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15 May 2018, 10:35

Wandering between the current and the past

It all started with an email from Texas Instruments with a new ebook available: 32 little op amp lessons which, although I have only skimmed through, has some great tips and reinforces some of my experience in the real (analogue) world. Well worth a read!

But a topic that caught my eye was regarding the black line on the end of some non-polarised capacitors, what does it mean? Read the article for details (see section 9 and the link provided) and the possible implications. But it basically marks what lead is connected to the outside of a tubular axial capacitor. Depending on which way it is connected in a circuit it could couple noise into a sensitive node - I had never been aware of this and wonder if that had an impact on any of my previous sensor interface designs?

This moved me back in time to a centrifuge controller. We were asked to modify one for a much slower and stable speed. So a search of the databooks (no internet available then!) and a possible integrated circuit was identified - design complete and successful - job done.

No! It was noticed that an electrolytic was the wrong way round, a big "no-no"! It was a radial type and to avoid damaging the PCB the leads were cut close to the component and then the leads easily extracted. A new component inserted (correctly) and the centrifuge tested before delivery - the speed was no longer constant...

Cutting a long story short it was never resolved, various capacitors were tested with the correct and incorrect polarity connection, even the original was replaced without success. No damage or faults could be found, but due to time pressures it had to be delivered and the best of a bad situation was supplied.

This one (of a few) has always played on my mind even though it occurred in 1980's.

Share your experiences, good or bad!

A keen electronics design engineer with experience in many areas, Spent 30 years in a science environment providing technology solutions to enable scientists to optimally perform their work. Has involved every type of component I can think of! From fempto amps, 5kV supplies, Liquid Nitrogen cooled PIN diodes and CCD's, micro power components for portable applications and class 4 argon lasers. Looking back I was privileged to be a paid 'hacker' with interesting projects to design.

15 May 2018, 10:35