Archive for the ‘Miscellaneous’ Category

What Shape Portable USB Powerbank?

Thursday, November 4th, 2021

Cort and I would like to embed lithium cells in portable projects and want power management that:

  1. steps up the lithium cell’s 3.7 V to a well-regulated 5 V
  2. safely charges the lithium cell from some source
  3. powers the load while charging the cell

I knew it’d be easy finding power management modules that met the first two points, but I wasn’t sure whether the third point (power the load while charging) would be a ubiquitous feature, or even clearly called out in documentation. Fortunately, while browsing power management modules, I quickly found that the HT4928S mobile power management chip supports all three, and found cheap modules both with and without USB connectors on them, and ordered a batch of each style.

18650 lithium cell with power management modules

Now I have them and need to test that they work as described, preferably without burning down my house or pocket. The obvious test is to hook one to a secondhand 18650 cell I have lying around. While I’m at it, I may as well 3D-print an enclosure for it and have a spare USB powerbank.


The Lawn Under the Lawn

Sunday, August 22nd, 2021

“Yak shaving,” well-known among a certain class of nerds, refers to artificial dependencies that you insert before your ultimate objective, distracting you and derailing you from getting the job done. My favorite sample yak shaving is on Seth Goden’s blog from 2005.

Yak shaving would be: I want to use the lab power supply on my workbench, but my CupCake is hooked up to it, and I haven’t finished getting the CupCake’s aging extruder motor to work, so suddenly I’m spending the weekend working on the CupCake, so I can get it fixed and move it out of the way, so I can use the power supply under it to do … whatever it is that I was going to do. (This is a fictional, but relatable, example.)

Some time back, Cort said to me:

Doing technology work is often like going out to mow your lawn, and you think it’s going okay, but partway into it you discover there’s a whole ‘nother lawn under your lawn, and now you have to mow the one underneath before you can mow the one you thought you were there for. And then sometimes you start mowing the lawn under your lawn and you find out there’s another one under that, too.


I’m Not Dead Yet

Monday, June 18th, 2018

I see I haven’t posted for three years. Well.

I started this blog to share what I was working on with a handful of close friends, rather than email the same thing to each. I don’t recall that commercial blog hosting was prevalent at the time like it is now; I was at a different place in my career and finances were tighter; and I already had my own domain and ran my own server; so I just set up WordPress at home. In the basement. On my DSL connection. Where it still is.

The WordPress software uploaded the fact that I was blogging and I started getting picked up by Google. I did a few projects of interest and got a few more readers than I expected.

For a while, I had a generous arrangement to host my image files elsewhere, offloading that bandwidth from my home broadband; but that came to an end a while back. The combination of increased bandwidth requirements (making ultra-slow load times) and an increasingly busy schedule has meant no posting for quite a while.

I’ve been looking into migrating the blog to commercial hosting and Ed Nisley has generously shared information about his hosting service and their capabilities, which sounds like just what I need. I’m hoping to get that migration underway sometime soon … which might mean inside the next three years.

Meanwhile, maybe I’ll do some posting again. Images will be horribly slow to load; but anyone who wants to read can read and anyone who doesn’t is under no obligation.


Filimin — Back My Friend John’s Kickstarter!

Tuesday, May 5th, 2015

Filimin is a lamp that turns colors when you touch it and uses a cloud service to synchronize colors with its “group” of lamps anywhere in the world that has WiFi. John Harrison invented it last Christmas as a way for his family to maintain emotional contact across the continent and beyond — touch the lamp and it lights up in a new color to let your family see that you’re thinking of them before it eventually fades to black again.

I’ve already backed the project but it’s only 30% of the way to its $50,000 goal with 15 days to go. If it sounds interesting to you, too, please check it out, back the project, and help ensure that I end up getting my set. :-)

Finding a Picture That I Took Used on eBay

Sunday, January 6th, 2013

It is a bit surprising to follow a link from an eBay saved search and find a picture that I took.

Liebert UPS battery cable

The original is in this post from 2011.

I have no CC notices posted for the whole site (though I’d be happy to); but of course the Berne Convention provides for automatic copyright upon creation and publication of a work, so this is a blatant copyright violation.

Regardless, why is an eBay seller with only 110 feedbacks (vs one who does business on a scale of 110,000) too lazy to take their own picture of what they claim to have for sale?

72G or Larger SCSI-2 Fast/Wide Hard Drives?

Monday, November 26th, 2012

Anyone know where to find new, large-capacity SCSI-2 fast/wide hard drives? A computer I supported at a hospital a long time ago has a failing hard drive and I’m happy to assist with replacement but I’m not coming up with any sources for the hardware.

Hand-Soldering SOIC

Monday, July 2nd, 2012

I wouldn’t want to do it for a living, but it’s an enjoyable diversion once in a while, particularly as a favor for a friend.

Breakout boards with SOIC

I aligned each chip’s pins by hand, clamped it to the board with a gator clamp (with heatshrinked jaws), soldered the far row of pins, rotated the board, and soldered the now-far row of pins.

Three rows I was able to do by blob-and-drag (heat the pins at the uphill end of the row, make a big solder blob, and drag it down the row at a pace slow enough to heat the pins but fast enough to keep the surface of the blob from oxidizing too badly, trusting surface tension to bring the blob with you and leave only a lovely solder fillet below each pin). Three rows I ended up doing slop-and-wick (get solder all over the place, then use “Size: Good” solder braid to remove solder bridges from between the pins, leaving a lovely solder fillet below each pin and evidence scorched flux everywhere).

I’d take recommendations on a good flux remover — preferably detailed recommendations indicating whether you have to scrub or just spray, how cleanly it washes off, etc. You can see that the rubbing alcohol I used leaves a bit of residue.

Liebert Battery

Saturday, May 28th, 2011

Just found this unpublished draft from October. I had received a GXTV2-48V battery expansion cabinet for my Liebert GXT2-2000RT120 UPS and wanted to see what was inside.

Liebert GX2-48VBATT battery cabinet interior

Eight sealed lead-acid batteries are bolted down and connected through a circuit breaker / switch to the two input/output jacks in parallel.

Liebert GXT2-CABLE48V1 UPS battery cable

The cable to daisy-chain the battery expansion cabinets to the UPS is … substantial.


Installed in the basement server rack (bottom) and connected to the UPS. Sure wish I had a bezel for the battery cage.

Cleaned It. What Now?

Friday, January 28th, 2011

Rotary crank telephone, dirty

People bring me the most wonderful things!

Rotary crank telephone, cleaned

Anyone have a favorite plastic polish?

Old telephone handset

I suppose I should build a VoIP phone system and get an analog terminal adapter, eh?

Does Used Tinnit Ever Work?

Friday, January 21st, 2011

The board being too long for my Pyrex dish and the overlap in the middle notwithstanding, this dull, mottled finish is typical of what I get every time I use TInnit other than the day I mix it.

PC board after tinning in used Tinnit

The precipitate never re-dissolves; and I’m guessing that the salts sitting directly on the board are what cause the mottling.

I find this curious, as I mixed this batch only two weeks ago, when it worked noticeably better than this … although now that I mention it, I think even then it produced duller results than it has in the past. Perhaps I exceeded the shelf life of the unopened package, so perhaps I’m being unduly hard on the Tinnit; but I’ve had the same problem before.

PC board after tinning in Tinnit and wet-sanding

I’ve been having good luck lately with scouring pads to shine up the boards; but tonight I had to resort to wet-sanding. Turned out fairly well.

No, that’s not how I typically lay out circuit boards.

Yes, I’ll be posting a lot more about what I’ve been doing for the last month as soon as Steve and I get his sculpture delivered to the gallery before 17:00 tomorrow.