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ne555 datasheet

ne555 datasheet

Description


These devices are monolithic timing circuits capable of producing accurate time delays or oscillation.

In the time delaymode of operation, the timed interval is controlled by a single external resistor and capacit

or network. In the astable mode of operation, the frequency andduty cy clemay beindependently

controlled with two external resistors and asingle external capacitor.
 
 
Features
                                                                                                              Pin Configuration
 
Timing from Micro seconds to Hours                    
 
Astable or Monostable Operation
 
Adjustable Duty Cycle
 
TTL - Compatible Output Can Sink or Source Up to200mA
 
Temperature Stability of0.005%per oC
 
Direct Replacement for Signetics NE555Timer
 
 
                                                                                               Internal Block Digram

  Applications
                                                                        
. Precision timing
. Pulse generation
. Sequential timing
. Timedelay generation
. Pulse width modulation
. Pulse position modulation
. Missing pulse detector
 
 
 
 
 
 
download ne555 datasheet pdf file

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BATTERY CHARGER SCHEMATIC

BATTERY CHARGER SCHEMATIC

High Efficiency Battery Charger using Power components ... Battery Charger. The complete schematic for a 12 V/15 V battery ... Figure 3. High-efficiency battery charger schematic. page 3 of 4. Efficiency Estimation ...

DOWNLOAD
http://cdn.vicorpower.com/documents/design_articles/pb_battery-charger.pdf

High Efficiency Battery Charger using Power componentS ... Battery Charger. The complete schematic for a 12V/15V battery ... Figure 3. High-efficiency battery charger schematic. page 3 of 4. Efficiency Estimation ...

DOWNLOAD
http://www.ur-group.co.uk/vicor/pdfs/power/pb_battery-charger.pdf

Smart Battery Charger Evaluation Kit User's Manual The Smart Battery Charger Evaluation Board schematic diagram and other related drawings are ... When a battery is connected to the charger and the Z8 enables ...
DOWNLOAD
http://www.zilog.com/docs/z8/battery_charger/ch3_hw.pdf

Battery Charging (PDF) 3A Battery Charger with Logic-level Controls ... Figure 7 shows the schematic of a battery charger that was designed to recharge the Li ...

DOWNLOAD
http://www.national.com/appinfo/power/files/f7.pdf

Battery charger using the ST6-REALIZER inflection points can be implemented with this battery charger ST6 board. HARDWARE SCHEMATICS ... 2/14. Figure 1 : Simple Battery Charger Circuit Schematic ...

DOWNLOAD
http://www.st.com/stonline/products/literature/an/2527.pdf

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How to Use a FM Transmitter to Listen to Internet Radio

How to Use a FM Transmitter to Listen to Internet Radio

Gone are the good old days of Internet radio when you had to stay chained to your desktop PC to enjoy the music. The FM transmitter takes any audio coming from a computer and transmits it to a FM radio, allowing you to use your FM radios as speakers.

Now you can wander through the house listening to your favorite songs.

Decide which type of FM radio transmitter is best for you. There are several types on the market that differ in size, transmission distance, power supply method, number of FM transmitter frequencies, portability and price.


Purchase a FM transmitter. You can buy them online or at a local electronics retailer.Such as http://www.papatek.com/Cell%2DPhone%2DAccessories

Connect the FM transmitter to its power source and then to your PC. Read the manufacturer's instructions for your model. Depending on the type of FM transmitter you buy, it may be powered by batteries, computer USB port or AC power. Most models come with the necessary connection cables. A FM transmitter USB simply plugs into a USB port of any computer
 http://www.papatek.com/Cell-Phone-Accessories/Blue-LED-F ...


Locate an available FM frequency on the dial of your FM radio. The manufacturer's instructions will list the frequencies that are available with the FM transmitter. It is not uncommon that you will probably need to try more than one of the listed frequencies before you find one that works.

Listen and enjoy your favorite Internet radio music or program with the freedom to move around. http://www.papatek.com/Cell-Phone-Accessories/FM-Transmitter-Hands-free-Car-Kit-For-Blackberry-Phone.html

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Broadband Colpitts VCO for TV Tuner

Broadband Colpitts VCO for TV Tuner


The high performance of modern set-top DBS TV tuners require broadband voltage control oscillator (VCO) designs at a competitive cost. To realize these goals, design engineers are challenged to create high performance, low-cost VCOs.

The traditional design of Colpitts oscillator is used for many VCO applications. Designing a broadband Colpitts oscillator with coverage from 1–2 GHz requires the selection and interaction of an appropriate varactor diode for its resonator. This design describes a broadband Colpitts VCO that incorporates the SMV1265-011 varactor diode.
 
 


Broadband Colpitts Variable Controll Oscillator 1-2 GHz Schematic





Broadband Colpitts Variable Controll Oscillator 1-2 GHz PCB Layout




This varactor diode was specifically developed at Alpha for this application. The VCO design, based on Libra Series IV simulation, shows good correlation between measured and simulated performance. This application note includes a board layout and materials list.


More info: A Colpitts VCO for Wideband (0.95–2.15 GHz) Set-Top TV Tuner Applications
 
http://www.ziddu.com/download/9053779/1-2ghzvco.pdf.html

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VGA to TV Converter Circuit

VGA to TV Converter Circuit

This converter circuit basically takes VGA signals and converts it to RGB + composite sync signal which can be fed to TV via SCART connector. VGA card picture components RED, GREEN and BLUE are already at the correct voltage level (0.7Vpp) and has correct impedance (75 ohm) for direct connection to correspondign inputs in the TV.


VGA to TV Converter Ciruit



VGA to TV Converter Printed Circuit Board (PCB)





For combining separate horizonal and vertical sync signal from VGA card to one composite sync signal needs a sync signal conversion which is feed to TV video in pin in SCART connector. The tv converter circuit has also sends correct level signal to the TV RGB input enabling control pin in the SCART connector (pin 16).




The circuit is simply based on one TTL chip with four XOR ports, two resistors and two capacitors. TTL chip was logical choise because VGA sync signals are TTL level signals.



The sync signal combiner has a system to adjust to different sync polarities so that it always makes correct composite sync signals. VGA card uses different sync signal polarities to tell the monitor which resolution is used. This circuit adjusts to sync signal polarity changes in less than 200 milliseconds, which is faster than setting time of a normal VGA monitor in the display mode change. The tv converter circuit needs well regulates +5V (+/-5%) power supply and takes about 120 mA current.



VGA to TV converter parts list are as follow:



Main circuit

U1 74LS86 (74HC86 or 74HCT86 can also be used)

C1 22 microfarads 16V electrolytic capacitor

C2 use 47 uF 16V electrolytic for more reliable operation (22 uF listed schematic can cause problems in some cases)

R1,R2 2.2 kohm, 1/4 W

R3,R4,R5 2.2 kohm, 1/4 W

R6,R7,R9 47 ohm, 1/2 W

R8 120 ohm, 1/2 W

T1,T2 BC547B (2N2222 should also work but note the different pinout)

P1 15 pin SUB-D connector (DE-15)



Output connector

21 pin EURO/SCART connector

Wiring:

Red, Green, Blue and Composite Sync lines should be wired using 75 ohm coaxial cable for best picture quality, but can be replaced with normal shielded wire.



Power supply components

7805 regulator chip

100 uF electrolytic 25V

10 uF electrolytic 16V

100 nF polyester or ceramic condensator

Wall adapter which outputs 8-18V DC and 150 mA or more current

Connector for connecting wall adaptor to circuit





Source: http://www.tkk.fi/Misc/Electronics/circuits/vga2tv/circuit.html

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Simple High efficiency Inverter Circuits

Simple High efficiency Inverter Circuits

Description


1. Field of the InventionThis invention relates generally to the field of electrical energy conversion systems and more particularly to push-pull inverter circuits utilizing a solid state active element oscillator of the multivibrator type to convert an input DC voltageto a high frequency AC output voltage.2. Description of the Prior ArtPush-pull inverter circuits are generally recognized as the most efficient type for converting DC voltage into an AC output voltage. Such circuits typically include a source of DC potential, an output transformer, and a pair of switchingtransistors connected to control the flow of current through the output transformer for thereby producing an AC voltage output across the transformer. Efficient conversion of the DC voltage into the AC output voltage requires that the conduction of theswitching transistors be precisely controlled. Such precise control can serve to minimize undesirable energy losses within the circuit itself. Some of the causes of such energy losses have been recognized and are generally regarded as inherent in suchcircuits, or in the components making up such circuits. Some of these losses are:1. Common-mode conduction which occurs when both of the switching transistors conduct simultaneously. This loss is usually related to the inherent and generally unavoidable delay associated with the turn-off action of the conducting transistor,coupled with the fact that there generally is no corresponding delay associated with the turning on of the other transistor.2. Turn-off transition loss which is due to the power dissipation that occurs within each transistor during its turn-off transition. To minimize this loss, it is necessary to operate each transistor near its maximum switching speed capability. This in turn requires that the charge carriers stored at the transistor base-emitter junction be evacuated as rapidly as possible.It is also more important to prevent the collector voltage from rising significantly be

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AM FM Antenna Booster


This antenna booster circuit can be used to amplify the weak signal received by the antenna. Antenna for AM/FM is usually not tuned for the optimal dimension of 1/4 wavelength, since we prefer small portable size. This untuned antenna has very low gain, so the antenna booster circuit here is very helpful in getting better signal reception. Here is the schematic diagram of the circuit:

Use around 470uH coil for L1 if you use for AM frequency (700kHz-1.5MHz) and use around 20uH for SW or FM receiver. For short wave performance, using this antenna booster, you’ll get a strong signal as we get from a 20-30 feet antenna, with only a standard 18″ telescopic antenna and this booster circuit. The power supply should be bypassed by a 47nF capacitor to ground, at a point that should be chosen as close as possible to L1.

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UHF Antenna Booster

UHF Antenna Booster

UHF antenna booster can be used for better reception, especially when you’re far from TV station / relay transmitter. This UHF antenna booster works in 400-850 MHz range. Here is the circuit diagram of the UHF antenna booster:


The circuit use only one transistor, but it gives you 10 to 15 dB amplification, enough for many situation. The most important part is that the transistor circuitry should be shielded from the input circuitry, as shown in the schematic diagram by the dashed line. This ircuit is powered via the signal cable, since the antenna booster circuit must be wired as close as possible to the antenna. This is very important since the amplifier should amplify the signal acquired by the antenna, not the noise picked by the cable from the antenna to the circuit. The antenna and the booster circuit can be installed above your house’s roof. Long 75 ohm coaxial cable can be drawn from the this booster circuit output to the power supply unit close to TV set.


Just insert a 50-10o uH inductor or RF choke between the output cable and the power supply. Tap the output signal from the output cable using a small 100pF ceramic capacitor to block the DC voltage from the power supply. Adjust P1 to get the best reception, and this should set the working current consumption to around 5-15 mA.

source :http://freecircuitdiagram.com/2009/05/30/uhf-antenna-booster/

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10 Watt Car Audio Amplifier

10 Watt Car Audio Amplifier

TDA2003 is audio amplifier integrated circuit chip in 10 Watt class. All you need is just adding few passive components and your amplifier will be ready. You can even amplify ultrasonic range if you wish to abuse its usage, just to convince you that this chip is more than enough to handle any range of audio signal. Although many manufacturer produce this TDA2003 chip, in general, this various chip from various manufacturer normally comply with these following features: Short circuit protection between all pins, High current output ( up to 3 A), Built-in Over temperature protection, and Low harmonic and crossover distortion.


source :http://freecircuitdiagram.com/2008/08/04/10-watt-car-audio-amplifier/

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Car Stereo Booster with LM2896

Car Stereo Booster with LM2896

This car stereo booster uses an LM2896 IC which has two integrated amplifiers. It can be powered with voltages up to 15 volts. The power output is 2.5 watts per channel with an 8 Ω load and supply voltage of 12 volts. Using the bridge tehnique in the circuit gives a power output of 9 watts. The car audio booster can be powered up from 3 up to 15 volts.

Car stereo booster circuit diagram

The load impedance that can be connected at its output can be either 4 Ω or 8 Ω. The supply voltage and the load impedance influence the output power level. This amplifier circuit is designed as a booster for auto radio/cassette players. The current consumption by maximum power output and a 4 Ω load is 1 ampere.













more info and source : http://mycaramplifiers.com/car-stereo-booster-with-lm2896-395.html

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200 watts amplifier TDA2030


TDA 2030 is produced by SGS Ates and is a complete audio amplifier. AB class of the final amplifier cand deliver up to 14W on 4 ohm at a +-14V power supply.


Connecting two TDA2030 thru cheap power transistors we can create a amplifier wich can deliver a higher power. With the components value from the schematic the total amplifier gain is 32 dB. The speaker can be 2 ohm instead of 4 ohm if we use the TIP transistors. With a proper designed power supply this audio amplifier can output 200W.
 
Active components:


IC1, Ic2 TDA 2030

T1, T3 = BD 250, TIP 36

T2,T4 = BD 249, TIP 35

D1 … D4 = 1N4001
source:http://mycaramplifiers.com/200-watts-amplifier-tda2030-8.html

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amplificador operacional

LM 741 .- Amplificador Operacional


National



Semiconductor


LM741/LM741A/LM741C/LM741E Operational Ampiifier


General Description


The LM741 series are general purpose operational amplifi-


ers which feature improved performance over industry stan-


dards like the LM709. They are direct, plug-in replacements


for the 709C, LM201, MC1439 and 748 in most applications.


The amplifiers offer many features which make their appli-


cation nearly foolproof: overload protection on the input and
 
output, no latch-up when the common mode range is ex-



ceeded, as well as freedom from oscillations.


The LM741C/LM741E are identical to the LM741/LM741A


except that the LM741C/LM741E have their performance


guaranteed over a 0°C to f 70°C temperature range, in-


stead of - 55°C to ! 125°C
 
download  datasheet LM 741 .- Amplificador Operacional National Semiconductor

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Two Transistors Wireless Microphone FM Transmitter Circuit Schematic Diagram

Two Transistors Wireless Microphone FM Transmitter Circuit Schematic Diagram

Please be warned if operating this circuit might violate the regulation of your country, because this FM transmitter circuit radiate strong radio frequency to the environment. This wireless microphone is very sensitive, pick up every sound in the 20m radius, and transmit the radio signal up to 2 kilometers in open air. Here is the schematic diagram of the circuit:














The first transistor (Q1) is the pre-amplifier for the microphone, and you can ommit this circuit if you don’t want to transmit the sound picked up by the mic, for example you can can connect your mp3 player directly to C1. The core of this FM transmitter circuit is Q2, a modified Collpits oscillator that the frequency is determined by L1, C4, C6, and the transistor’s internal base-emitter capacitance. The antenna use 1/16 wave length to compromize between the efficiency and the size. If you want the microphone to be less sensitive, you can replace the R1 by a higher resistor, try 10k or 22k, and this might overcome the feedback problem if you use this wireless microphone FM transmitter for a public address system.

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Metal Detector Circuit Schematic using Beat Frequency Oscillator (BFO)

Metal Detector Circuit Schematic using Beat Frequency Oscillator (BFO)

The simplest method of detecting metal is by beat frequency oscillator. The circuit basically consists of two balanced oscillator. One acts as the detector element, the other provides the reference signal. This oscillator frequency reference is set to fix value, whilst the detector oscillator varies depending on the metal presence. The reference oscillator can be constructed using various circuit topology: inductor-capacitor (LC), resistor-capacitor (RC), or even a crystal (quartz) oscillator. While the reference oscillator can be implemented using various circuit topology, the detector oscillator always use inductor-capacitor topology, because the mechanism will be using the magnetic induction property of the detected object, and the inductor component of the detector oscillator will be the detecting probe.













With the absence of a metal near the detector probe (the inductor component of the detector oscillator), the detector oscillator is tuned to have same frequency as the reference oscillator. The output of the detector oscillator and the reference oscillator output is mixed using hetero-dyne mixer circuit, producing a beat frequency output of zero Hz, or a very low frequency if both oscillator is slightly unbalanced. In the presence of a metal near the detector probe, the detector oscillator will shift it’s frequency, and the mixer output will produce a tone with frequency equal to the difference of the reference and the detector frequency.




The figure below shows one of the simple metal detector circuit.You can see the reference circuit is a simple RC circuit, and its frequency is determined by R1-P2-C1. The detector oscillator is an LC oscillator with the frequency is determined by the L1-C2-C3 values.



The NAND gates use CMOS 4011 chip, a low power component that is suitable for this battery-operated circuit. You can see that this chip is supplied by a 5V voltage coming from an LM7805L regulator. You might wonder what the purpose of this regulation is, since the power supply come from a 9V battery and the CMOS gates can handle the voltage of 3-15 Volt. The main purpose of the regulator is to keep a constant voltage source for the reference oscillator frequency stability, since the frequency is affected by the power supply voltage variation as the battery voltage drops in the long time of usage.



Here the complete parts list:



Parts list:

U1: CD4011

U2: LM389

U3: 78L05

R1: 2.2k 5%

P2: 4.7k lin.

R3: 330k 5%

R4: 270k 5%

R5: 1k 5%

C1: 390pF (NPO)

C2,C3,C4: 10nF

C5: 10uF 16v electrolytic

C6,C8: 220 uF 16v electrolytic

C7: 100uf 16v electrolytic

C9: 100nF ceramic

P1: 4.7k log

L1: 22cm in diameter with 14 turns AWG 26

K1: SPDT toggle switch

J1= Headphone jack 1/4 or 1/8 inch

Other parts: 9v battery connector, speaker or headphones



To tune the circuit, plug a headphone at the output, and remove any metal around the inductor L1. Set the volume control P1 around at center. Set the reference oscillator tuner P2 at the maximum or minimum position, you should hear no sound since the frequency should be in ultrasonic range. Turn slowly P2 until you hear a very high audio frequency, continue turning the pot until the frequency is decreasing and stop turning when the note is just disappeared (the frequency is decreased down below 20 Hz). After this, you can test the circuit by placing a metal near the inductor L1 and now the output will give an audible frequency as the detection alert. [Circuit schematic diagram source: hobby-hour.com]

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One transistor FM receiver

One transistor FM receiver

In this exciting project, not only will you have a very unique one transistor FM recevier, but also be in-store for making home-made air-core coils and a home-made fixed capacitor. And even more than that, when you finish ‘your’ project, your journey has just started. With your now-working FM receiver, you can start experimenting with other wonderful things.There are 12 component count on this project. One transistor FM receiver


at http://www.somerset.net/arm/reprints/radio_shack_special/rss.html

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Schematic diagram for the One Transistor FM Radio with Improved Audio Gain

Schematic diagram for the One Transistor FM Radio with Improved Audio Gain




One Transistor FM Radio with improved audio gain.




Some wiring notes:




Unless you have experience with super-regenerative radios, I highly recommend using the FAR Circuits printed circuit board.



Connect the two sections of the variable capacitor (C3) in series to linearize the tuning somewhat. That is, use the connections on either end of C3 and don't use the middle lead.
L2, the RF choke should not be near a ground. The same is true for L1. Capacitance to ground will disturb the feedback.

The gain is just enough to drive an earphone. If you live too far away from radio stations, you might have trouble hearing one. There is no option here for an external antenna (that would require and extra transistor).

You can drive a speaker if you add an external audio amplifier.

If you want a little more audio gain, or you cannot locate a TL431CLP chip, you can use some other audio amplifier in the circuit where pins 1 and 2 of D1 normally connect. You can use an LM386 or a TDA7052 audio amplifier. Quasar DIY project kit #3027 is a complete TDA7052 audio amplifier kit and it works fine in this application.

source : http://www.somerset.net/arm/fm_only_one_transistor_radio.html

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A Novel Fermi Level Controlled High Voltage Transistor Preventing

A Novel Fermi Level Controlled High Voltage Transistor Preventing

Fermi-level Controlled HVT(FCHVT) is a new

transistor which improves hump by turning off the FETp.

Controlling doping concentrations of gate edge of

MOSFET makes the differences of work function of poly-

gate shift the Fermi-level between FETp and FETi, and

humps are improved by increase of Vth of FETp. We

explored to control gate doping concentration with ion

implantation on MOSFET as illustrated in Fig. 2
 

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Automatic cooler fan for amplifiers

Automatic cooler fan for amplifiers

Description.
The schematic of an automatic cooler fan for audio amplifiers is given here. The circuit automatically switch ON the cooler fan whenever the temperature of the heat sink exceeds a preset level. This circuit will save a lot of energy because the cooler fan will be OFF when the amplifier is running on low volume. At low volume less heat will be dissipated and it will not trigger the cooler fan ON.

The temperature is sensed using an NTC (negative temperature coefficient) thermistor R2. Junction of thermistor r2 and resistor R1 is connected to the inverting input (pin3) of IC1 which is wired as a comparator. The non-inverting input (pin2) is given with a reference voltage using the preset R3. As temperature increases the resistance of NTC thermistor will drop and so do the voltage across it. When the voltage at the inverting input becomes less than that of the reference voltage (set for a particular threshold temperature) the output of the comparator goes high and switches the transistor Q1 ON. This will activate the relay and the cooler fan will be switched ON. When the temperature decreases the reverse happens. LED D2 will glow when the fan is ON. Diode D1 is a freewheeling diode.

Notes.
The circuit can be assembled on a Vero board.
Use 12V DC for powering the circuit.
The circuit can be calibrated by adjusting the preset R3.
K1 can be a 12V, 200 ohm, SPST relay.
LM311 must be mounted on a holder.

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Cell inspired electronics


Cell  inspired electronics

A single cell in the human body is approximately 10 000 times more energy-efficient than any nanoscale digital transistor, the fundamental building block of electronic chips. In one second, a cell performs about 10 million energy-consuming chemical reactions, which altogether require about one picowatt (one millionth millionth of a watt) of power.
Rahul Sarpeshkar of the Massachusetts Institute of Technology (MIT) is now applying architectural principles from these ultra-energy-efficient cells to the design of low-power, highly parallel, hybrid analogue-digital electronic circuits. Such circuits could one day be used to create ultra-fast supercomputers that predict complex cell responses to drugs. They may also help researchers to design synthetic genetic circuits in cells.

In his new book, Ultra Low Power Bioelectronics (Cambridge University Press, 2010), Sarpeshkar outlines the deep underlying similarities between chemical reactions that occur in a cell and the flow of current through an analogue electronic circuit. He discusses how biological cells perform reliable computation with unreliable components and noise (which refers to random variations in signals — whether electronic or genetic). Circuits built with similar design principles in the future can be made robust to electronic noise and unreliable electronic components while remaining highly energy efficient. Promising applications include image processors in cellphones or brain implants for the blind.

"Circuits are a language for representing and trying to understand almost anything, whether it be networks in biology or cars," says Sarpeshkar, an associate professor of electrical engineering and computer science. "There's a unified way of looking at the biological world through circuits that is very powerful."

Circuit designers already know hundreds of strategies to run analogue circuits at low power, amplify signals, and reduce noise, which have helped them design low-power electronics such as mobile phones, MP3 players and laptop computers.

"Here's a field that has devoted 50 years to studying the design of complex systems," says Sarpeshkar, referring to electrical engineering. "We can now start to think of biology in the same way." He hopes that physicists, engineers, biologists and biological engineers will work together to pioneer this new field, which he has dubbed "cytomorphic" (cell-inspired or cell-transforming) electronics.

To read more, go to
http://web.mit.edu/newsoffice/2010/cytomorphic-0225.html
 



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STK4132II - Schematic audio amplifier - power amplifier 2x20w

STK4132II - Schematic audio amplifier - power amplifier 2x20w
STK4132II  - Schematic audio amplifier.STK4132II  power audio amplifier schematic

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stk392 datasheet - schematic circuit diagram -

                                                                                              internal equlvalant ciruit

The STK392-020 is a hybrid IC for video projector
convergence correction. Since this IC integrates three
output amplifier circuits in a single package, the six
convergence correction output circuits, i.e., the vertical
and horizontal directions for each CRT of the RGB can be
formed from only two ICs.

Applications
Video projectors (both standard and high definition)                                            test circuit
                                                                                             
Features
•Three output amplifier circuits integrated in a single
22-pin package
•High absolute maximum supply voltage
(VCC max = ±44 V)
•Low thermal resistance (θj-c = 2.1 °C/W)
•High thermal stability (TC max = 125°C)
•Isolated early stage and output stage power supplies
•Output stage power supply switching supports high
efficiency designs.

•The input system, power supply system and output
system pins are isolated in the pin arrangement, thus
reducing the influence of the pattern layout on the
characteristics and easing design.
•Since constant current circuits are used in the pre-driver
stage, operation is stable with respect to the power
supply switching.
•The Sanyo convergence correction circuit product
lineup (the STK392-000 series) handles a wide range of
end-product classes. Therefore, the same PCB can be
used for end products from popularly-priced units to
top-of-the-line models.
Package Dimensions

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Low voltage DC motor speed control circuit using TDA7274

 Low voltage DC motor speed control circuit using TDA7274

Description.
Here is the circuit diagram of a low voltage /low power DC motor speed controller based on the IC TDA 7274 from ST Microelectronics. The IC TDA 7274 is a monolithic integrated DC motor speed controller intended for low voltage/ low power applications. Built in internal voltage reference voltage, wide input voltage range (1.8 t0 6V), high linearity, 700mA output current, excellent temperature stability etc make this IC well suitable for almost all low power DC motor speed control applications.
The motor to be controlled is connected between pin3 (Vs) and pin4 (output) of the IC. Resistor network comprising of R1, R2, and R3 is the section that deals with the speed control. Control pin (pin8) of the IC is connected to the junction of R2 and R3 and the speed of the motor varies linearly according to the position of POT R3. Capacitor C1 rectifies the fluctuations in motor speed and capacitor C2 cancels the motor spikes.

Notes.
The circuit can be assembled on a Perf board.
Power supply Vs can be anything between 1.8V to 6V and it must be selected according to the rating s of the motor.
Maximum output current capacity of this circuit is 700mA.
TDA7274 must be mounted on a holder.
POT R3 can be used to vary the motor speed

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Audio line driver

Audio line driver
Description.

This is the circuit diagram of a two channel audio line driver using the high performance dual opamp IC TSH22 from ST Microelectronics. The 25 MHz bandwidth, low distortion and high output current of the IC makes it possible to drive medium impedance loads at a high level of modulation.

Here both of the opamps inside the IC are wired as non inverting amplifiers with 3X gain, one for each channel. Input line 1 is connected to the non inverting input of IC1a and input line 2 is connected to the non inverting input of IC1b. The non inverting inputs of the opamps IC1a and IC1b are pulled to a slight positive voltage using the R1 and R9 respectively. The resistance R4 and R2 are used to make a phantom ground at half the supply voltage.


Notes.
Assemble the circuit on a good quality PCB.
The circuit can be powered from 12V DC.
At 12V supply, a 600 ohm impedance line can be driven at +10dBm with a distortion less than 0.05% at 1kHz.
Gain of line 1 can be set using the equation, Gain1 = (R5+R6)/R6.
Gain of line 2 can be set using the equation, Gain2 = (R7+R8)/R8.
The load at the output must be at least 100 ohms in order to avoid stability issues.

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