PDF Drive is your search engine for PDF files. As of today we have 78,, eBooks for you to download for free. No annoying ads, no download limits, enjoy . Michael Tooley BA. Formerly Vice Principal. Brooklands College of Further and Higher Education. Electronic Circuits: Fundamentals and. Applications. After reading this book, the reader should be able to analyze and construct electronic circuits (amplifiers, filters, oscillators, converters, etc.) with real active circuit elements: Operational amplifier; Transconductance amplifier; Transimpedance amplifier; Current conveyor.

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A basic understanding of electronic circuits is important even if the designer does electronic circuits will allow the mechanical engineer to evaluate whether or. Section 1. Analog Circuit Design. Second Edition .. Syscomp Electronic Design Limited Bob Dobkin, Vice President, Engineering, Maxim Integrated Circuits. The information contained within this Basic Electronics Tutorials guide is provided "as-is" and free of and electronic circuits and soldering irons. Thank you and.

This is 10mA minimum and 2 amp maximum. Reaching the current limit will reduce the output voltage to zero. Voltage and current regulation equations can be found at this page. I have had several requests for a power supply project without using a power supply. This can save the expense of downloading a transformer, but presents potentially lethal voltages at the output terminals. Under no circumstances should a beginner attempt to build such a project.

Please also read the Disclaimer on this site. Important Notice: Electric Shock Hazard. In the UK,the neutral wire is connected to earth at the power station. If you touch the "Live" wire, then depending on how well earthed you are, you form a conductive path between Live and Neutral. Whilst the output of this circuit sits innocently at 12V with respect to wrt the other terminal, it is also 12V above earth potential.

Should a component fail then either terminal will become a potential shock hazard. Below is a project by Ron J, please heed the caution above and Ron's design notes. If you are not experienced in dealing with it, then leave this project alone. Although Mains equipment can itself consume a lot of current, the circuits we build to control it, usually only require a few milliamps. Yet the low voltage power supply is frequently the largest part of the construction and a sizeable portion of the cost.

This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn't generate very much heat. The circuit draws about 30ma AC. The values given are only a guide. There should be more than enough power available for timers, light operated switches, temperature controllers etc, provided that you use an optical isolator as your circuit's output device.

C1 should be of the 'suppressor type'; made to be connected directly across the incoming Mains Supply. They are generally covered with the logos of several different Safety Standards Authorities.

If you need more current, use a larger value capacitor; or put two in parallel; but be careful of what you are doing to the Watts. The bridge rectifier can be any of the small 'Round', 'In-line', or 'DIL' types; or you could use four separate diodes. If you want to, you can replace R2 and ZD3 with a 78 Series regulator.

The full sized ones will work; but if space is tight, there are some small ma versions available in TO 92 type cases. They look like a BC It is also worth noting that many small circuits will work with an unregulated supply. You can, of course, alter any or all of the Zenner diodes in order to produce a different output voltage. As for the mains voltage, the suggestion regarding the v version is just that, a suggestion.

I haven't built it, so be prepared to experiment a little. RON J Email: This circuit will generate a smaller DC output voltage from a larger DC input voltage.

It is quick and simple to make and by changing the value of the zener diode, the circuit can be universally adapted to provide other output voltages. The output voltage is equal to the zener diode voltage less 0. With the 10V zener diode as shown in the diagram the output voltage is about 9. The supply voltage used must always be at least a few volts higher than the zener voltage.

Output Regulation Versus Input Voltage The above graph shows how the output is affected by input voltage variations. This was produced with a load current of mA and using a 10 volt rated zener diode. Note that the circuit falls sharply out of regulation when the input voltage falls to The output voltage changes by 8.

Power dissipation is the product of the transistors emitter current and collector-emitter voltage. With this circuit the maximum power dissipation of the BD or maximum collector current cannot be exceeded, otherwise the transistor will be destroyed. With a 12 Volt supply and a 9 Volt, mA load the dissipation is as follows. Using a 10 volt zener the output voltage will be about 9. If higher load currents are required then the following circuit may be used.

Output dissipation is calculated in the same way, the BD has a maximum power dissipation of 15 watts and collector current of 3 amps.

The output voltage is approximately 1. As Ron suggests, controlling the output voltage from a regulator can be made variable in three ways: Using a fixed reference zener diode to increase the output by the value of the zener 2. A variable resistor for variable output, note that a voltage less than the nominal regulator is not possible 3. Matthew Hewson I constructed this voltage regulator to power my two way mobile radio from the car cigarette lighter circuit.

It has many other uses and the voltage can easily be adjusted by the use of a potentiometer. The voltage regulator is an LMT, and should accept up to about 14 volts without problems. It can handle up to 1 amp, but you WILL need a heatsink on the voltage regulator. The components are: The over voltage LED uses a zener diode to switch on the LED at a certain preset voltage, this can be varied depending on the voltage of the zener diode, I used a 6. If you plan to vary the voltage for the different items you power, don't bother adding this feature.

You can even add a relay to switch off the power if the over voltage LED turns on, but bear in mind it will have to work from the voltage of the zener diode right up to the input voltage. I couldn't add a relay because I couldn't find any that operated from 6. Anyway, the schematic is shown above, the over voltage and power LED are not included in them because it is assumed that anybody who makes this will understand how to use a zener diode: This is what the final product should look like inside: This is an outside view of the finished voltage regulator: Here is what my voltage regulator is intended to power: In the event of electrical supply line failure the battery takes over, with no spikes on the regulated supply.

This circuit can be adapted for other regulated and unregulated voltages by using different regulators and batteries.

For a 15 Volt regulated supply use two 12 Volt batteries in series and a regulator. There is a lot of flexibility in this circuit. TR1 has a primary matched to the local electrical supply which is Volts in the UK. The secondary winding should be rated at least 12 Volts at 2 amp, but can be higher, for example 15 Volts. FS1 is a slow blow type and protects against short circuits on the output, or indeed a faulty cell in a rechargeable battery.

The circuit below simulates a working circuit with mains power applied: Resistor R1 and D1 are the charging path for battery B1. D1 and D3 prevent LED1 being illuminated under power fail conditions. The battery is designed to be trickle charged, charging current defined as: An electrical power outage is simulated below: Note that in all cases the 5 Volt regulated supply is maintained constantly, whilst the unregulated supply will vary a few volts.

Standby Capacity The ability to maintain the regulated supply with no electrical supply depends on the load taken from the UPS and also the Ampere hour capacity of the battery. Adam Email: The original circuit may be viewed here.

It is a voltage regulator that allows a 6v portable supply to be derived from the 12v car battery. You can add a 6. If you could find a relay that would operate from 6. Such a relay would be quite difficult to find, so I designed this, it is a simple two transistor circuit which will switch off the output should the voltage raise above 6.

Components are as follows: This circuit is intended to be used with the voltage regulator posted by Matthew Hewson, my overvolatge add-on circuit is shown with the original below: Also, if you want to increase the power output of the voltage regulator circuit above 1 Amp then connect several LM's in parallel, be sure to make sure that transistor T2 on this circuit is of a high enough rating if you do this. If you have any problems with this circuit, you can email me at: Please read the disclaimer on this site before making any transmitter circuit.

It is illegal to operate a radio transmitter without a license in most countries. This ircuit is deliberately limited in power output but will provide amplitude modulation AM of voice over the medium wave band. The circuit is in two halfs, an audio amplifier and an RF oscillator. The oscillator is built around Q1 and associated components. These components can be used from an old MW radio, if available.

Q1 needs regenerative feedback to oscillate and this is achieved by connecting the base and collector of Q1 to opposite ends of the tank circuit.

The 1nF capacitor C7, couples signals from the base to the top of L1, and C2, pF ensures that the oscillation is passed from collector, to the emitter, and via the internal base emitter resistance of the transistor, back to the base again. Resistor R2 has an important role in this circuit. It ensures that the oscillation will not be shunted to ground via the very low internal emitter resistance, re of Q1, and also increases the input impedance so that the modulation signal will not be shunted.

Oscillation frequency is adjusted with VC1. Q2 is wired as a common emitter amplifier, C5 decoupling the emitter resistor and realising full gain of this stage. The microphone is an electret condenser mic and the amount of AM modulation is adjusted with the 4. An antenna is not needed, but 30cm of wire may be used at the collector to increase transmitter range.

AM Receiver 2. MW Preamplifier by David Sayles 3. SW Receiver using the ZN 7. FM Transmitter by David Sayles 9. Simple Field Strength Meter Surveillance Transmitter Detector This is a compact three transistor, regenerative receiver with fixed feedback. It is similar in principle to the ZN radio IC which is now no longer available. The design is simple and sensitivity and selectivity of the receiver are good.

All general purpose transistors should work in this circuit, I used three BCC transistors in my prototype. The tuned circuit is designed for medium wave. I used a ferrite rod and tuning capacitor from an old radio which tuned from approximately - kHz.

Q1 and Q2 form a compund transistor pair featuring high gain and very high input impedance. This is necessary so as not to unduly load the tank circuit. The k resistor provides regenerative feedback,between Q2 output and the tank circuit input and its value affects the overall performance of the whole circuit. Too much feedback and the circuit will become unstable producing a "howling sound". Insufficient feedback and the receiver becomes "deaf". If there is a lack of sensitivity, then try increasing R1 to around k.

R1 could also be replaced by a fixed resisor say 33k and a preset resistor of k. This will give adjustment of sensitivity and selectivity of the receiver. Transistor Q3 has a dual purpose; it performs demodulation of the RF carrier whilst at the same time, amplifying the audio signal. Audio level varies on the strength of the received station but I had typically mV.

This will directly drive high impedance headphones or can be fed into a suitable amplifier. All connections should be short, a veroboard or tagstrip layout are suitable. The tuning capacitor has fixed and moving plates. The moving plates should be connected to the "cold" end of the tank circuit, this is the base of Q1, and the fixed plates to the "hot end" of the coil, the juction of R1 and C1.

If connections on the capacitor are reversed, then moving your hand near the capacitor will cause unwanted stability and oscillation. Finally here are some voltagee checks from my breadboard prototype. This should help in determining a working circuit: The tuning voltage is variable from 1 to 12 volts and is designed to cover the medium waveband from about Khz to Khz. Once again, this is a project designed by David Sayles.

The input can be from a longwire or a loop antenna. Click here for a picture of David's MW loop. Click here to view a finished picture of this project.

Courtesy of David Dayles. For Longwave the coil needs to be changed. Use one from an old MW radio to save time. It is easily overloaded and the operating voltage is critical to achieve good results.

The BC acts as a voltage follower, the four 1N diodes providing a stable 2. With the 10k pot , which acts as a selectivity control, and the b-e voltage drop of the BC, the operating voltage for the ZN is variable from 0 to 1. If you live in an area that is permeated with strong radio signals, then the voltage will need to be decreased.

I found optimum performance with a supply of around 1. The audio amplifier is built around an inverting op-amp. The voltage gain of the complete audio amplifier is around The audio output of the complete receiver is really quite good and free from distortion.

I may provide some sound samples later. Click here to see a picture of my prototype. I used a small wooden enclosure and the complete tuning assembley from an old radio. The original data sheet for the ZN states that the maximum working frequency is around 4 MHz. That may be true, but SW broadcasts are so powerful that this receiver will work well with signals up to around 6 or 7 mhz. The 10k resistor controls the operating voltage for the ic which is critical for good performance.

The tuned circuit consists of a variable capacitor and fixed air spaced coil. For the inductor, I wound 10 turns of wire on an empty tube of around 1. The turns were spaced so that the overall length was around 3 inches. The variable capacitor tuned 0 - pF but there is plenty of scope for experiment here.

One final point, you will need an external antenna to receive broadcasts. I have an outside wire that is about 7 meters long and this was quite effective.

The antenna can be connected at either end of the coil or via a series capacitor value between 10pF and pF. Take care with transmitter circuits. It is illegal in most countries to operate radio transmitters without a license. Although only low power this circuit may be tuned to operate over the range MHz with a range of 20 or 30 metres.

I have used a pair of BC transistors in this circuit. Although not strictly RF transistors, they still give good results. It is a two terminal ECM, but ordinary dynamic mic inserts can also be used, simply omit the front 10k resistor.

The coil L1 was again from Maplin, part no. UF68Y and consists of 7 turns on a quarter inch plastic former with a tuning slug. The tuning slug is adjusted to tune the transmitter.

Actual range on my prototype tuned from 70MHz to around MHz.

Electronics - Circuits and Systems, Fourth Edition

The aerial is a few inches of wire. Although RF circuits are best constructed on a PCB, you can get away with veroboard, keep all leads short, and break tracks at appropriate points. One final point, don't hold the circuit in your hand and try to speak. Body capacitance is equivalent to a pF capacitor shunted to earth, damping all oscillations. I have had some first hand experience of this problem.

The frequency of oscillation can be found from the theory section,and an example now appears in the Circuit Analysis section. 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 coil is four turns of 18swg wire wound around a quarter inch former. The aerial tap is about one and a half turns from the supply end. Audio sensitivity is very good when used with an ECM type microphone insert.

David's email: This circuit measures radio field strength by converting the signal to DC and amplifying it. The inductor L1 is 4 to 6 turns of 20swg wire air spaced wound on a quarter inch former or similar. Alternatively an inductor of value 0. Sensitivity is not as good as I would have liked, but a small 9 volt battery transmitter will deflect the meters needle from a distance of up to two feet from the FSM. Higher power transmitters give higher signal strength readings and of course from much further away.

The meter used was a signal meter with FSD of uA. Lower FSD meters will offer greater sensitivity. The FET used in this circuit is a general purpose 2N A small telescopic whip antenna is used for signal pickup. The RF signal, whether modulated or just a plain carrier, is rectified and converted to DC by the diode,capacitor and 3.

This small DC voltage just enough to upset the bias of the circuit and hence cause a deflection of the meter. This Field Strength Meter is simple and also quite sensitive. It uses an ordinary digital voltmeter to measure signal strength. The VM should be set to the lowest dc volts range for maximum sensitivity.

This is normally mV DC for most meters. I have tried this at VHF and was quite pleased with the results. L1 was 7 turns on a quarter inch former with ferrite slug. This covered the UK FM band. A digital multimeter, as opposed to an analogue signal meter has several advantages in this circuit.

This does not shunt the tank circuit unduly. Second, as opposed to an analogue meter, very small differences in signal strength can be observed more easily on the digital meter.

This circuit provides an FM modulated signal with an output power of around mW. The input Mic preamp is built around a couple of 2N transistors, audio gain limited by the 5k preset. The oscillator is a colpitts stage, frequency of oscillation governed by the tank circuit made from two 5pF capacitors and the inductor.

Frequency is around Mhz with values shown. The oscillator output is fed into the 3. The output stage operates as a class D amplifier , no direct bias is applied but the RF signal developed across the 3. The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage.

Paul K. Sherby Belleville, Michigan.

USA Website: R8 is at least 0. L1 is 0. Q1 is configured as a Clapp oscillator. Frequency modulation results from the audio voltage changing the transistor's base-emitter capacitance.

It has a gain of around 10dB and is suitable for boosting weak TV signals. The circuit is shown below: The tuned circuit comprising the 15nH inductor and 2.

The 2. The approximate frequency response is shown below. Output was measured into a 1k source and the frequency generator has a 75ohm impedance. This ensures a low Q and therefore broad tuning. High frequency work requires special construction techniques to avoid instability unwanted oscillations caused by feedback from output to input.

Veroboard is not suitable for this project as the capacitance between tracks is around 0. A better approach is to use tag-strip or a PCB. The circuitry should be enclosed in a metal case and a screen made between input and output. As the transistor is used in common base mode,its low input impedance is a good match for ohm coax cable, whilst at the same time providing full voltage gain to the upper frequency limit of the device. The 15nH inductor load, having almost a short circuit impedance at DC, has an impedance of 56ohms at MHz.

This inductance and 2. Note however that the voltage gain will be reduced under load, when the circuit is connected to the input of a TV set or a very long piece of coaxial cable for example.

Hence the simulated Tina plot. All ATL-3 loop windings are centre tapped and balanced w. Magnetic noise fields,e. Tuned winding antennas always have a potential 6dB greater signal sensitivity, and provide a better signal to noise ratio than equally sized broadband designs; thus a much larger broadband loop area becomes necessary to better the performance of the standard 40 inch frame loop with d.

Note that the switched ATL-3 amplifier circuit will work just as well from kHz to 3MHz with a seven turn 40" MW box loop, by simply extending a ground connection to a centre tap at the middle of the winding.

ATL-3 loop windings are in the shape of a five 65cms. Winding turns are 2mm. Loop corner formers can be made from sections of unclad 0. Do try combining your loop signal with the signal from an outdoor wire or active whip antenna. Whatever your loop gain, it can be doubled in one direction in line with the loop, with deep nulling in the opposite direction The controls do not need to be complicated, see the circuit drawings below.

The Medium Wave Circle can be found by clicking here. 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 a detector is to get its sensitivity just right, Too much sensitivity and it will respond to radio broadcasts, too little, and nothing will be heard.

This project has few components, can be made on veroboard and powered from a 9 volt battery for portability. My prototype shown below worked OK on a Eurobreadboard.

Fast Analytical Techniques for Electrical & Electronic Circuits

Circuit operation is simple. The inductor is a moulded RF coil, value of 0. See my links page for component suppliers. The coil has a very high Q factor of about and is untuned or broadband. With a test oscillator this circuit responded to frequencies from 70 MHz to MHz, most of the FM bugs are designed to work in the commercial receiver range of 87 - MHz. The RF signal picked up the coil, and incidentally this unit will respond to AM or FM modulation or just a plain carrier wave, is rectified by the OA91 diode.

Meters with an FSD of 50 or uA may be used for higher sensitivity. In use the preset is adjusted for a zero reading on the meter. The detector is then carried around a room, a small battery transmitter will deflect the meter from a few feet away. Graham Maynard Text: This new loop antenna by Graham Maynard is his best design yet and I am proud to be the first to present his work. It uses one, six foot square, six turn loop, and is aperiodic in nature, covering the frequency range 50KHz - KHz.

The loop is of a size that can be mounted inconspicuously against a garden fence away from household interferences. This new '6x6' design uses the centre tapped loop winding as an input phase splitter.

This ensures low distortion push-pull operation. The amplifier also has a low impedance shunt input which maximises gain. These aspects give it a better signal to noise ratio than with a single ended or high impedance amplifier. The amplifier provides a useful gain of 42 - 54dB over its frequency range, see the Bode Plot below.

Please note, that the Bode plot is derived for the amplifier circuit ONLY, it is not possible to simulate the characteristics of a six foot square loop. The first MPSA18 transistor on each loop operates in common emitter, the collector being directly coupled to a double emitter follower pair. The network of resistors and capacitors around the base of each MPSA18 transistor tailors the amplifier response to the specified limits. The double emitter follower pair evenly distributes the Class A heat dissipation, and direct feedback in the bias chain, counters temperature drift effects.

The output from each amplifier half is fed via a 2: There is equal but opposite current flow and therefore maximum linearity. The output is isolated, which minimizes earth loop noise injection, either via receiver earth leakage or loop amplifier psu earth leakage. To power the amplifier a separate twin flex may be used speaker wire , though it is possible to use a mains PSU via the coax itself.

The overall phase response is reasonably flat throughout any band, thus any cardioid or other developed reception patterns can remain directionally stable over a decent frequency range, which might be useful for trans-oceanic MW reception. It is intended that the centre-tap be made at the mid point along the bottom six foot antenna span, and this may be grounded with an earth stake.

Sometimes reception on some bands can be made quieter by grounding this centre tap. You should to try the '6x6' with and without the ground on your favourite band. To ensure stability, the component layout should follow the above circuit layout, with all signal ground connections being kept as short and thick as possible in the centre of the pcb. This is of course a sensitive DXing antenna, thus it might be overloaded if used too close to a local broadcast transmitter.

You can null powerful signals by setting the loop up at right angles to their source, i.

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Please let Graham know if you construct this antenna, he is interested in hearing of everyone's results. Rob van der Weijden Email: Andy Collinson Description: A compact 2 transistor transmitter for use at VHF frequencies.

The audio input is applied at the points LF in on the diagram. P1 works as gain control. After amplification this audio signal now modulates the transmitter built around T2. Frequency is tunable using the trimmer CT and L1 is made using 3 turns of 1mm copper wire wound on a 5mm slug.

The modulated signal passes via C6 to the antenna. A DC power supply in the range 3 to 16 volts is required. Patrick Cambre Email: A radio frequency amplifier to boost SW reception. Frequency range approximately 5 to 20 MHz. 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 attenuator, this is necessary as strong signals could otherwise overload your receiver.

The transformer T1 is would on a 1 inch diameter ferrite loop. The primary antenna side is 2 turns of 22 swg wire. The secondary is 4 turns of 22 swg wire. The 4 turns are spaced to occupy roughly half the coils circumference. The approximate inductance of the secondary is 20uH. To cover 5 to 20 Mhz a capacitor tuning from around 3pF to pF is required. A standard capacitor of or pF full mesh can be used by including a series capacitor, C2 in the above Capacitors.

Capacitors in series behave the same as resistors in parallel. The smallest capacitance is just less than the smallest capacitor in series and highest value also less than the highest capacitance.

With a pF capacitor for C2 and a pF variable capacitor that tunes down to 5pF the effective capacitance tunes pF to about 4. This is roughly correct and not critical as the gain of the FET will amplify frequencies outside the tuned circuit range.

The 2N FET operates in common source. The drain circuit includes a 2.

Textbook of Engineering Drawing

As the Q factor of these coils are high, a series resistor R3 is introduced to flatten the response. Current drain is around 3mA from a 9 Volt battery. As with any RF circuit, the circuit is sensitive to noise and interference. A metal or aluminum box would be a good choice for this project.

However, on my trusty breadboard, this circuit preformed well, and weak signals were boosted well. Parts List: Tone Controls 4. Stereo Line Driver 5. TDA 8 Watt amplifier 6. Hi-Fi Pramplifier by Graham Maynard 9. Peak Reading Audio Level Meter Computer Microphone by Lazar Pancic Voice-Over Circuit Quadraphonic Amplifier Soft switching Amplifier with Tone Controls This was one of the earliest circuits that I ever designed and built, in Spring At that time I had only an analogue meter and a calculator to work with.

Although far from perfect, this amplifier does have a wide frequency response, low distortion, and is capable of driving an 8 ohm speaker to output levels of around 5 watts with slightly higher distortion.

Any power supply in the range 12 to 18 Volts DC may be used. Adjustment here, is a trade-off between low distortion and low quiescent current. Typically, under quiescent conditions, standby current may be 15 mA rising to mA with a 50 mV input signal. A simulated frequency response is shown below: The circuit is DC biased so that the emitters of the BD and BD are at approximately half supply voltage, to allow for a maximum output voltage swing.

All four transistors are direct coupled which ensures: The BCC and 2N operate in common emitter. This alone will provide a very high open loop gain. Overall gain is provided by the ratio of the 22k and 1k resistor. Both transistors are low noise types. In the original circuit, I used BCC which is an ultra low noise device.

These transistors are now hard to find but BCC are a good replacement. The circuit is very device tolerant and will set its quiescent point at roughly half the supply voltage at the emitter of the last transistor. The electret condenser microphone ECM contains a very sensitive microphone element and an internal FET preamp, a power supply in the range 2 to 10 volts DC is therefore necessary. The 1k resistor limits the current to the mic.

The output impedance is very low and well suited to driving cables over distances up to 50 meters. Screened cable therefore is not necessary. The noise response of the amplifier measured across the 10k load is shown below.

Please note that this plot was made with the mic insert replaced by a signal generator. This preamplifier has excellent dynamic range and can cope with anything from a whisper to a loud shout, however care should be taken to make sure that the auxiliary equipment i.

Based on the classic Baxendall tone control circuit, this provides a maximum cut and boost of around 10dB at 10K and 50Hz.

As the controls are passive, the last transistor provides a slight boost. The output is designed to feed an amplifier with input impedance of 10k to k. This preamplifier has a low output impedance, and is designed to drive long cables, allowing you to listen to a remote music source without having to download expensive screened cables.

The very low output impedance of around 16 ohms at 1KHz, makes it possible to use ordinary bell wire,loudspeaker or alarm cable for connection. The preamplifier must be placed near the remote music source, for example a CD player. The cable is then run to a remote location where you want to listen. The output of this preamp has a gain of slightly less than one, so an external amplifier must be used to drive loudspeakers.

Although the TDA can deliver 20 watts of output power, I deliberately reduced the output power to about 8 watts to supply 10 watt speakers. Input sensitivity is mV. Higher input levels naturally will give greater output, but no distortion should be heard. The gain is set by the 47k and 1. The TDA IC is affordable and makes a good replacement amplifier for low to medium audio power systems. Incidentally, it is speaker efficiency that determines how "loud" your music is.

Advanced Electronic Circuits

The controls may also be adjusted for use as a band stop notch filter or band pass filter. The mixer circuit below has 3 line inputs and 3 mic inputs. The mic inputs are suitable for low impedance R dynamic microphones.

An ECM or condenser mic can also be used, but must have bias applied via a series resistor. As with any mixer circuit, a slight loss is always introduced. The final summing amplifier has a gain of 2 or 6dB to overcome this. The mic inputs are amplified about times or by 40dB, the total gain with the mixer is 46dB. The mic input is designed for microphones with outputs of about 2mV RMS at 1 meter. Most microphones meet this standard. Graham Maynard Email graham.

It has an exceptionally fast high frequency response, as demonstrated by applying an kHz squarewave to the input. All graphs were produced using Tina Pro. Application Notes: Using minimum component count; this simple circuit will indicate peak audio response on an analogue meter, similar to a tape recorders meter.

The circuit uses an opamp as a non inverting amplifier, but with one addition - a diode in the feedback loop. The circuit has a fast response time and slow decay time to indicate peak readings. The 1N diode provides half wave rectification of the input signal, the dc output being smoothed by the 22u capacitor. The discharge time is around a quarter of a second. Increase the 22uF cap for a longer discharge time, or omit altogether to make an instantaneous reading level meter.

This page is also available in French by clicking on the flag. In this doorphone circuit,an 8 ohm speaker is used both as a microphone and also an output device. The BCC stage amplifies in common base mode, giving good voltage gain , whilst providing a low impedance input to match the speaker. Self DC bias is used allowing for variations in transistor current gain.

An LM is used in non-inverting mode as a power amplifier to boost voltage gain and drive the 8 ohm speaker. The double pole double throw switch, reverses the loudspeaker positions, so that one is used to talk and the other to listen. Manually operating the switch from inside the house allows two way communication.

La polarisation d'individu est tenue compte a utiliser de petites variations de gain du dispositif. This circuit was submitted by Lazar Pancic from Yugoslavia. The sound card for a PC generally has a microphone input, speaker output and sometimes line inputs and outputs. The mic input is designed for dynamic microphones only in impedance range of to ohms. Lazar has adapted the sound card to use a common electret microphone using this circuit. He has made a composite amplifier using two transistors.

The BCB operates in common emitter to give a slight boost to the mic signal. This is followed by an emitter follower stage using the BCC. This is necessary as the mic and circuit and battery will be some distance from the sound card, the low output impedance of the circuit and screened cable ensuring a clean signal with minimum noise pickup.

Supply voltage may be anything from 6 to 30 Volts. Maximum boost 20dB is only realized with maximum supply voltage. In its simplest form, a voice-over unit is just a microphone and change-over switch feeding an amplifier, the output from the microphone having priority over the amplifiers audio signal when the "push-to-talk" switch is pressed.

The changeover switch is nothing more than a relay with a single changeover contact. For completion, an amplifier based on the LM is shown. Three wires are needed to connect the remote microphone unit to the amplifier and switching unit. With reference to the above schematic, the two BCC transistors are used to make a microphone preamplifier. The left hand BCC operates in common emitter mode, the right hand emitter follower.

The combination form a high gain, low output impedance amplifier, capable of driving a long audio cable. Screened cable is not required as the output impedance from the microphone pre-amp is very low, and will be immune to mains hum and background noise. The output of the pre-amp is via a uF capacitor and 1k resistor. The 1k resistor here plays an important role, eliminating the dc component of the audio output.

See also eliminating the DC "thump" also on this web site. A cable of three or more wires is wired to the remote amplifier. The amplifier shown here is based on the National Semiconductor LM The input signal is passed via the normally closed contact of a changeover relay, the 10k potentiometer being the volume control for the audio input source. The 10k preset at the normally open contact allows volume control of the voice input, note that this signal has by-passed the normal volume control.

At the remote end, when the push-to-talk switch is pressed, the relay will operate and the "voice" signal will be heard in the speaker. There will be no "thump" or "thud" on voice-over as direct current has been eliminated as already mentioned.

A suitable application for this circuit would be for use in a remote location such as a workshop or shed. This is a four channel amplifier ideally suited for use with quadraphonic equipment such as a Sound Blaster Live card.

There is no volume control,audio levels being directly controlled from the sound card itself. Construction is straight forward and is suitable for Verobaord. Used with small hifi speakers the volume was too loud for my room so I reduced R14 and R6 to 33k.

The input impedance is high, 1M and if very long input cables are present could pick up noise. This provides a DC path to ground and higher noise immunity. If instability does occur, then you will notice sound distortion and the LMN will become hot to touch. The back of a sound blaster live card has colour coded 3. The image below shows a close up of the rear of my Sound Blaster Live card.

As well as colour coding, each connector has an appropriate marking, for easy connectivity. The normal output connector is green and the rear speaker connector is black. Creative provide utilities and sound mixer for use with Windows.

Under Linux the utility Gamix can be used, which allows independent volume control for all channels. A 15 watt amplifier made using discrete components.

Sergio designed this circuit for his Electronics Level II course. This amplifier uses a dual 20 Volt power supply and delivers 15 watts RMS into an 8 ohm load. Q8 and Q9 provide a constant current through the bias chain to minimize distortion, the output stage formed by a discrete darlington pair Q2,Q4 and Q7,Q The last two transistors are power Transitors, specifically the 2N and MJ The 7.

The 1. You can use this circuit with any walkman or CD player since it is designed to take a standard mv RMS signal. Matthew Hewson Email: Hewson btinternet. This circuit uses two quad op-amps to form an eight LED audio level meter. The op-amp used in this particular circuit is the LM It is a popular IC and should be available from many parts stores. The 1K resistors in the circuit are essential so that the LED's turn on at different audio levels.

There is no reason why you can't change these resistors, although anything above 5K may cause some of the LED's to never switch on. Pretty much any op-amp will work as long as you look up the pinouts and make sure everything is properly connected. The 33K resistor on the schematic is to keep the signal input to the circuit at a low level. It is unlikely you will find a 33K resistor, so the closest you can get should do. The value of this resistor may need to be changed, so it is best you breadboard this circuit before actually constructing it on PCB.

The circuit in it's current form will accept line level inputs from sources such as the aux out on a Hi-Fi, all though could be easily modified to accept speaker inputs. The 50k pot can be used to vary the sensitivity of the circuit. Built around an LM, this amplifier includes tone controls and electronic "soft switching". The soft switching circuitry ensures power is built up gradually eliminating the dc thump. The soft switching is enabled by a BD transistor wired as a switch in emitter follower configuration.

The collector is wired to a permanent supply voltage, the 2H series inductor serves only to filter out power supply hum. This inductor is not too important and may be omitted if the DC supply is adequately smoothed. The control voltage is applied to the BD base terminal, the 10u capacitor and 10k resistor having a dual purpose: LED1 will light when the amplifier is on.

The control voltage should ideally be 0 volts when the amplifier is off and full supply voltage when on. The LM is shown driving two 8 ohm loupspeakers, the load is therefore 4 ohms.

Tone Controls: The input of this is amplifier is via a tone control based on the baxendall design. The first BCC serves as a buffer, offering a high input impedance. The output signal fed via a 10u capacitors reaches the tone control network.

This passive network of resistors and capacitors attenuates high and low frequencies. The bass control is centered on Hz and treble control 10kHz. See the bode plot below: Bode response of Tone Controls: The traces show maximum lift, maximum cut and the response with tone controls in the centre position. Audio levels can be monitored using a small panel meter with this circuit built from discrete components.

The circuit has a flat frequency response from about 20Hz to well over 50Khz. Input sensitivity is mV for a full scale deflection on a uA meter. The last stage is biased to operate at roughly half the supply voltage for maximum ac voltage swing.

Audio frequencies are passed through the 10u dc blocking capacitor and the full wave bridge rectifier converts the signal to a varying dc voltage. Note that the meter reading is instantaneous and will not provide a "peak" reading. A peak reading audio level meter is also available on this site click this link. The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius. A suitable bead type thermistor is found in the Maplin catalogue. The k pot allows this circuit to trigger over a wide range of temperatures.

A slight amount of hysteresis is provided by inclusion of the k resistor. This prevents relay chatter when temperature is near the switching threshold of this circuit. Frost Alarm or Cold Activated Switch 2. Electronic Keypad by Ron J 4. Light Detector Circuit by Mick Devine 5. Push Button Switch Debouncer 7. Remote Doorbell Indicator 8. Doorbell with Counter 9. Digital Combination Lock Electronic Night Light Sound Operated Switch Voltage Comparator Switch DC Motor Reversing Circuit This circuit will activate a relay when light falls to a preset level.

Light level can be adjusted with VR1 and the relay contacts may be used to operate an external light or buzzer. The light sensor used is the ORP12 photocell. In bright light the resistance of the ORP12 can be as low as 80 ohm and at 50lux darkness the resistance increases to over 1 Mohm. The 1M control should provide a wide range for light intensities, if not its value may be increased. Example 2. According to Example 2. A method for the determination of N s will be discussed in?

Section 2. In particular, we can write the voltage gain: N s V s 2. A method for the determination of N s will be discussed in Section 2. The simple proposition stated above provides a very quick way of determining zeros of a transfer function directly from the circuit diagram. Assume that the 25 2. It is quite clear from Eq. The interesting thing is that a I null in the response can be most easily studied on the circuit diagram itself. As it turns out, each factor n s corresponds to a condition in the transform circuit G which prevents the excitation from reaching the response.

We begin by assuming that the transform response v s is zero, or a null, for some s : s , where s is a zero of M I I Figure 2. This is shown in Fig.The output signal fed via a 10u capacitors reaches the tone control network. We can see in Fig.

When placing the probes the common probe must be the lowest placed probe, as the water level rises, it will first pass probe 1, then 2 and finally probe 6.

These aspects give it a better signal to noise ratio than with a single ended or high impedance amplifier. Resistor R1 and D1 are the charging path for battery B1.

JAYNA from St. Paul
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