testing the TI switchers

I added SMB coax connectors to the outputs. It's hard to measure

Yup. We sprinkle U.FL footprints on our boards for the same reason. They're cheap and small, and make probing a breeze.

We use Aliexpress connectors and stuff in POCs and suchlike. Since Hammond and Bud jacked up the prices on their extruded cases, we're going to Aliexpress extrusions plus laser-cut end plates from SendCutSend.

Cheers

Phil Hobbs

We did our own extrusions to replace the dreadful Hammond stuff.

We laser them to do the artwork. We thought we were removing the anodize, but I think we're just removing the dye. It's still non-conductive.

We do need to be careful that everything is solidly grounded. Undercut flathead screws cut into anodized countersinks pretty well.

Tek offers a TPR1000/4000 to help you out. :)

Olaf

You might consider using Noalox on the joint:

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Joe Gwinn

They make a reliable ground if you use these washers

making a gas-tight contact. For power safety ground, of course, you want a connection OTHER than a fastener that can be loosened from outside the box (like, a rivet, or externally-unreachable screwdown).

I could get some to try, but I think they would look klunky on an external end plate. People already are whining about the undercut flatheads, which extend maybe 20 mils above the panel.

These little boxes are powered from warts and usually bolted down, so we don't need a big ground lug.

Yes, it was a real find. In my circuit, it trips when the +1v switcher hits +0.5, and then it sequences the rest every 30 ms. The Zynq FPGA wants to be, possibly needs to be, supply sequenced. The SRST# output un-resets everything and starts the boot process.

I'd prefer a slower version, but the 30 ms one was available.

R103 discharges the +1 rail during brownouts, to make sure the sequencer runs when power returns. U15 guarantees a minimum brownout time to let stuff discharge. Ideally no brownout or fumbling with a wall-wart can hang the system up.

There's still the ground clip. A coax gives a really solid ground from the board to the scope, or to a preamp to see the tiny stuff.

With probes, you run out of hands too. SMB connectors are handy on important things like clocks, so you can poke other things with probes.

So you're using a thin head that's flat top and bottom to cut into the conical surface?

("Flat head screw" means countersunk in my lexicon, as opposed to (for example) the painted oval head things that come packaged with outlet plates from Home Depot.)

Cheers

Phil Hobbs

With a good adjustable stop, you could countersink the endplates for your choice of extension; 2 mils above, flush, two mils below...

Flat head is the correct term for the kind that goes flush in a countersunk (conical) hole. The oval things have "oval" heads.

Here is the rest of the chart:

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The bible for all such things is "Machinery's Handbook", first edition published in 1914, and continuously ever since. Current is the 31st edition.

.

There are lots of used copies available for small dollars in such as used tool stores (and eBay).

Older editions are perfectly serviceable, especially for a small shop with manual machines. I use the 27th edition, and also the 25th edition.

The original size was meant to fit into the upper center drawer of a standard machinist's 8-drawer toolbox, such as that made by Kennedy. This size is now known as a "toolbox" edition, and it's larger version is a "big-print" edition.

Joe Gwinn

Looks like a regular flathead, but undercut below.

(We're using 6-32 and metric on various boxes.)

Undercut is normally used to keep the screw from bottoming on the box and making the thin end plate get loose, but the sharp edge also cuts into the anodized countersink and makes a good ground.

A regular flathead screw in an anodized countersink can be iffy electrically. Parallel rubbing surfaces.

Ahh. I wondered what exactly was being used. It's called a "flat undercut" head.

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I'd put a drop of Noalox on the screw before installation, covering both the threaded part and the underside of the screw head.

Noalox will also act as an anti-seize compound.

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Available at Lowes, Home Depot, et al.

Joe Gwinn

My mistake for calling it "undercut flathead" instead of "flathead undercut."

Some of this is clean-room gear. Zinc particles might not be welcome.

Hm - yes, nice, but at a price where I can get a small microcontroller which will do other tasks at the same time.

cu Michael

A microcontroller has to be programmed, which has its own costs. And it still needs guaranteed clean powerup and powerdown and a regulator down from the 12/24 volt prime supply.

We have a 400-ball Zynq do do any computing that we need.

A reel of LM3880's cost us 44 cents each, not even rounding error on product price.

Yes; I was citing the standard term, versus a description. In this case, both terms would work for google, but that is often not the case.

For clean rooms, probably not. What fraction of the users would this be?

If necessary, there is a trick. After seating the zinc particles in the aluminum with a screw used only for that (or a conical tool pressed from above), wash the alnox off with solvent and assemble using a clean screw. The zinc particles should largely be trapped in the aluminum. I don't know if this is good enough for those clean rooms.

Joe Gwinn

In the tool core rather than the fab side of the wall, right?

Cheers

Phil Hobbs

This particular box is used in the sub-fab, the light source a floor below the wafer fab, and in the wafer area itself.

We have an elaborate ritual where we clean each box in a laminar flow hood and triple-bag each one.

The old Hammond boxes used self-tapping screws and liked to strew metal shavings, which usually stayed inside the boxes.

The LM3880 also needs a regulated 5V supply. Programming is done by the distributor before assembly (yes, that costs some additional cents).

I was quoted similar prices for STM32G030 back before they went unobtainium ... we now use GD32. The microcontroller does system management including temperature and fan control, and protects the main CPU even if it locks up hard and overheats.

cu Michael