A quick plug for a little gem of a book that all fans of early radio should know about: "Super-Regenerative Receivers" by J. R. Whitehead (Cambridge University Press, 1950).  It's part of the Modern Radio Techniques series, where a bunch of the technical movers and shakers document the advances that were made during the war, e.g. centimeter radar.  This one is about the theory and practice of superregenerative radios.  I learned a lot from it and had a lot of fun.

Temperature Control

The need to control temperature is everywhere, but getting it right is more difficult than one might expect. A domestic furnace controlled by a simple thermostat keeps a house comfortable in winter, but the inside air temperature swings irregularly over a range of a few degrees. That's fine for a house---you can have a New Year's party, with a bunch of people dissipating a hundred watts each, doors to hot ovens and the cold outside opening and closing, no worries whatsoever.  The heating system keeps it comfortable.

In a previous article, we described an ultralow-cost time-domain reflectometer (TDR) that  is used as a radar dipstick for fuel gauges in heavy equipment.  Its 150-ps edges were better than good enough, and its rock-bottom BOM cost ($1.30 @ 100 pcs) made it possible for the whole gauge to retail for under $40.  That performance is far from the limit for low-cost samplers, as we'll see.

One of the most enjoyable parts of electronics design is getting excellent performance with rock-bottom parts cost.  The right circuit can produce exceptionally good speed, noise, and accuracy specs from very low-cost parts.  A case in point was a project from December 2016: a time-domain reflectometer (TDR) for a liquid level sensing application in industry.