W. Stephen Woodward
Write for Electronic Design
W. Stephen Woodward, independent consultant, holds a BS (with honors) in engineering from Caltech, Pasadena, Calif., and an MS in computer science from the University of North Carolina, Chapel Hill.
Email address: eecon@email.unc.edu
70 results found for W. Stephen Woodward, displaying items 1 - 20

 

July 23, 2009   [Ideas For Design]
Sample 64 Temperature Points For Pennies Per Channel With Multiplexed Delta VBE Thermometry
Delta VBE ( VBE)-based thermometry is based on the “PTAT VBE effect,” which says that for an ideal transistor, the VBE corresponding to changes in collector current is exactly proportional to absolute temperature. Cheap small-signal transistors conform closely enough to the ideal model that VBE circuits can implement accurate and cost-effective thermometers needing no calibration. An earlier Idea for Design...

June 25, 2009   [Ideas For Design]
Triple-Current-Modulation Delta VBE Thermometry Cancels Ohmic Error Sources
Delta VBE-based (VBE) thermometry1,2,3,4 is based on this classic bipolar junction I/V/T relationship: For an ideal transistor, the VBE corresponding to ratiometric change in collector current (I2 / I1) is exactly proportional to absolute temperature: VBE = 198.4 µV * °K * LOG10(I2 / I1). Because cheap, common, and robust small-signal transistors conform closely to the ideal model, circuits that exploit the “PTAT (Proportional...

February 26, 2009   [Ideas For Design]
Isolated Receiver/Converter Uses Multichannel Opto-Isolator
The accurate transmission of analog signals over long distances in noisy industrial environments is a difficult design problem. One of the oldest solutionsisolated current loopsis still one of the best. This Idea For Design presents a simple optically isolated linear current loop receiver that uses generic parts. The receiver operates from a single non-isolated power rail (12 V) to generate a convenient analog 5-V voltage-mode output that’s ready for further...

October 2, 2008   [Ideas For Design]
Use IFDs To Develop And Showcase Your Design Concepts
Electronic Design published my first Idea for Design, “AC-DC Converter Runs Off One Power Supply” (April 16, 1992, p. 93), more than 16 years ago (Fig. 1). It set a theme that I have continued to employ ever since—using the nifty venue of IFDs to present and develop new circuit design ideas and themes to the engineering community. Over the years, examples of some of those basic concepts and ...

October 2, 2008   [Ideas For Design]
Bidirectional H-Bridge DC-Motor Motion Controller: Backstory
IN APPLICATIONS REQUIRING ABSOLUTE accuracy in the speed control of dc servo motors, there’s no substitute for the traditional tachometerbased feedback loop. But for somewhat less demanding situations, adequate accuracy often can be achieved without the complication and expense of a tach. This can be done by taking advantage of the built-in electromechanical constants of the motor itself. For example,...

October 2, 2008   [Ideas For Design]
"Take-Back-Half" Convergence Algorithm Stabilizes Microhydro Turbine Controller
THE SOARING COSTS OF fossil fuels, combined with environmental concerns like climate change, are driving the increased interest in renewable (“green”) energy. No energy source is “greener” than hydroelectric power, particularly small (“microhydro”) installations that involve minimal artificial water impoundment and associated environmental impact. Even with an adequate water source, however, efficient and cost-effective implementation of appropriate...

September 25, 2008   [Ideas For Design]
Optically Isolated 4- To 20-mA Current-Loop Transmitter Is Accurate, Inexpensive
Galvanically (that is, optically or electromagnetically) isolated 4- to 20-mA current loops offer robust noise immunity and tolerate long cable runs. These advantages, combined with simple unshielded two-wire cabling, make this mature signaling standard popular for transmitting analog data in noisy industrial and process control environments. Unfortunately, the conversion of an analog voltage output to an isolated current-loop signal is relatively complicated. In...

September 11, 2008   [Ideas For Design]
Portable Airspeed Measurement


October 28, 2002   [Ideas For Design]
Hyperbaric Fall-Time Viscometer Is PC-Based
The measurement of the viscosity of solutions is an integral element in analytical chemistry and chemical manufacturing. It has particular value in designing and controlling the processes of polymerization, an essential step in the production of...

July 22, 2002   [Ideas For Design]
PC And Long-Baseline Chronography Measure Ballistic Parameters Acoustically
Ballistics is an ancient art—one that was already old when longbows, catapults, and bronze smoothbore cannons were the high-tech missile projectors of their respective day. "External" ballistics undertakes the prediction of the trajectory of the...

April 29, 2002   [Ideas For Design]
PC-Controlled Current Source Supplies 100-V, 1-A, 16-Bit Pulses
The current source shown in the figure is designed to support toroidal-cavity nuclear-magnetic-resonance electrophoresis (TCNMRE) measurements of molecular electrical mobility in chemical samples. To do so,...

February 4, 2002   [Ideas For Design]
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. When used as a variable resistor, all...

November 19, 2001   [Ideas For Design]
Thermostat For High-Altitude Atmospheric Sampler is Fault-Tolerant
Among the many measures of good circuit design (e.g., cost, performance, and efficiency), none is more important than reliability. Usually, adequate expected reliability can be achieved by simply sticking to conservative design rules and good...

October 29, 2001   [Ideas For Design]
Measure Projectile Velocity Optically With An Ohmmeter
Archery and target shooting with firearms and air guns are just a few of the many sports and pastimes that involve high-speed projectiles. A handy accessory for any of these activities is some means of accurately measuring the speed of the...

August 20, 2001   [Ideas For Design]
16-Bit PWM Optoisolated DAC Is PC-Controlled
There was a time when an "honest" (e.g., DNL < 1/2 LSB) 16-bit digital-to-analog converter (DAC) was an expensive, premium component. Nowadays they're almost jellybeans—almost. Some applications, however, can still benefit from multichip...

July 9, 2001   [Ideas For Design]
"Take-Back-Half" HVAC Thermostat Is Precise And Energy-Efficient
Implementing tight control of environmental temperature is essential in many critical areas. For instance, it's necessary when research laboratories house sensitive instrumentation and for manufacturing facilities involved in high-precision...

June 4, 2001   [Ideas For Design]
Decompensated Op-Amp Gain Is Adjustable From Zero To Open-Loop
Over three decades ago, the internally frequency-compensated, monolithic op amp was introduced. Since then, many of these devices have been made available in two variations. While both versions are designed to maintain the same dc parameters, they...

May 7, 2001   [Ideas For Design]
Series-Connected Transistors Use Differential Heating To Sense Airflow
Among the methods available for airflow measurement, thermal flow meters enjoy the virtues of simplicity. They also offer simple construction, low cost, and superior sensitivity to low flow rates (less than 1000 fpm). All thermal anemometers make...

April 2, 2001   [Ideas For Design]
Digital-To-Analog-Resistance Converter Is Optically Isolated
The subject of digital-to-analog converter (DAC) applications is generally rather tame. It's usually confined to a boring discussion of settling time, the number of bits of resolution needed, the virtues of serial or parallel interfaces, and whether...

March 19, 2001   [Ideas For Design]
Precision Thermostat Uses TBH And AC Feed-Forward Compensation
Precision temperature control with relatively high-power heaters driven directly from unregulated "120-V" ac lines is an efficient, inexpensive way to manage large thermal loads. A number of annoying complications can render this straightforward...





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