This column usually focuses on prosaic and proven applications for circuits and sensors. This month, though, I am going to talk about an emerging field called evolvable hardware, which potentially has tremendous applicability to designing robust sensing and control systems.

The Ultimate Sensor Nov 1, 2006 By: Ed Ramsden

In the original Star Trek series, DeForest Kelley played ship's surgeon Dr. Leonard McCoy. This character was especially memorable for his frequent medical pronouncement, "He's dead, Jim," and for his handheld medical scanner, a device that looked like a pepper shaker with a spinning cap. This magical sensor could instantly and noninvasively diagnose any medical condition.

Synchronous detction can be used to recover very small signals buried in lots of noise.

With the recent introduction of cheap ?? analog-to-digital converters (ADCs) offering resolutions of 24 bits or more, you'd think that the digital revolution is complete, and that the need for analog design has passed. Twenty-four bits gives you a resolution of better than 1 ?V on a 10 V span, so these high-resolution converters will make it easy to solve many interfacing problems with a minimum of additional circuitry.

Last month we discussed a number of simple passive filters in both low-pass and high-pass configurations. Although these filters could reject out-of-band signals, this capability was relatively limited because they all had an attenuation roll-off rate of –20 dB/decade. You will find that many applications require a much greater ability to reject out-of-band signals than that provided by the passive low-pass filters we looked at.

Back in the late 1970s comedian Don Novello (a.k.a. Father Guido Sarducci) had a routine called the "Five-Minute University," which was supposed to impart to you, in the span of only five minutes, all the knowledge you would retain five years after graduating from a regular university. So, in the same spirit, I offer "Dr. Ed's Five-Minute Analog Filter Design University."

In 1834 Jean Peltier discovered that running an electric current across a junction of two dissimilar metals caused heat to transfer across the junction, cooling one side while heating the other. Because of the low efficiency of this effect in metals, and their high thermal conductivity, which causes heat to rapidly leak back across the junction, this Peltier effect was little more than a laboratory curiosity.

Lately I have been building, debugging, and using different data acquisition (DAQ) systems for various purposes. In the course of this work (especially the debugging!) I started wondering about some of the "available options"—a code phrase for "How would I have done this if I had known what kinds of problems I would be in for with my present design?"

Instability, at least in simple linear systems, results from two characteristics of the control loop.

How much hysteresis you need is a function of the process requirements and control system.