If you revamp and update this device, you could submit it to the Design Gadget Freak column. We pay $500 for complete Gadget Freak entries. If you're interested, send me a note at email@example.com and I'll send along the details.
Nowadays, I would update the power supply with a voltage regulator IC and update the op amp, but I think you'll like the simplicity. Hint: two precision thermistors, a 25-turn pot and a voltage comparator op amp.
I grew up on Popular Electronics. Every project was very well documented with schematics and wiring diagrams and parts lists. I seem to see too many of these GF articles not even up to the standards of PE in the good old days - 50's and 60's.
This column needs to be presented with better editing. I agree that many of these GF cases are incomplete and have indecipherable or incorrect schematics and incomplete parts lists like this one and dead end links. Even Design News has had too many errors lately.
I know the audience is full of engineers but who needs to have work so hard to read the article? When these projects are presented with a half baked presentation it is disrespectful to the author and to the readers. And a pain in the @ss to read. It takes the fun out of it.
So PLEASE put a little time into editing and put everything, photos, schematics, BOM's etc into the article on the same page or have links that work.
I found that a far simpler means of solar water heating was to submerge a black plastic sheet in the pool when it was not in use. The sheet did ned to be well below the surface, so as to heat a larger volume of water, it could even be on the bottom, out of the way. It was not hard to remove for serious pool use, and it consumed no energy, and it was very cheap.
Most gadget freak write-ups, it appears to me, are incomplete in one way or another. The result is that the missing order number for the dual temperature controller is to be expected. Just attempt to find a circuit, or some other critical build information. Usually some vital information is missing. That is what to expect.
Using wireless chips and accessories, engineers can now extract data from the unlikeliest of places -- pumps, motors, bridges, conveyors, refineries, cooling towers, parking garages, down-hole drills and just about anything else that can benefit from monitoring.
With strong marketplace demand for qualified engineers across the board that currently outstrips the available supply, there may never be a better time for engineers and project managers to advance their careers and salaries. Whether those moves are successful in the short-term and long-term is likely to depend on how the transition from one job to the next is handled.
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