Saturday, November 25, 2017

Paradise ponders: this 'n that edition...

Paradise ponders: this 'n that edition...  A few days ago Debbie and I took a drive over the mountains west of Clarkston, Utah – there's a pretty road there that we quite enjoy.  I took some photos along the way, of Debbie meeting a couple of horses:

A day earlier I caught this nice sunset over the field north of our house, with our valley dark but the Wasatch Mountains to our east still lit.  We'll have lots of beautiful sunrises and sunsets in the winter months...

And finally, here's the current state of my fan controller computer. :)  This is sitting on my desk right now, beeping and booping away. The larger board is a Raspberry Pi 3B computer.  To the right and below it in the photo is a small board with four bits of digital I/O controlled by a PCA9536 chip.  One of those bits is attached to a relay.  I'll use one for a signal switch input, and two for LED outputs.  The small board to the right and up from the Pi is a two-channel 4-20 ma sensor receiver, based on an ADS1115 A/D converter chip.  That chip is a mind-boggler for this ancient electrical engineer: it's a delta-sigma converter with 16 bits of resolution, handling up to 8 conversions per second.  On the same chip is a 4 input multiplexer and a precision voltage reference.  That's far better performance than the refrigerator-sized, million-dollar units I worked on in the Navy in the '70s - and this one cost about $4 and is the size of the head engraved on a U.S. dime.  The blue circular widget above the Pi is another little marvel.  The three leads on the top go to a standard PT100 thermistor for precision temperature measurement.  The electronics in the blue widget linearize the thermistor and produces a 4-20 ma signal proportional to the temperature measured.  I'll have two of those thermistors, two of the blue widgets, and the two-channel 4-20 ma sensor receiver - total price under $40, giving my little Raspberry Pi dual temperature measurements accurate to +/- 0.5 °C (roughly 1 °F).  What an amazing world we live in, where just about anybody can afford to make something like this!

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