New pulse patent by mr Johnson!

Interesting times! Look up patent
US 9366778 b1

Maybe someone can post link? I don't know how to do it.

John

Exciting times indeed!!

Link: PI Metal Detector with Quasi-Resonant Transmitter and Associated Method

Interesting read, he appears to be focusing on a re-circulatory DC PI circuit that will lessen the need for the ginormous battery systems (and weight) typically associated with PI systems. If you have an abundant amount of time on your hands, it makes for an interesting read as he contrasts several other PI designs from various manufacturers (including his own PI design).

Interesting that Dave filed three PI circuit patents in the mid-late 80's. What company were those for? Not sure when he went to work at Fisher?

-Brian

Brian ,,,Dave has said before he designed a pulse for Fisher in the 80s..it became the impulse..say the Impulse was a stepped down watered down version of what he designed..he stated he had built a discriminating pulse unit but the higher ups at Fisher decided to cut the corners and gave us the Impulse..

Keith

Here's Dave's story on it.

___________________________________________________________________________________________________________________________________________

"Back in the early 1980's, Jim Lewellyn (then the president of Fisher) got the idea that he wanted a fully static ground balanced discriminator. At that time I was prototyping multifrequency stuff and told him that motion was the way to go, we'd already proven that with the 1260-X. But he kept on begging for fully static operation, and I'd heard a thing or two about PI (although not seen any schematics or had a PI unit in my hands) and figured that with PI you could do it fully static-- again, not that I thought fully static discrimination was a good idea. His answer to my proposal to develop a PI fully static discriminator was simple-- "PI's are no good." He didn't know any more about PI than I did, but that much he was certain about.

So I figured out a way to build a PI and started bootlegging them when the boss wasn't looking. After a few rounds of prototyping I finally had something that worked-- not well, but at least well enough to illustrate proof of principle. Jim didn't want to talk about it. So, I realized I was going to have to trick him into capitulating.

I built a PI that looked straight out of an old-fashioned hillbilly cartoon. I wound the searchcoil around the rim of a wicker basket, tied it to a branch pruned from a sycamore tree, put the electronics in a little wooden dried codfish box minus the codfish on the other end of the stick, wired the searchcoil to the box with lamp cord, and instead of a real knob on the threshold control I glued a Pepsi bottlecap. Our graphic artist made a label for it that said "CodFisher". And, it really worked, fairly well by the PI standards of that time. About 7-8 inches on US coins, more like 6 inches in disc mode which was just a long pulse delay that lost everything below zinc pennies although iron still came through.

I took it down to the local fish store and worked out a deal with the proprietor Olga. We put a tag on it that said $10, and she put it on top of refrigerator out of sight of the public. If someone walked asking to take a look at a funny metal detector, she'd take it down and they could take a look. And if they wanted it for ten bucks, sell it to 'em for ten bucks and keep the ten. The kicker is that the only person besides me and her who would know it was there, would be Jim Lewellen, because I'd tell him. I was a regular customer and she was willing to have some fun, so it was a deal.

I told Jim that I'd seen a weird beep at the fish store of all places, he oughta drop in after work and check it out. He ignored me, and it, for two weeks. Finally he said, "Dave, I know you're up to something, just tell me." I told him, "Yep, I'm up to something, but the only way you'll find out what, is to go to the fish store." He went, saw it, cracked up, paid his ten bucks, tried it out, and that was the end of "PI is no good".

Several prototypes later we had ourselves a design that was almost ready for production. Fully static with discrimination, meter target ID, and manual ground balancing. He thought it was great and was shocked when the distributors told him they didn't want it. From that disaster emerged the Impulse for underwater work, and a return to multifrequency for land machines which led to the CZ which is still in production virtually unchanged.

The Codfisher-Impulse type PI's were patented together with multifrequency back in the late 1980's (award may have been early 1990's, I don't remember). Simple circuit, ran on a single 9 volt battery, fully static, stable, easy to add discrimination and ground balancing capability, no high voltages, no earth field pickup problems. I suppose that someone's published the Impulse schematic over on Carl's Geotech forum. The thing is so easy to build and get working right that I'm surprised that the hobbyist PI folks never took any interest in it. It's a lots better hobby project than the stuff I see them screwing around with over there.

From a commercial perspective, the end of the Impulse was the end of the Johnson PI platform. Within its limitations it works surprisingly well, but I know enough about its limitations not to be tempted to resurrect it.

--Dave J."

“I don't care that they stole my idea . . I care that they don't have any of their own”
-Nikola Tesla



Edited 2 time(s). Last edit at 08/20/2016 08:51PM by Keith Southern.

Says 22us with 5khz in the article? Hmm maybe it's a hybrid detector?

John