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We have put here a collection of circuits, many audio related. While many published circuits are not the finest available solutions today, they represent great ideas. If you would like your circuit or link collection be published here, send e-mail with related material, we will format it and add to our collection. Thank you!     Publish my circuit
Electronics Tutorials -  Extensive resources for circuit design    http://www.williamson-labs.com
Technick.net - Tons of hardware info and more   http://www.technick.net
Electronics Tutorials - Extensive resources for circuit design, biased toward RF, by Ian C. Purdie, VK2TIP   http://www.electronics-tutorials.com
The Self Site - Audio circuitry, extensive notes, diagrams by Douglas Self    http://www.dself.demon.co.uk
Circuitry Links Collection - by Tome Loredo, within Electronics resources  http://astrosun.tn.cornell.edu/staff/loredo/ee.html#sim
Audio Circuits To Build - By ePanorama.net   http://www.epanorama.net/audiocircuits.html
Circuit Collection -  By CommLinx Solutions   http://www.commlinx.com.au/schematics.htm
The Audio Pages - Design Information, Projects by Elliott Sound Products  http://sound.westhost.com 
The Class-A Amplifier Site  -  By Geoff Moss   http://www.gmweb.btinternet.co.uk
Bama's Bunker -  Audio Circuitry Links    http://www.eeph.com/~james/schematics_micpreampsmixers.html
Electronic Circuits - Electronics Zone    http://www.electronic-circuits-diagrams.com/audio_circuits.shtml
Carl's Electronics, Inc. - 200 Electronic Kits   http://www.electronickits.com
Electronic Projects for R/C - by John Nooyen    http://www.uoguelph.ca/~antoon/gadgets/gadgets.htm
Cyber Circuit - by PTM        http://www.uslink.net/%7Ecybercir/cirplist.htm
Poptronics Magazine & The Ties Magazine Circuits - for simulation with free demo of  Electronics Workbench   http://www.electronicsworkbench.com
Bowden's Hobby Circuits - Over 100 circuit diagrams, links to related sites, commercial kits and projects, newsgroups and educational areas.   http://ourworld.compuserve.com/homepages/Bill_Bowden/homepage.htm#menu
555 Timer by Ron Harrison - Most extensive tutorial we found on the web about 555 timer http://pace.inesc.pt/~eleII/555tutorial.htm
Timer by Ron Harrison - Most extensive tutorial we found on the web about 555 timer http://pace.inesc.pt/~eleII/555tutorial.htm
Circuit 1          Negative resistor cancels op-amp load.
High accuracy op-amp have a problem driving low impedance loads. One solution is to "cancel" the load. If your resistive load is R and you connect it in parallel with a negative resistor of -R, the resistance of the parallel combination is infinite. Circuit presents a practical application of the concept. 
By EDN Magazine, May 24, 2001, Design Ideas, page 108.     http://www.ednmag.com       jpg 100kB 
Circuit 2          Dual microphones separates voice from noise 
Two microphones placed equidistant from user's mouth on the user's chest produce in-phase signals to this noise canceling circuit's multiplier, separating the user's voice and out-of-phase signals from background noise. Uses AD638 as bipolar 4-quadrant multiplier.
By EDN Magazine, Design Ideas Annual, page 94.    http://www.ednmag.com       jpg 76kB  
Circuit 3          Ultrasound transducers form proximity detector 
Combining micropower op amps with a pair of matched piezoceramic transducers (one optimized for 40 kHz transmission and the other for 40 kHz reception) yields an ultrasonic proximity detector. The detector employs the radar principle - nearby people or objects reflect the transmitter's steady tone back to the receiver. The transmitter is based on ICM7555 timer, while the receiver employs high bandwidth MAX403 op amp.
By EDN Magazine, April 9, 1992, Design Ideas, page 145.    http://www.ednmag.com       jpg 91kB     
Circuit 4          Bipolar circuit stabilizes power 
This circuit solves constant power circuit and works with single supply. It is based on Gilbert's multiplication cell, the circuit is another useful application of translinear circuits. 4 NPN and 3 PNP transistors are used in such configuration that makes the power dissipated in the resistive load constant and independent on load variation.      
By Circuit & Devices, continuation of Nov 1991 circuit. V.A. Piskarev - Severnaya Zarya - St. Petersburg, Russia and L.M. Filanovsky - University of Alberta - Edmonton, Canada 
Circuit 5          Paralleled amplifiers drive quietly
By paralleling amplifiers, you can increase load drive while keeping output impedance low and reducing noise voltage. This circuit uses inverting and non-inverting configuration with 4 op amps. Calculations demonstrate noise reduction.
By EDN Magazine, April 23, 1992, Design Ideas, page 171, by Moshe Gerstenhaber & Mark Murphy from Analog Devices Sem. 
Circuit 6          110 dB Beeper Circuit
Most piezoelectric beeping devices with internal drivers lack sound intensity, only producing 80 dB SPL with 9 V supply. This circuit will produce 110 dB SPL from 9 V battery, using Panasonic EFB-BD32B21 piezo alarm and 74C14 chip.    
By Electronic Design, AUG 5, 1993, page 81, by David A. Johnson
Circuit 7          Cascode circuit works from 1 V supply
Most piezoelectric beeping devices with internal drivers lack sound intensity, only producing 80 dB SPL with 9 V supply. This circuit will produce 110 dB SPL from 9 V battery, using Panasonic EFB-BD32B21 piezo alarm and 74C14 chip.    
By Electronic Design, May 21, 1992, by Ian M Wiles, IPR Technology, Basingstoke, Hants, UK
Circuit 8          Diode simulator reduces forward drop to 0.04V
To gain higher power efficiency, a lower then 0.7V diode drop is sometimes desirable. This simple circuit exhibits a voltage drop of 0.04V with 1A of forward current. Based on low cost op amp (LM393) and MISFIT transistor (IRFZ40), it requires two supplies and provides two terminals: Diode Cathode + Diode Anode. 
By Electronic Design, May July 20, 1992, by Isaac Eng, ESTCO Battery Engineering, Ottawa, Ontario
Circuit 9          Circuit vocalizes telephone number
To gain higher power efficiency, a lower then 0.7V diode drop is sometimes desirable. This simple circuit exhibits a voltage drop of 0.04V with 1A of forward current. Based on low cost op amp (LM393) and MOSFET transistor (IRFZ40), it requires two supplies and provides two terminals: Diode Cathode + Diode Anode. 
By Electronic Design, Feb 3, 1994, by Malcolm Watts, Wellington Polytechnic, Wellington, New Zeland
Circuit 10          MOSFET replaces switch
By using a cheap, readily available MOSFET, you can use a single-pole switch to turn a bipolar power supply on and off without consuming extra power.
Circuit 11          Buffer tree multiplies dc supply voltages
The "buffer tree" can multiply a dc supply voltage by any whole number. The circuit successively adds the supply voltage to itself using a cascadable circuit element. The circuit element comprises two capacitors and paralleled HEX inverters configured as a noninverting buffer. The circuit relies on the bidirectional properties of MOSFETs.  By EDN Magazine, May 7, 1992, Design Ideas, page 201.
Circuit 12          CMOS switches develop negative voltage
The simple negative-voltage converter works over an input range of 3 to 9V with an internal resistance ranging from 2000 to 400 Ohm, depending on input voltage and output loading. By EDN Magazine, July 22, 1993, Design Ideas, page 46.
Circuit 13          Fast buffer splits power supply
The high-speed buffer can sink or source enough current to derive a new, stable output ground, splitting the input supply. The EL2008 used has a 1 Ohm output impedance. The buffer allows the circuit to handle unbalanced load currents that a simple resistive divider could not. By EDN Magazine, July 22, 1993, Design Ideas, page 48.
Circuit 14          Driver isolates itself from transducers
Ultrasonic transducers are part of a variety of circuits such as motion detectors and range finders. One design practice is to operate the transducers as matched pairs of one transmitter and one receiver. Presented circuit is an alternative design practice in which a single transducer acts as a transceiver. By EDN Magazine, July 22, 1993, Design Ideas, page 58 
Circuit 15          Low cost active load draws constant battery power
Unlike nickel-metal-hibride and lithium-ion rechargeable batteries, the discharge voltage of alkaline batteries is not constant and tends to vary from 1.5 to 1.8V per cell. Alkaline-battery manufacturers specify the discharge life of their batteries under constant power loads. Thus the circuit draws a constant power from the battery pack. By EDN, April 13, 2000, Design Ideas, page 210.
Circuit 16          Single stage gives logarithmic gain steps
By placing a variable component in the positive feedback loop of an op amp, you can vary the gain of the stage logarithmically with respect to a linear resistance or conductance. Such a stage could prove useful, for example, in an audio circuit where you need a linear "dB" response. By EDN Magazine, March 3, 1994, Design Ideas, page 98.
Circuit 17          Measuring differential delay with sine squared pulses
"Ripple in a sum signal indicates differential delay". A technique for measuring differential delays among red, green and blue signals transmitted on different parallel channels exploits the sine-squared pulses that are parts of the standard test signals transmitted during the vertical blanking interval of the frame period.  By NASA Tech Briefs, Feb 1994.
Circuit 18          Inverters form three phase VCO
You sometimes need an inexpensive VCO that can produce evenly spaced three-phase outputs over a wide frequency range. Presented circuit produces relatively squarish waveforms and consists of only the 3 inverters. By EDN Magazine, Aug 2, 2001, Design Ideas, page 102
Circuit 19          Get negative rail using CMOS gates
By implementing this inexpensive circuit built with CMOS gates, a negative rail can be obtained from a positive supply. The circuit's input range is 1.2 to 7.0 V, and no load loss is only 1 mV. The negative rail can be generated from one 1.5 V cell.     By Electronic Design, March 28, 1991, Idea for design, page 117.
Circuit 20          Circuit amplifies without amplifiers
The circuit amplifies a dc signal using switches and charge-storage capacitors. It has a fixed gain of 8 and averages the input signal over eight timing periods. 
By EDN Magazine, April 23, 1992, Design Ideas, page 184.  Circuit_amplifies_without_amplifiers_jpg_65kB    
Circuit 21          Build efficient DC Lamp dimmer
A linear voltage regulator scheme is often employed to control dc lamp brightness. This approach is usually worse than 50% efficient. An alternative is the pulse width modulated approach, which can yield efficiency of 96% or better. Prsented circuit forms a narrow pulse generator with a frequency of about 200 Hz, and a pulse width of approximately 0.1 ms. With lamp load of up to 24 W, there is no need for a heat sink.
Circuit 22          Build ultra low dropout regulator
Switching regulator post regulators, battery powered apparatuses, and other applications often require low dropout linear regulators. This simple circuit offers a lower dropout voltage than available monolithic regulators, with 50mV at 1A and 450mV at 5A. The 3 pin LT1123 regulator servo controls base of PNP, power transistor MJE1123.
Circuit 23          Circuit eliminates PC echoes
Long distance telephone services available via the Internet often require the PC user to wear headphones of a headset to prevent echo caused by the microphone's picking up the loudspeaker outputs. Presented circuit eliminates echo while using the existing PC microphone and speakers for a comfortable conversation.
Circuit 24          Ultrasonic range finder uses few components
An ultrasonic,or sonar, range finder is a common sensor in robotic systems and industrial environments. A novel sensor design uses a uC, a few peripheral components, and a pair of ultrasonic transducers. Usable range is about 4" to 16', with accuracy of +/-2".
Circuit 25          5V to 1.8V converter works without magnetics
To derive 1.8V from 5V, you might use a switching mode regulator, very efficient but expensive, linear regulator, low cost but not efficient - or a CMOS charge - pump voltage converter. Presented converter has better than 70% efficiency, sources as much as 100 mA, costs less and takes less space than switching mode regulator.
Circuit 26          Sensor adapts to changing light levels
Presented circuit dynamically adjusts itself, changing long term conditions, while monitoring the transparency of a medium. The circuit has two servo loops: One having a long time constant that maintains a steady level of light excitation through the monitored medium, and another having a short time constant that sets the threshold for detecting sudden changes in the medium's transparency.
Circuit 27          Special Low Pass filter limits slope
Adding several components to a simple first order, low pass filter, helps to create a different yet handy filter. This simple circuit combines a low pass filter with a bidirectional diode clipping network. The result is a filter that will limit the maximum slope (not frequency) it passes.
Circuit 28          Simple sine wave generator has no filters
Generating sine waves with controlled frequencies over a wide range is difficult when using RC or LC sinusoidal oscillators. However, this performance can be simply created using a wideband digital squarewave generator, a counter, and a weighted summing network. Using such principle, a sinusoidal signal with a 100,000,000 to 1 frequency range from about 1 MHz to under 0.01 Hz can be obtained without a need for any low pass or high pass filters. The circuit uses 4040, 4030 and OP77 chips.
Circuit 29          Constant power load needs only a few components
Switching dc-dc converters are often used in portable or battery backed projects because of their broad input voltage range and high efficiency. These converters present a constant power load to the battery - their input current increases as the battery voltage decreases. Presented circuit simulates real life battery discharge scenario, allowing  accurate testing of battery life.
Circuit 30          Comparator has independent trip voltages
For an inverting amplifier with histeresis, 3 resistors determine the crossover voltages. Unfortunately, using 3 resistors to set the upper and the lower trip voltages creates a dependence between the two trip voltages. It's impossible to set one voltage without affecting the other. Open - collector circuit solves this problem. 
Circuit 31          Switched capacitor regulator provides gain
Presented circuit with switched capacitors dramatically increases voltage inverter efficiency, when input voltage is more than twice the desired output voltage, for example using 12 V to obtain 3.3 V. A typical switched capacitor voltage inverter to generate negative voltage from positive voltage is modified to step down regulator with current gain of 2.  By EDN Magazine, March 13, 1998, Design Ideas, page 80.
Circuit 32          Capacitor amplifier reduces ripple without dc loss
Filter capacitors reduce ripple in power supply circuits or provide pulse energy at a constant dc voltage. In both applications, there is fundamental conflict. The circuit needs constant voltage, but energy storage and delivery capability is a function of capacitance and of voltage change squared. To achieve a low ripple output, a large, costly capacitance is needed. The emitter follower circuit boosts the output capacitor effectiveness in reducing ripple, but induces large dc loss. Presented circuits show alternative solutions.  By EDN Magazine, June 6, 1996, Design Feature, page 138.
Circuit 33          Active transformer for audio input
Line receivers with high common mode input impedances clearly produce higher CMRR in real world balanced interfaces. Presented circuit yields high ac common mode impedances yet leaves a low resistance path to ground for dc at the input.  By EDN Magazine, June 4, 1998, Design Feature, page 144.
Circuit 34          1.5V Battery powered fan switches ON and OFF by hand
This circuit represents a very simple and inexpensive alternative to an electrical switch used to turn ON and OFF the battery operated dc motor typically employed in in handheld fans. It eliminates the mechanical components that could suffer from humidity, condensation or bad contacts. You can switch ON the motor by simply giving it a small rotation with your hand. This movement produces a voltage drop between the motor terminals, which is sufficient to activate switching transistor.  By Electronic Design Magazine,  www.elecdesign.com, Massimo Gottardi, Trento, Italy. 
Circuit 35          Short-circuit finder uses few parts
The simple tester detects short circuits on assembled pc boards and also rings out cables and harnesses. It has a narrow zone of threshold uncertainty and very low "insertion" voltage and current. It is not confused by capacitors. Based on LM10, it works with 1.1 to 40 V supply.  By EDN Magazine, NOV 5, 1998, Design Ideas, page 130.
Circuit 36          Low noise voltage source
Measuring semiconductor performance often requires a low noise voltage source. Commercially available power supplies use electronic voltage references and may produce too much low frequency noise to get accurate measurements. Presented simply circuit generates noise two to three magnitude lower compared to commercial power supplies.  By Test & Measurement World, AUG 1998, page 15, www.tmworld.com
Circuit 37          Low frequency oscillator draws only 500nA
The low frequency square wave oscillator is based on CD4007UB and a few passive components. It draws only 0.5 uA from a 6 Vdc supply. It produces about 2 Hz, with available high frequency near 300 Hz. By EDN Magazine, SEP2, 1993, Design Ideas, page 118.
Circuit 38          Capacitive sensor "likes" parasitics
Stray capacitance is a common problem with capacitive sensors. The capacitance changes within the measurement range are normally much smaller than the strays, the result is a loss of sensitivity. Various methods are available to increase relative sensitivity. Instead of, presented circuit uses the stray and turns its drawbacks to your advantage.  By EDN Magazine, SEP 24, 1998, Design Ideas, page 180.
Circuit 39          Potentiometer sets bandwidth, no gain
The circuit allows you to adjust the pulse response (bandwidth) independently of the gain - with a potentiometer in series with the inverting input of a current feedback op amp.  By EDN Magazine, May 11, 2000, Design Ideas, page 177.
Circuit 40          Cable finder seeks out wall conduits
The circuit uses an antenna in the wall and a receiver to locate a cable conduit, useful for brick walls with iron elements. When you debug home electrical wiring, a tool that determines the location of cable conduits comes in handy. Some short range finders are good for brick walls, but not for walls consisting of iron elements. Presented circuit uses an antenna in the wall conduit and a receiver to locate a cable conduit, with 74HC132 and a few easily available parts. The combination can accurately locate the antenna placement.  By EDN Magazine, MAY 11, 2000, Design Ideas, page 178.
Circuit 41          Circuit forms industrial-grade digital potentiometer
This solid state potentiometer simulates a mechanical potentiometer and fits in the same space. It produces a signal of 0 to 10 V, with a few parts involved. The key to the circuit is the low power, digital potentiometer 100 kOhm IC, configured as a voltage divider, providing an output of 32 discrete voltage steps.  By EDN Magazine, SEP 20, 2001, Design Ideas, page 104. 
Circuit 42          Excel offers painless LCD initialization
To display a font or a symbol on an LCD, you need to convert the desired character into numerical data. Creating the data for an entire font set requires specialized tools, even with these tools, the task can be daunting. Alternatively, you can build a font calculator using an Excel spreaddsheet.  By EDN Magazine, SEP 20, 2001, Design Ideas, page 98
Circuit 43          Passive filter cleans up power-line communications
A power line communications system needs input and output filters to eliminate interference. Presented filter uses passive components because of the requirement for low power consumption.  By EDN Magazine, Sep 20, 2001, Design Ideas, page 106.
Passive_Filter_cleans_up_power_line_com_1_jpg_70kB    Passive_Filter_cleans_up_power_line_com_2_jpg_45kB
Circuit 44          Microcontroller selects minimum/maximum value
Microcontroller based systems for measurement, sensor data processing, or control, sometimes require you to determine a maximum or minimum data value. Two approaches presented here use MC68HC705KJ1: Microcontroller stores data values in memory before processing (a), or processes data on the fly (b).  By EDN Magazine, SEP 20, 2001, Design Ideas, page 100.
Microcontroller_selects_min_max_value_1_jpg_69kB    Microcontroller_selects_min_max_value_2_jpg_117kB
Circuit 45          Circuit makes simple FSK modulator
Commercial FSK (frequency shift keying) modulators are bulky and need many passive parts. Presented circuit uses a single inverter, NL27WZ14 gate, to generate continuous FSK date from TTL level signals. When input state changes, a continously running generator changes frequency by introducing an extra capacitor to RC network. By EDN Magazine, Shyam Tiwari, Sensors technology Ltd, Gwalior, India. 
Circuit 46          Circuit detects first event
Presented circuit is a "first event"indicator, like a game show's "who's first to answer" detector. It indicates which of the two momentary switches closes first. The circuit can be cascaded to obtain more channels. By EDN Magazine, May 3, 2001, Design Ideas, page 89.
Circuit 47          Passive filters fill the bill at audio frequencies
Low-frequency filters, particularly at audio frequencies, usually take the form of active filters. They have many advantages, but passive filters remain a viable option when you quickly need low cost prototypes and test pieces. Passive filters require no dc supply and no complex pc boards. By EDN Magazine, Feb 2001, Design Ideas, page 128.
Circuit 48          Circuit improvement on first event detection
This circuit requires less passive components, less expensive ICs and easy scalability, compared to earlier published circuit (EDN, May 3, 2001, pg 89). This is the n-player first event detection circuit with several improvements. By EDN, Aug 16, 2001, Design Ideas, page 106.
Circuit 49          Convert periodic waveform to square waves
Converting periodic waveforms to square waves is an integral part of extracting a clock signal from data, creating waveform generators and making timing-pulse generators. Any square-wave conversion circuit is more valuable when the square wave's duty cycle is variable and controllable. This comparator, integrator and TTL gate based circuit has all these attributes. EDN Magazine, Aug 16, 2001, Design Ideas, page 105.
Circuit 50          Circuit combines power supply and audio amplifier
The circuit presented help if you need to transfer dc power and audio over a pair of copper wires. One application for such circuit is a low cost door opening system with speech input. The circuit uses only one IC, the well known LM317, a low cost power supply. Using the chip, you can modulate the adjustment pin input with the audio signal from an electret condenser microphone. EDN Magazine, Dec 20, 2001, Design Ideas, page 62.
Circuit 51          Supply derives 5 and 3.3V from USB port
Portable devices like digital cameras, MP3 players and PDAs can derive their power from a USB port. This circuit produces 5V and 3.3V, while allowing the port to maintain communications - and charges a lithium-ion battery at a time.    EDN Magazine, Dec 20, 2001, Design Ideas, page 62.
Circuit 52          Transistor tester fits into your pocket
This simply tester allows you to test the polarity and function of a transistor. You connect the transistor, or device under test, between the collectors of an unstable multivibrator. Thus, the Vce voltage of the device under test is alternately positive and negative.  EDN Magazine, Dec 20, 2001, Design Ideas, page 60.
Circuit 53          Analog switch lowers relay power consumption
Unlike transistors, relays' switch contacts are electrically isolated from the control input. However, the power dissipation in a relay coil may render the device unattractive in battery powered applications. You can lower this dissipation by adding an analog switch that allows the relay to operate at a lower voltage.  EDN Magazine, Dec 20, 2001, Design Ideas, page 57.
Circuit 54          Analog - input circuit serves any microcontroller
With two transistor arrays and three discrete components, you can configure an analog front end for a microcontroller. Thus this simple ADC circuit is perfect for getting analog signals into a purely digital microcontroller.   EDN Magazine, Dec 20, 2001, Design Ideas, page 58.
54_A_Supply_derives_5_and_3.3V_from_USB_port_jpg_106kB    54_B_Supply_derives_5_and_3.3V_from_USB_port_jpg_26kB
Circuit 55          Dual digital POT creates accurate, temperature stable amp
The thermal performance of a simple gain circuit using a digital potentiometer in typical configuration is typically 800 ppm/deg C. It can be easily raised to 1 ppm/deg C with presented solution.  Electronic Design Magazine, Dec 17, 2001, Ideas for design, page 59.
Circuit 56          Circuit efficiently switches bipolar LED
Typical switching circuit for a bipolar, two color LED wastes power and does not work with low supply voltage. Improved circuit employes a "flip-flop" switch, the only losses come from the Vcesat and the base currents of the transistors.  EDN Magazine, Nov 22, 2001, Design Ideas, page 98.
Circuit 57          Circuit forms adjustable bipolar clamp
EDN Magazine, Nov 22, 2001, Design Ideas, page 100.
Circuit 58          Analog - input circuit serves any microcontroller
Electronic Design Magazine, Dec 3, 2001, Ideas for design, page 83.
58_A_Simple_LED_flasher_yields_99%_power_reduction_jpg_119kB    58_B_Simple_LED_flasher_yields_99%_power_reduction_jpg_12kB
Circuit 59          Universal  impedance generator handles biomedical applications
Electronic Design Magazine, Dec 3, 2001, Ideas for design, page 84.
Circuit 60          Single gate VHF temperature transmitter runs on 3.6V
Electronic Design Magazine, Dec 3, 2001, Ideas for design, page 86.
Circuit 61          Build your own bypass capacitor tester
EDN Magazine, Dec 6, 2001, Design Ideas, page 116.
Circuit 62          Circuit compensates optocoupler temperature coefficient
EDN Magazine, Nov 22, 2001, Design Ideas, page 93.    62_Circuit_compensates_optocoupler_temp_coefficient_jpg_110kB
Circuit 63          Improve FET based control
EDN Magazine, Dec 6, 2001, Design Ideas, page 112.
Circuit 64          Noncascaded arrangement optimizes bridged amplifiers
Electronic Design Magazine, Nov 19, 2001, Design Ideas, page 87.
Circuit 65          Thermostat for high altitude atmospheric sampler is fault tolerant
Electronic Design Magazine, Nov 19, 2001, Design Ideas, page 88.
Circuit 66          Manually operated digital pot is revisited
Electronic Design Magazine, Nov 19, 2001, Design Ideas, page 90.
Circuit 67          Circuit converts pulse to voltage
Electronic Design Magazine, Oct 25, 2001, Design Ideas, page 92.
Circuit 68          Short dc power line pulses afford remote control
EDN Magazine, Oct 25, 2001, Design Ideas, page 94.
68_A_Short_dc_power_line_pulses_afford_remote_control_jpg_101kB  68_B_Short_dc_power_line_pulses_afford_remote_control_jpg_81kB
Circuit 69          Circuit forms efficient cosine calculator
EDN Magazine, Oct 25, 2001, Design Ideas, page 87.
Circuit 70          Reference stabilizes exponential current
The use of matched transistors balances the first order temperature coefficient but leaves temperature dependent gain term q/kT. Clasic antilog circuits use a thermistor in the drive circuitry to correct this temperature dependency. However, you can achieve an exact temperature correction by adding a second reference transistor. With 3 op amps,  3 transistors and  a few passive components, presented circuit forms a temperature independent antilog - ratio circuit.  EDN Magazine, Oct 25, 2001, Design Ideas, page 88.
Circuit 71          Low cost relative humidity transmitter uses single logic IC
The low cost percentage - relative - humidity radio transmitter operates in a cold storage warehouse for vegetable storage at temperatures of 1 to 5 deg C. It uses a single 74HC132 chip and a few passive components forming a humidity controlled transmitter for 10 to 50 MHz RF band.  EDN Magazine, Oct 25, 2001, Design Ideas.
Circuit 72          Log amp uses capacitor charging law
The novel logarithmic amplifier relies on the exponential charging characteristics of a simple RC circuit and uses popular timer 556 timer (LM556C) with a few components.  EDN Magazine, Jan 10, 2002, Design Ideas, page 71
Circuit 73           Extend the timing capabilities of a PC
When you use internal timing registers and under DOS, a PC cannot easily measure time intervals with better time resolution than a millisecond. Measuring long intervals even with this precision is a waste of many CPU cycles. A microcontroller is well suited for this task, allowing extending timing precision into the microsesond range for periods from tens of microseconds to more than 24 hours. This simple circuit uses PICI16F84 drawing only 2 mA, two capacitors and a 4 MHz crystal.  EDN Magazine, Jan 10, 2002, Design Ideas, page 72
Circuit 74           Optocoupler simplifies power line monitoring
Even if you suppose the ac power line to be free of dc voltage, some types of loads drain dc currents, thereby introducing a small dc voltage because of voltage drops in the ac lines. This design goal is to obtain a stable dc voltage at the output. Thus processor can compute true-rms voltages and currents, apparent and active power plus power factor.  EDN Magazine, Jan 10, 2002, Design Ideas, page 76
Circuit 75           Improved amplifier drives differential input ADCs
ADCs with differential inputs are becoming popular. Still some gain is required between the signal source and the ADC. Frequently used amplifiers have only single output. Presented simple circuits provide dual outputs. EDN Magazine, Jan 10, 2002, Design Ideas, page 80
Circuit 76           Circuit forms dc motor switch with brake       
Controling a small dc motor without speed control causes a few problems. Because of the inductive load and the low starting low starting resistance of the motor, the switch tends to wear prematurely,  with all the related sparks and EMI problems. More, when you cut the power, the motor continues to rotate for a certain time, depending on its initial speed and inertia. Presented circuit with two transistors is very simple and provides enhanced deceleration.  EDN Magazine, Jan 10, 2002, Design Ideas
Circuit 77           Circuit measures small currents referenced to high voltage rails 
Designs that need to measure small signals riding on high voltage power rails suggest the use of isolation devices. However, a high common mode voltage instrumentation amplifier used with a rail to rail input and output (RIO) amplifier can recover the signal cleanly and at a much lower cost.  Electronic Design Magazine, Jan 7, 2002, Ideas for Design
Circuit 78           Sorry, under construction

Circuit 79           Low power keypad consumes only 100nA
Sometimes one or more keys become "stuck" or are being pressed. Depending on the circuit design and implementation of the keypad interface, this condition could cause excess current to flow, thereby draining the batteries in portable equipment. Presented circuit solves this problem by using a n ultralow power microcontroller. EDN Magazine, Jan 24, 2002, page 86, Design Ideas 
Circuit 80           Autoreferencing circuit nulls out sensor errors
The circuit nulls out the error of a sensor, such as a pressure transducer, at its reference level - for example, at ambient pressure. The circuit is an analog - digital - feedback control system that uses a digitally programmable potentiometer to provide the variability.  EDN Magazine, Jan 24, 2002, Page 85, Design Ideas
Circuit 81           Circuit provides reference for multiple ADCs
The achievable accuracy for systems with multiple ADCs depends directly on the reference voltage applied to the ADCs. Often large number of ADCs are organized in groups of 16, 24, 32 and so on. To obtain maximum accuracy, you need to minimize errors in the ADCs path. Presented circuits demonstrate dc voltage references with ultra low noise. For example, such low noise circuit can drive as many as 1000 ADCs for ultrasound applications. EDN Magazine, Jan 24, 2002, Page 92, Design Ideas
Circuit 82           Temperature sensor circuit provides dual slope output
The excellent linearity of intergrated - circuit temperature sensors make them ideal for direct analog compensation of the thermally induced errors in many circuits. Additionally, some circuits exhibit a positive temperature coefficient in one temperature range and negative coefficient on another. One example is the frequency drift of XT cut crystals, which have a parabolic curve with the center frequency typically specified at 25 deg C. Presented compensation circuit is simple and provides dual slope temperature compensation, with only 3 ICs:  LM19, LM61 and LM4041-1.2.   Electronic Design Magazine, Jan 21, 2002, Ideas for design, page 51.
82_A_Temperature _sensor_circuit_provides_dual_slope_output_jpg_229kB
82_B_Temperature _sensor_circuit_provides_dual_slope_output_jpg_101kB
Circuit 83           Excel formula calculates standard 1% resistor values
Presented Excle formula calculates the nearest standard 1% resistor value without using a lookup table or macro. Type or electronically paste presented formula text into any cell, other than A1. The formula will calculate the nearest 1% resistor for the value in cell A1.  Electronic Design Magazine, Jan 21, 2002, Ideas for design, page 52.
Circuit 84           Wideband filter only has two different components
Wideband filters with bandwidths in excess of an octave can be created by cascading a high pass and a low pass filter. In this design idea, nine pole high pass and low pass filters have been constructed using a modified equal element design, with all capacitors being identical and all inductors having same values as well.  Electronic Design Magazine, Jan 21, 2002, Ideas for design, page 54.
Circuit 85           Composite instrumentation amplifier extends CMRR frequency range 10x
While all instrumentation amplifiers perform well at low frequencies, their ability to reject common signals usually degrades rapidly as the frequency increases. A simple solution to this problem exists. Electronic Design Magazine, Feb 4, 2002, Ideas for design, page 65. 
Circuit 86           Negative resistance nulls potentiometer's wiper resistance
While almost always called "potentiometers" (which are technically defined as three terminal variable voltage dividers), many "pots" actually end up being used as variable resistors (rheostats) instead of. When used as a variable resistor, all potentiometers - whether electromechanical or electronic - suffer from the parasitic error of "wiper resistance". Earlier presented solution "Active cancellation of potentiometer wiper resistance" in Electronic Design, June 14, 1999,p. 104 was not compatible with applications requiring potentiometer's both ends available. Presented here circuit does not suffer from such limitation. Electronic Design Magazine, Feb 4, 2002, Ideas for design, page 66.
Circuit 87           Cross-Trigger Two Oscilloscopes To Create A Delayed-Sweep Display
Many oscilloscopes lack a delayed-sweep function. Cross-triggering two standard scopes produces both main and delayed-sweep displays. This double system offers both main and delayed-sweep traces on every shot, an essential feature for single-shot work. In contrast, the dual-trace units supplies one of the two traces, alternately.  Electronic Design Magazine, June 10, 2002, Ideas for design, page 97.
Circuit 88           Sampling Peak detector has shutdown feature
You face a serious problem with using a slow ADC with a fast peak detector. Presented circuit allows a slow ADC to measure a fast, sampled signal peak. The 100 MHz peak detector for ultrasonic pulse sampling uses a fast MAX4231 amplifier, which amplifier has shutdown feature that facilitates power savings without loosing the sampled signal. The circuit prevents sampling of another input peak before a measurement takes place. This feature helps a slow ADC to monitor a high-speed sampled peak in a desired sampling intervals, an impossible operation with a conventional peak-detecting circuit.  EDN, May 16, 2002, Design Ideas, page 100.
Circuit 89           Remote Humidity Sensor Needs No Battery

Circuit 90           Improved Frequency Modulator Uses "Negatron"

Circuit 91           Circuit Improves Further On First-Event Detector

Circuit 92           Differential Amp Needs No Power source

Circuit 93           Switching Regulator Forms Constant Current source

Circuit 94           Voltage To Current Converter drives White LEDs

Circuit 95           Circuit Controls Two LEDs With One Microcontroller Port Pin

Circuit 96           Add CAD Functions To Microsoft Office
Circuit 97           Dual Gate Inverter Oscillator Saves Power, Boosts LED Brightness

Circuit 98           Circuit performs high - speed voltage - to - current, current - to current conversion

Circuit 99           Linear power driver works from single supply

Circuit 100         PC and long baseline chronography measure ballistic parameters acoustically