If you're a reader of EDN Design Ideas, then you know it's been a useful resource for many years. With the birth of an online version in the late 1990s, Design Ideas became a lively forum for engineers to analyze, scrutinize, criticize, and praise many designs. Some of those circuits were designed for test and measurement. I've compiled a list and will summarize a few.
I was the Design Ideas editor from 2008 to 2011, so you might see my name on a few of the links here. If you'd like some insight into what that was like, see the comments in Design Ideas: A Wealth of Circuits.
Would you like to submit your own Design Idea? Then see the Design Ideas Submission Guide by current editor Michael Dunn.
Here are some circuits used for test and measurement:
Measure resistance and temperature with a sound card shows you how to use a sound card's line output to provide excitation for a thermistor. You can then use the card's input to capture the voltage across the thermistor and digitize the result. Remember that sound cards work on AC signals only, so you'll have to provide an AC signal from the sound card's line output. A sound card wonít be as accurate as using a data-acquisition card, but you'll save several hundred dollars. If you donít want to risk using your PC sound card's inputs, you can get a USB audio interface instead.
Figure 1: A circuit from "Measure resistance and temperature with a sound card" by Zoltan Gingl and Peter Kocsis, published May 26, 2011.
Not all cables are made of copper; some use fiber, and sometimes a quick check is what you need. The circuit in LED flasher checks fiber-optic strands uses two high-intensity LEDs (by 2010 standards, anyway) to shine light through fiber-optic cables. The circuit uses a binary divider driven by a 5Hz clock that's divided by two to produce a 50 percent duty-cycle pulse at 2.5Hz. The author shows the circuit with one red and one yellow LED, which makes them distinguishable to most people. As for me, I had some problems with the LEDs on a commercially available cable tester.
Figure 2: A fiber-optic tester verifies connections. By Edwin A Mack, published January 7, 2010.
The design in Circuit measures battery capacity is unusual in that it uses an electromechanical clock to measure discharge time. Of course, you need not use such an old device, but it has one real advantage over electronic clocks: built-in memory. The circuit uses an LM358A comparator to compare the battery voltage against a reference voltage. When the battery drops to that point, a relay opens and the clock stops. The beauty of an electromechanical clock is that it displays the time even after power is removed. Try doing that with an electronic clock.
Figure 3: This circuit by Vladimir Oleynik uses an electromechanical clock to measure a battery's charge time. Published June 9, 2011.