Bidirectional logic level shifting from positive to negative supply

USB JTAG interface + USB isolator.

Can't you wait until all the fire engines have cleared out? :-)

He's like JF, eager to catch me doing something wrong. He guards against himself being wrong by doing nothing. Seems effective.

Brainstorming in public is something most people won't do. They are too afraid of being wrong. Goodness knows there are plenty of morons ready to jump on any imperfections.

John

Just having my daily dose of snickers :-) ...Jim Thompson

We got told this morning that we are wrong most of the time in life (the sermon, at church). Guess our pastor is right. But I did get the neighbor's email back to work, hopefully that counts as the good deed of the day. :-)

A friend who's biz went belly up once told me "Yeah, it hurts. But it would have hurt more and much longer, if not forever, if I had never tried".

Hey, we had pizza from the Weber charcoal barbie yesterday. Yummy! Today it'll be steak and bread from the same barbie. Maybe beans, too.

Someone needs to impress on JL that his suggestion to Hobbs was so gross as to be laughable. I think JL was either drunk, or missed his scheduled Lithium when he drew that.

And no amount of JL's derisive farting at me will make him any more competent.

Why haven't I seen a report back on how well JL's crap circuit worked? Well? Maybe it's because his crap doesn't work.

Brain farting ain't brainstorming :-)

Can _anyone_ recall a circuit that JL posted that actually worked? I sure can't.

Can _anyone_ recall a circuit that I posted that actually worked? Sure you can, if you're honest, and not a JL sycophant. There are literally hundreds posted on the SED page of my website. ...Jim Thompson

Hey, read this:

Turns out that most people, including scientists and other "experts", are usually wrong.

John

Huh? You never know what direction a "what if?" may go, contact with the ideas factory takes a willingness to make mistakes and learn from them ;)

Grant.

We love to brainstorm circuits and algorithms at work, and we do it at every opportunity. It shakes off the static friction. Sometimes good things happen, sometimes good things happen days later.

There are a few people here who are willing to play with circuits in public. You have to ignore the background noise.

John

I think the solution to the bloviator is the "sealed envelope" approach.

Any comments on whether password-protected recent versions of WinZip are crackable? ...Jim Thompson

If John annoys you why not just ignore him? Or, even better, post a better circuit.

(I redesigned and got my transistor bidirectional translator contraption to work, but it's complicated, quirky, and pokey.)

-- Cheers, James Arthur

I think this works, once you get the zener voltage right:

ftp://jjlarkin.lmi.net/Level_shift_4.jpg

John

I think the problem with all of these is the noise margin is very low? Add in a poorly specified zener voltage...

A true "floating battery simulator circuit" would not have this issue. I thought you were going to come up with one after your coffee? :)

It _can_ be done with comparators, but not with "fast" ones that lack common mode range extending to (nearly) negative rail. Thus LM/LT119 is a no go.

And no zener is required.

Hobbs first version is probably the best solution.

Shown a market, I could create a chip that would do that, at nano-second speeds. ...Jim Thompson

If that's a concern, and it could be, the zener could be replaced by a common-base NPN, base grounded, with a dual diode, BAV99 maybe, in the collector.

No, I was going to try to figure out James' circuit after I had enough coffee. But I am not responsible for anything I say before coffee, which includes now.

But it's still an interesting little problem, the battery simulator.

John

Like this...

...Jim Thompson

Hi Jim,

Judging by the "4.8V" this still has the same potential noise issue doesn't it? JTAG works over a cable, the power supplies are processor ones so can have noise spikes etc.

Well you use perfectly matched, free transistors don't you? :)

The ground is probably stable enough.

The cabling certainly presents issues. And Hobbs was unclear on what is the definition of "fast".

But, all-in-all, Hobbs' "analog" approach was probably the best solution. You could probably embellish it with an adaptive "zener" that tracked the power supplies, but why bother.

Yep ;-) ...Jim Thompson

What about the "floating battery" idea? Is there some equivalent "virtual battery" circuit?