filter and oscillator circuits. Use the....
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These two circuits are multi-range timers offering periods of up to 24 hours and beyond. They can be used as repeating timers - or as single-shot timers. Both circuits are essentially the same. The main difference between them is their behaviour in....
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This circuit places a maximum limit on the current available from the output terminals. It does this by limiting the maximum current that can flow through Q1. Because the output terminals are in series with Q1 - limiting the Q1 current also limits the output....
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Although this Power Supply was designed for the Modular Burglar Alarm - it has other applications. It provides an output of 12-volts - at a current of up to 1-amp. In the event of a mains failure - the back-up battery takes over immediately. And when mains....
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This circuit features automatic exit and entry delays - an optional instant alarm zone - an optional intermittent siren output - and an automatic reset. By adding external relays you can immobilize the vehicle and flash the lights. For automatic operation -....
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When a keypad switch is pressed - this circuit will reproduce its value in Binary Coded Decimal from. I`ve used a 12-key pad. But it may be expanded to 16 keys - to provide Hexadecimal to BCD conversion. The circuit is constructed in two parts. There`s a....
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The Cmos 4001 has four - independent - two-input NOR gates. The four gates are divided into two pairs. Gates 1 & 2 are wired together to form a type of latching circuit. When the alarm is triggered - they will latch - and sound the buzzer. Gates 3 & 4 are....
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This is a 1-amp variable-voltage PSU. It adjusts from about 3v to 24v: and has the added feature that you can limit the maximum output current. This is invaluable when (for example) you power-up a project for the first time or soak-test a piece of equipment.....
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This is a simplified version of the Universal Keypad-Operated Switch. I have modified the design to reduce the complexity of the circuit - and the number of components required. As a result - the code is somewhat less secure. However, there should be lots of....
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The prototype of Keypad Switch No. 2 was built using only the Stripboard Layout as a guide. So - if you have faithfully reproduced that layout - you will have a working circuit. Once you`re satisfied that your layout is correct - and you have made a careful....
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This is a single zone alarm - with automatic exit, entry and siren cut-off timers. It will accommodate all the usual types of normally-closed input devices - such as magnetic-reed contacts - foil tape - PIRs etc. But it`s easy to add a normally-open trigger.....
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This is a simple - easy to build - multi-purpose alarm. Build it yourself using stripboard or veroboard and a few cheap off-the-shelf components. Fit it to a door, window, shed, garage, cupboard etc. It`ll alert you to intruders. Fit it to a shop-door - and....
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This circuit is designed to operate an electrical door-release mechanism - but it will have other applications. Enter the four-digit code of your choice - and the relay will energize for the period of time set by C4 & R4. Use the relay contacts to power the....
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Before fitting this or any other engine cut-out to your vehicle - carefully consider both the safety implications of its possible failure - and the legal consequences of installing a device that could cause an accident. If you decide to proceed - you will....
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This is a battery powered IR Link which may be used in more than one room. The standby current is extremely low - so battery life is excellent. And by shutting down in the presence of extraneous IR radiation - it copes with the problem of excessive output....
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Pressing a single key on the keypad - will energize the relay. Entering a four-digit code of your choice - will de-energize the relay. The circuit was designed to control the Modular Burglar Alarm System - but it will have other applications. If you require....
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This circuit is designed to be used with the Universal Keypad Operated Switch. A few genuine mistakes - made during code entry - will not activate the device. But repeated attempts to find the correct code by trial and error - will cause the keypad to....
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The Basic Alarm Circuit has an automatic Exit/Entry Zone - an Instant Alarm Zone that will accept both normally-closed and normally-open triggering devices - and an "Always On" 24-hour Personal Attack/Tamper Zone. By using the Expansion Modules - you can add....
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When one of the normally-open switches is closed - two things happen. Firstly - the negative side of the relay coil is connected to ground through D1. This causes the relay to energize. And the relay in turn sounds the siren. = Secondly - the emitter-base....
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This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can....
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This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can....
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When one of the switches is closed - the base of Q1 is connected to ground through D1 & R2. This switches Q1 on - and it in turn switches Q2 on. Q2 connects the positive side of the relay coil to the supply line. The relay energizes - and the siren sounds. =....
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This is a selection of small self-contained alarm circuits. The main features of each alarm are described on the circuit diagram itself. They all have a very low standby current. So they are ideal for battery operation. Each pair of circuits will print out....
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This alarm is designed to sound its Siren only once. That is - when the alarm is activated - the Siren will sound for a preset length of time. Then it will switch off and remain off. The alarm will not re-activate. The basic alarm has a single zone with....
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This is a universal four-digit keypad-operated switch - with a difference. Instead of entering the security code one number at a time - the four keypad buttons must be pressed simultaneously. In other words - the four numbers must be entered in parallel. The....
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This circuit has an adjustable output timer that will re-trigger at regular intervals. The output period can be anything from a fraction of a second to half-an-hour or more - and it can be made to recur at regular intervals of anything from seconds to days....
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This circuit is based on a simple asymmetric oscillator. The length of time the relay remains energized - and the length of time it remains de-energized - are set independently. With the component values shown in the diagram - both periods are adjustable....
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This circuit is very similar to Repeating Timer No. 2. However - the addition of the light dependent resistor means that the operation of this timer can be limited to the daylight hours. R7 lets you set the level of light at which the timer will stop. The....
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This timer is based on a simple Monostable Circuit. The length of time the relay remains energized - the ON period - is controlled by the values of R3 & C2. And the length of time the relay remains de-energized - the OFF period - is controlled by the values....
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The Cmos 4060 IC has two built-in inverters - at pins 9, 10 and 11. They must be wired together to form an oscillator - the output of which is at Pin 9. While the oscillator is running - Pin 9 is switching continuously from high to low and vice-versa. It`s....
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This is a simple SCR based burglar alarm circuit. Its features include automatic Exit and Entry delays - together with a timed Bell cut-off and Reset. It`s designed to be used with the usual types of normally-closed input devices such as - magnetic-reed....
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You can add as many extra zones as you like to the SCR Burglar Alarm System. The first circuit is designed to be used with the usual types of normally-closed input devices such as - magnetic-reed contacts - micro switches - foil tape - and PIRs. The second....
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This is a simple single-zone burglar alarm. The basic design includes automatic Exit and Entry delays. It doesn`t include a siren cut-off timer. But with A Small Modification - you can add one to the circuit. The alarm will accept the usual types of....
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This is an enhanced version of the simple Garage/Shed Alarm. The Entry and Exit delays have been increased to about 30-seconds - and I`ve added a timed Siren cut-off and automatic Reset. I`ve also replaced the LED with an entry Buzzer. These enhancements....
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This circuit uses a Cmos 4017 decade counter to create a sequence of four separate events. The number of events in the sequence may be increased to nine or ten. And the length of each event is controlled independently. D13 causes the sequence to repeat....
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This circuit uses a Cmos 4017. The 4017 is a decade counter. The count starts at zero. And it advances by one - each time pin 14 is taken high. When the count reaches nine - it goes back to zero - and starts all over again. = As the count progresses - each....
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This simple circuit will energize and de-energize a relay at the push of a button. Any type of momentary action push-to-make switch can be used. Pushing the button once - will energize the relay. And pushing it a second time - will de-energize the relay.....
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This circuit uses a Cmos 4017. The 4017 is a decade counter. The count starts at zero. And it advances by one - each time pin 14 is taken high. When the count reaches nine - it goes back to zero - and starts all over again. = As the count progresses - each....
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This versatile circuit provides a selection of different switching modes. It can be used as two entirely separate toggle switches - with each push button successively energizing and de-energizing its own relay. Or the two switches can be interlinked with....
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You can add as many extra zones as you like to the Transistor Burglar Alarm System. The first circuit is designed to be used with the usual types of normally-closed input devices such as - magnetic-reed contacts - micro switches - foil tape - and PIRs. The....
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You can use a Cmos 4001 or a Cmos 4011 in this circuit. They have four - two-input - gates. In each case - the two inputs are joined together. So the gates are being used as simple inverters. = This means that when the two inputs are high - the output will....
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This is a two-zone alarm - with automatic exit, entry and siren cut-off timers. It can be triggered by the usual types of normally-closed input devices - such as magnetic reed contacts - foil tape - PIRs etc. I`ve used a 12-volt supply in the diagram - but....
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The key you`ve connected to "E" is used to energize the relay. And the four keys you`ve connected to A, B, C & D - are used to de-energize it. All the other keys on the keypad are connected to "F". = When "E" is pressed - current from the "Com" terminal....
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This circuit uses two signal generators to simulate an Amplitude Modulated RF carrier wave. The output can be used to simulate the response of LC and tank circuits. Two signal generators are used in this circuit, one representing a high frequency (200kHz) RF....
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This is a zine dedicated to electronics circuit diagrams, diy (do it yourself) electronics projects, electrical electronics data sheets, and micro controller projects for hobbyist, students, consultants and product designers...
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This interface design comes a long way. This is in fact the first microcontroller design I`ve ever started. Somehow it kept going with me during past few years. I probably drew the first lines of the schematics diagram of the first prototype in early 1998.....
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The inputs of the 74LS153 chip were mixed, which caused the address block decoding to fail. By now, I know of two Commodore 64 (mine and Pekka Pessi`s) where this expansion has been built, and of four Commodore 128s (of which two expanded by me, and the....
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A block diagram of the Commodore 64 internal power supply (how the +12V, +9V and TOD clock signals are generated from the 9V AC input). Taken from the SAMS C64 Troubleshooting Guide. Commodore 64 schematic diagram, scanned with 360 DPI, 2 colours. This seems....
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VIC-20CR rev. D (NTSC, new design). Assy number 251027-01. The PAL model has a crystal frequency of 4433618 Hz, and there is an extra 56pF capacitor on the solder side of the board, soldered parallel to R5...
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This circuit came out of some work I did for the two antenna analysers which are described elsewhere on this site. Those instruments both include an RF signal generator. This is used as the signal source to drive the impedance bridge and detectors used to....
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Accessories built so far include a linear power supply, a switchmode power supply, a tuning aid, and a headset. An antenna tuner and SWR meter will be described later. In order to operate the new transceiver, I needed a power supply. I began by building a....
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As equipment becomes increasingly more compact, designers are often obliged to follow suit by reducing the size of displays. At some point, the usefulness of the display can become compromised. I, for one, dislike having to peer intently at tiny displays in....
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This compact RF oscillator covers the entire 0. 4 - 30 MHz range in a single sweep of the dial and has a terminated 50 ohm output of more than 300mV across the entire HF band. Most signal generators use a series of ranges to cover the HF band. This....
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A 80m (3. 5 - 3. 9 MHz) SSB transceiver using a Collins 455 kHz mechanical filter in the IF chain. Such designs need some good front-end receiver selectivity in the form of at least a couple of selective tuned circuits. I`m also planning to build a simple....
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Results are shown on an analog VSWR meter. The design was originally published in `Break-In`, New Zealand`s amateur radio magazine in Sept/Oct 2005, and is republished here with the permission of the editor. Note: `Break-In` is a term used in amateur radio....
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A couple of cheap CMOS ICs are used to digitally generate audio sinewaves across a wide range in this compact battery-powered test instrument. The oscillator features both unbalanced and balanced outputs. I use signal generators of one sort or another all....
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This instrument measures complex impedance over the 1. 6 - 33 MHz HF spectrum. It also calculates and displays the VSWR of the impedance referenced to 50 ohms. The most common application of the meter is as an antenna analyser. The design was published in....
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Two cheap CMOS ICs and a few transistors was all that was required to rebuild my elderly TTL automatic morse keyer into a low current lightweight battery powered iambic morse keyer. Sometime over the past year or two, my elderly Accu-Keyer gave up the ghost....
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After I built my KN-Q7 kitset 40m QRP single sideband (SSB) transceiver, described elsewhere on this site, I went on to build a matching low power "Z-match" antenna tuner and a sensitive SWR meter. For some reason, I found I needed three hands to tune this....
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This manual is for use by authorised Sinclair dealers. engineers and representatives as a guide to rectifying faults on the Sinclair ZX Printer. Repair/renewal procedures are limited to those which are specific to this printer; standard procedures for the....
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This is a general purpose remote control project with using programmable PIC microcontrollers. Schematics are shown for using infrared (RF) or radio (RF) media. If you are not familiar with microcontroller programming, you can use fixed encoder and decoder....