probe slip

John Larkin wrote in news: snipped-for-privacy@4ax.com:

You're so big on pictures. Show us a plated needle that you dremeled the chrome off with.

First explain how millions of needles all get individually chrome plated.

You do know how electroplating works, right?

Needles are highly polished steel. Some have gold electroplated ends. Some get dipped into molten glass to get beads attached to them.

They ain't car bumpers.

I don't know how they're made. But I observe that it would be easy to toss a pile onto a small metal electrode for connection.

cadence.org:

Ever heard of barrel plating? I don't know what current sewing needles are made of, and if they are plated or not, but little parts have been electroplated for many decades without attaching a separate wire to each one. Fill a wire mesh barrel half full or less, connect the cathode wire to the barrel, dunk it in the electroplating solution, start rotating the barrel like a dryer drum so the parts are constantly tumbling, and turn on the current. The tumbling stirs the solution and constantly moves the points of electrical contact between each part and its neighbors for uniform coverage. Yes, the barrel gets plated too but if the metal is valuable it can just be anodically stripped off and recovered.

snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@googlegroups.com:

The entire tangency line of which would NOT get plated. Not so easy. Sheesh.

Lasse Langwadt Christensen wrote in news:ae057b0b- snipped-for-privacy@googlegroups.com:

That idiot took clips from the actual "how it's made" video and made guesses.

That was not an el plating machine, it was an abrasive powder POLISHING machine.

They get rubbed in that for a couple days.

I saw no el plating bath anywhere.

Maybe you should watch the entire, original video.

I ordered an assortment of needles from Amazon. So I'll try it next week.

Probably a barrel plater. That's how people do connector pins. We've used barrel plating on masses of small custom screw-machine parts.

google barrel plater

Usually probing really fast logic on a PC board. The Eclips Lite gates and flops have rise times around 120 ps, and some really fast gates get down around 40. We have an eval board on some Hittite parts that are around 10, which is too fast for a home-made probe, or any probe.

I sometimes do fast high-voltage stuff too. That's really hard to measure so we make our own probes or pickoffs for them too.

I recently designed an active pickoff into a 1200 volt pulse generator; I posted about that here I think. That took three PCB iterations to get really good. The third pass was an active circuit; the passives had too much ground loops and parasitics to look good.

That's why I want to design and sell active probes. It's hard, so one can charge a lot.

I have a design for a disposable multi-GHz differential probe that I mean to try some day when we get slow. Sort of like selling razor blades.

Cool. I'll get some. Thanks.

...

Just ordered a pair from Amazon Prime.

Right. So the main reason is when you're dealing with very fast, relatively high-z signals?

cadence.org:

you might want to watch it again, it's right there. They are washed with so ap and water to remove the polishing compound and prepare them for electro plating, then a great big plating machine and a the needle comes out nice a nd shiny with the commentary that the electroplating give the needles a corrosion re sistant outer skin ..

Actually, there are no really fast high-z signals. The universe doesn't allow that. So a 1K probe impedance is usually good enough, with a DC block if needed.

OK, so what's the deal about using a FET as the active device in these kind of probes? And which particular FET gives the best results in this application?

I used blunt-tipped Pogo pins to parallel-charge 50(?) battery backs. But it's the sharp-tipped ones that make great probes.

P O G O P I N

.--------------------------. | .----------------------. |(OOOOOoO)| > | \ '----------------------' \ '-----\--------------------' pointy tip \ casing spring

A first run through the Dungeon(tm) didn't find 'em, but I know they're hiding there somewhere.

Sharp and springy is a winning combination.

Cheers, James Arthur

Passive probes have to load the signal really hard to drive the cable to the scope. The skinny flexy cables are very lossy at even low frequencies like 50 or 100 MHz, so to get flat response the source must be loaded. You can have fairly hi-z signals at 50 or 100 MHz, and that's where a fet probe really helps.

Passive probes also dump a lot of signal current into their ground clip, which is another set of problems. A good fet or sampling probe can usefully be used to snoop fast signals without a ground clip at all. Sometimes you can learn what you want to know just by putting the probe near a signal, or touching a solder-masked trace.

I don't know what fets are used in probes. I think mosfets and jfets have been used. I suspect the high-end probes are custom ICs.

Really fast signals are usually low impedance so can generally be probed with a 500 ohm or 1K resistive probe. Not always.

I find these really useful. Others seem to, also, since they evaporate rather quickly.

Cursitor Doom wrote in news:q7qtmr$v0c$ snipped-for-privacy@dont-email.me:

It is all about the slew rate. Response time.

You want to see the signal signature without distortion.

A slow probe actually dampens a bit. A fast probe allows more precise observations of shorter duration events.