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Back in 86 while working for

Back in 86 while working for Dave Ziembicki who had run the HW lab at CBM in King of Prussia, and who went on as a founder of Great Valley Mfg for Amiga stuff, I designed a "Pool Alarm" for detecting if someone fell in a swimming pool.  Terry Ryan (Basic for Plus4 and C128) did the code where we "learned" the pool signature including floating toys and slapping ropes, and then would trip when the signature changed suddenly outside of the limits of deviation we established.
While testing this I found I could model everything in a "air pool" and get less wet.  Before too long I hung the air sonar array on the back of the company car and went for a ride.  By the end of the week I had hooked an LM3914 bargraph display and I could back up by looking at the display.  We also made a blind spot detector with sonar by building it into the running lights of semi-trailers. 
So in effect I designed the backup alarm found on cars today, Dave was in an patent fight with Ford according to "On the Edge".  It's funny when I go to buy a new car and the salesman tells me how the backup alarm works... there really isn't a meaningful way I can say "yeah I designed it"...lol.
A while back I picked up a couple of water transducers, I was thinking about recreating the product as the patent for the pool alarm has expired (actually filed by someone else in Florida if I remember right) and I was thinking about recreating the project using an Arduino and releasing to open source.
Bil Herd

how about recording the input as well?

depending on  where the installation will be why not tie the reciving part of the sonar transducer into the input of a sercurity DVR system?
how knows it could be a humorus ending to where the bubbles come from in the pool!
or taking a 50KW output transducer, and dumping 50KW/h into it with a 1Khz/sec swept pulse!
Speaking of pools, why didn't Bacqusil ever catch on?

One of the things I thought

One of the things I thought to do was to start with a high freqency then drop to low so I could find the front of the pulse which I ended up not needing.  I found out that that technique is called "chirping".  Lol, back then you had to get your hands on a LOT of books to delve in doifferent field.

I remember making several

I remember making several trips to the Morris County and Randolph Library as a kid, and getting frustrated by the lack of useful information.

lol... I found texts by the

lol... I found texts by the US Navy that had way more than I needed in the way of useless stuff for small scale.  I found most of teh usefull stuff by reading between the lines in my big pile of PLL app notes and then sensor/analog app notes in general.

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