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Posts Tagged Memo to Self

Fake Flash

This 2 GB flash drive arrived with datasheets & sample files for a (computerized) sewing machine Mary eventually decided she wasn’t going to get (because computerized):

Fake Flash drive

Fake Flash drive

Being of sound mind, we reformatted it and dropped it in the bag o’ random drives. She eventually used it for one of her gardening presentations, whereupon the library’s (Windows) laptop said it needed formatting; she pulled out a backup drive and continued the mission.

Lather, rinse, verify a good format, verify presentation files on the Token Windows Box, and repeat, right down to having another library’s laptop kvetch about the drive.

Soooo, I did what I should have done in the first place:

sudo f3probe -t /dev/sdc
F3 probe 6.0
Copyright (C) 2010 Digirati Internet LTDA.
This is free software; see the source for copying conditions.

WARNING: Probing normally takes from a few seconds to 15 minutes, but
         it can take longer. Please be patient.

Probe finished, recovering blocks... Done

Bad news: The device `/dev/sdc' is a counterfeit of type limbo

You can "fix" this device using the following command:
f3fix --last-sec=25154 /dev/sdc

Device geometry:
	         *Usable* size: 12.28 MB (25155 blocks)
	        Announced size: 1.86 GB (3893248 blocks)
	                Module: 2.00 GB (2^31 Bytes)
	Approximate cache size: 511.00 MB (1046528 blocks), need-reset=no
	   Physical block size: 512.00 Byte (2^9 Bytes)

Probe time: 55'18"
 Operation: total time / count = avg time
      Read: 8'35" / 3145715 = 163us
     Write: 46'37" / 18838872 = 148us
     Reset: 350.7ms / 2 = 175.3ms

Huh.

As long as you don’t write more than a few megabytes, it’s all good, which was apparently enough for its original use.

The front of the PCB looks normal:

Fake Flash - controller

Fake Flash – controller

But it seems they really didn’t want you to see the flash chip:

Fake Flash - covered chip

Fake Flash – covered chip

Given the two rows of unused pads, it must be a really small chip!

Memo to Self: Always examine the dentition of any Equus ferus received as a gift.

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Baofeng BL-5 Battery Pack: Recharge and Reassembly

Separately charging all four cells from the Baofeng BL-5 packs covered the Electronics Bench with wires:

Baofeng BL-5 cell charging

Baofeng BL-5 cell charging

The cell sits on a ceramic tile as a nod to fire safety, although I doubt it makes any difference.

The discharge tests showed two nearly identical pairs:

Baofeng BL-5 Cells - Separate Charge - 2018-02-24

Baofeng BL-5 Cells – Separate Charge – 2018-02-24

Surprisingly, cells A and B (upper traces) were deaders in the original packs. Cells C and D (lower traces) were more-or-less fully charged, but now have a lower terminal voltage and slightly lower capacity. I have no explanation for that, nor for the voltage undulations.

The rebuilt packs pair up A+B and C+D.

Reassembling pairs into the pack shell and resoldering all the leads produces a good pack:

Baofeng BL-5 battery rebuild

Baofeng BL-5 battery rebuild

I later added a snippet of heavy manila paper under the nickel tape bent around the edge of the pack as a third level of insulation, in the interest of having the nickel tape not produce a dead short between the isolated – terminal and the + cell case.

Memo to Self: tape the long wiggly leads from the protection PCB to the radio contacts (at the left side) before soldering the PCB to the cell terminals, because an inadvertent short will convert the 8205A battery protection IC into a Light-Emitting IC, at least for a moment, and subsequently release the Acrid Smell of Electrical Death. A handful of charge PCBs are en route halfway around the planet, from which I intend to liberate one IC for this board; with luck, I didn’t incinerate anything else.

The pack works fine in the radio, as does the APRS interface:

APRS Coverage in Poughkeepsie - 2018-03-01

APRS Coverage in Poughkeepsie – 2018-03-01

Unfortunately, two APRS iGates vanished in the last year, leaving poor coverage south of Poughkeepsie.

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Pogo Pins

A Pogo Pin reference may be useful:

  • P.. and R.. refer to Pin and Receptacle (a.k.a. socket), respectively
  • Pxx  and Rxx = nominal pin diameter in 0.01 mm units: P50 = 0.48 mm

For pins, the suffix -hn indicates pin head shape, the most useful of which may be:

  • B1: 45° cone
  • J1: dome end
  • Dx: large dome, also 1D
  • Gx: cylinder
  • Ex: large 90° cone, sometimes 1E
  • T2 – large chisel

For sockets, the suffix -ntl gives:

  • n – entry shape: 1 = shaped entry, 2 = straight entry
  • t – termination: C = crimp, S = solder, W = wire
  • l – length of wire in 100 mm units: 7 = 700 mm

From what I can find on eBay, all pins have 6 mm travel with typically 75 / 100 / 180 g spring force.

A picture ripped from the reference to forestall link rot:

P75 Spring Test Probes

P75 Spring Test Probes

Memo to Self: US-based eBay sellers charge three times more than Chinese sellers, but deliver in one-third the time.

[Update: Simon sends a link to Everett Charles Technologies, a pogo-pin manufacturer providing “Probably much more information than anyone should ever want”. Of course, eBay / Amazon junk may not meet any particular specs, so scale your expectations accordingly.]

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Scrap Metal Prices

Earlier this year, I finally hauled a pile o’ scrap metal to the recycler. For future reference, here’s what clattered down on the scale:

Scrap Metal Prices - 2017-04

Scrap Metal Prices – 2017-04

I think the IRONY tag means ferrous bits & pieces in the mix. There’s a powerful motivation to hand them clean copper scrap, although I stop just after cutting off soldered pipe fittings and before stripping insulation.

Memo to Self: Next time, ask about PCBs and gold-plated connectors.

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Fordham FG-801 Function Generator Power Switch

The power switch in my trusty Fordham FG-801 Function Generator failed with an accumulation of oxidation / crud on the contacts. That’s fix-able, but the switch contained not one, but two powerful springs, and puked its guts all over the floor around the Squidwrench Operating Table. Even with (a preponderance of) the parts in hand, I couldn’t figure out how to reassemble the thing; the only way out was to replace the switch.

The OEM switch had a 0.360+ inch diameter pushbutton that fit into a ⅜ inch hole and, alas, my remaining stock of line-voltage switches had toggle levers and used ¼ inch holes. So I converted a bit of aluminum rod into a suitable bushing:

Fordham FG-801 Fn Gen - new switch hardware

Fordham FG-801 Fn Gen – new switch hardware

The lock washer in the middle started with a much wider tab that I filed down into a tooth for the dent from a #2 center drill. Protip: center drills don’t walk off like twist drills, even when you hand-hold the front panel at the drill press with all the electronics dangling below.

The bushing dimension doodle:

Fordham FG-801 Function Generator - Replacement Switch Bushing

Fordham FG-801 Function Generator – Replacement Switch Bushing

The internal wiring routes the 120 VAC line conductor to the switch, then to the fuse, then to the transformer. I don’t know whether it’s better to have an unfused switch or an unswitched fuse (surely there’s a UL spec for that), but I didn’t change anything. The new switch, being slightly smaller and mounting directly on the panel, required a new wire (the blue one) from the fuse:

Fordham FG-801 Fn Gen - power switch - installed

Fordham FG-801 Fn Gen – power switch – installed

The OEM switch mounted on two round brass standoffs and, wonder to tell, the new switch fit between them!

From the front, the new switch looks like it grew there:

Fordham FG-801 Fn Gen - switch in action

Fordham FG-801 Fn Gen – switch in action

The PCB mounts to the top of the case with one screw and four hexagonal brass standoffs. The standoffs have 6-32 tapped holes on one end and a 6-32 stud on the other; one of those stud had broken off. A 6-32 stainless steel screw secured in a clearance hole with a dab of epoxy solved that problem:

Fordham FG-801 Fn Gen - standoff stud

Fordham FG-801 Fn Gen – standoff stud

I stood it vertically and tweaked the screw to be perpendicular while the epoxy cured.

Memo to Self: The next time around, put a nut on the stud to make sure the answer comes out right. I didn’t do this time to avoid epoxying the nut to the standoff.

Done!

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Raspberry Pi: Forcing VNC Display Resolution

You can use VNC with a headless Raspberry Pi, but, absent a display with which to negotiate the screen resolution, X defaults something uselessly small: 720×480. To force a more reasonable resolution, edit /boot/config.txt and set the framebuffer size:

framebuffer_width=1920
framebuffer_height=1280

You can use a nonstandard resolutions, as with the 1920×1280 that fits neatly on my 2560×1440 landscape monitor, but getting too weird will surely bring its own reward. When you plug in a display, X will ought to negotiate as usual for the highest resolution the display can handle.

The System Configuration dialog has a “Resolution” button offering standard resolutions:

RPi display resolution configuration

RPi display resolution configuration

The shiny RPi Pixel UI bakes the RealVNC server directly into whatever handles the startup process these days, rendering all previous recommendations about forcing VNC resolutions inoperative. I found the trick of editing the config file on StackExchange after the usual flailing around.

Memo to Self: Remmina (the VNC client I use in XFCE on my desktop PC) doesn’t respond well to having the VNC server shut down while it’s connected. Fire up a command prompt, enter this:

sleep 10 ; sudo reboot

Then, quick like a bunny, disconnect the VNC session.

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Blog Backup

Recent news about Dropbox removing its Public folder feature reminded me to do my every-other-month blog backup. Wordpress provides a method to “export” the blog’s text and metadata in their XML-ish format, so you can (presumably) import your blog into another WordPress instance on the server of your choice. However, the XML file (actually, ten of ’em, all tucked into a paltry 8 MB ZIP file) does not include the media files referenced in the posts, which makes sense.

Now, being that type of guy, I have the original media files (mostly pictures) tucked away in a wide variety of directories on the file server. The problem is that there’s no easy way to match the original file to the WordPress instance; I do not want to produce a table by hand.

Fortunately, the entry for each blog post labels the URL of each media file with a distinct XML tag:

		<wp:attachment_url>https://softsolder.files.wordpress.com/2008/12/cimg2785-blender-bearings.jpg</wp:attachment_url>

Note the two leading tabs: it’s prettyprinted XML. (Also, should you see escaped characters instead of < and >, then WordPress has chewed on the source code again.)

While I could gimmick up a script (likely in Python) to process those files, this is simple enough to succumb to a Bash-style BFH:

grep attachment_url *xml > attach.txt
sed 's/^.*http/http/' attach.txt | sed 's/<\/wp.*//' > download.txt
wget --no-verbose --wait=5 --random-wait --force-directories --directory-prefix=/where/I/put/WordPress/Backups/Media/ -i download.txt

That fetches 6747 media files = 1.3 GB, tucks them into directories corresponding to their WordPress layout, and maintains their original file dates. I rate-limited the download to an average of 5 s/file in the hope of not being banned as a pest, so the whole backup takes the better part of ten hours.

So I wind up blowing an extra gig of disk space on a neatly arranged set of media files that can (presumably) be readily restored to another WordPress instance, should the occasion arise.

Memo to Self: investigate applying the -r option to the base URL, with the -N option to make it incremental, for future updates.

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