litchralee

A few months ago, I was gifted a non-operational DEC VT320 serial terminal. This is a 80s/90s text-only CRT monitor, which was only displaying a thin vertical line rather than a proper picture. I've done some electronics repair in the past, but nothing this old or involving a high-voltage tube. But I figure that it would make for an interesting project over the summer, whether or not I can recover it. If nothing else, it is quite a retro talking piece.

Fortunately, DEC -- aka Digital Equipment Corporation-- made a lot of these things, and also published troves of service information, which was the norm back then (#RightToRepair). Among the documents that can be found online included the schematics, which would be of incredible aid. That said, the quality of the scan is pretty poor, and it took quite a bit of cross-referencing of component identifiers with the parts list to confirm what couldn't be read.

Before opening up the monitor, I did some preparatory research, to identify areas which would be worthwhile to investigate, and also to make sure I'm not going to shock myself in the process. My findings showed that because the CRT was able to display something beyond a single dot in the center of the screen, the issue would not be in the high-voltage generation circuitry, but rather the downstream circuits. Specifically, in the horizontal deflector path; this explains why the only image is a vertical line, because horizontal control was lost.

Using the field replacement guide, I got the monitor open and then discharged the anode using a screwdriver attached to the ground strap. There was no spark or sound, which can happen if the bleeder resistor was still intact. A good sign as to what's probably still working in this monitor, but I take no unnecessary risks around potentially high voltage.

The innards were reasonably laid out, basically existing as components that adorn the CRT display itself. The PSU, main board, and "arc protection" board were all easy to identify, although the latter was more like a connector than a board. I quickly ruled out the PSU by checking its output voltages, so the issue must be on the main board.

It took a while to extract the board, since I didn't want to break any of the 40-year old plastic clips. But once out, I began matching the board to the diagrams and examining for any obvious damage. No obviously blown caps, no evidence of thermal events, no components rolling around on the bottom.

At this point, I stopped to do some very thorough circuit analysis of the circuit diagrams, to absolutely understand what I was going to do. This actually took two tries, since each attempt revealed faults in my understanding, and I had to go back to the thinking chair. This part took a few days, until I finally internalized the circuit's behavior. As it turns out, this wasn't necessary, and I'll probably include it as a later comment, just for posterity.

When I returned to the board, I made a plan to solder some trace wires, to verify my expectations when powered on. And indeed, after reinstalling the board, my oscilloscope confirmed that the H sync signal was intact and the power transistor was functioning as expected.

Narrowing the search, I took the board back out and started tracing the lines on the PCB surface -- it was fortunately only a two-sided board -- and then compared my observations to the schematics. This revealed a difference, where the Horizontal Linearity inductor (H-LIN) was not showing connectivity, despite visibly being attached to the trace.

Closer examination revealed that of the inductor's three legs -- two for electrical connections, one extra for support -- one had developed a hairline fault. This physical damage broke continuity, likely from the shock of impacting something. I made a repair by constructing a wooden splint for physical support, and then soldered over the leg for electrical connectivity.

For good measure, I completed the exercise of verifying all other components, which showed that all other resistors, capacitors, and connectors were intact and likely working. And with that, I reassembled and powered on the monitor to see.

And it works! In total, I probably spent a week on-and-off working on this. I will say that this is a strange machine to have, since I've been able to hook it up to a modern Linux machine and use it as a serial TTY. I even wrote most of the text of this post in vim.

I only learned about this effort today. They seem to document the air protocol and the companion protocol, so that compatible implementations can be written to expand the universe of MeshCore nodes.

I'm not sure I agree with using ZephCore (a port of MeshCore to Zephyr RTOS, apparently initially AI-generated using Claude) as the reference material -- as opposed to directly referencing the MeshCore mainline repo. But nevertheless, it's a good start to formalizing the protocol behavior necessary for an interoperable implementation to those existing nodes in the field.

The convention in the USA for old urban centers and new suburban sprawl is to construct a street or road with a crown that drains rainwater to gutters along both sides of the road, then have storm drains to convey the water from the gutter to some nearby creek or tributary. But why?

Wouldn't it be easier to construct the road in a roughly canal shape, so that rainwater drains towards a single V-shaped gutter at the road's center? This would cut the number of storm drains by roughly half, prevent leaves from falling directly into a drain and clogging it, make it possible to clear a drain by driving a streetsweeper over it, and also prevent a clog from flooding adjacent properties, since the road itself can temporarily impound more water until municipal authorities can clear the blockage (whereas side gutters would invariably flood the sidewalk and carry sharp debris that would damage tires entering a driveway).

Furthermore, a center drain can be built once and then retained as-is each time a suburban arterial needs expanding -- "just one more lane, bro" -- whereas side gutters are regularly demolished and rebuilt to accommodate additional lanes. By routing water away from the edges of the road, sidewalks avoid freeze/thaw cycles, and the road surfacing can be continuous from the curb: no more bike lanes in the gutter. As a convenient benefit, the "drop" off at a curb-cut from a driveway to street level would cease to exist.

And where required to improve water quality due to runoff pollution, a center drain can be excavated and rebuilt as a linear stormwater retention pond, where moderate stormwater can filter into the local soil slowly, with a predefined overflow level that will drain to the existing stormdrain pipes. This is already done for both surface parking lots as well as Interstate highways, so it's not an unproven design.

Narrow alleyways in older cities do use a central drain, so I can't see why the idea stops making sense for larger streets and roads. The only drawbacks I can envision are aesthetic -- a neighbor's excessive lawn irrigation would draw a wet line across half the street -- and that the center channel would also carry leaves and wayward soccer balls into the middle.

But even still, that doesn't seem worse than the status quo: gutters attract all sorts of detritus, but it's usually hidden beneath the wheels of parked cars until something punctures a tire. And at least in water-starved California, irrigation runoff deserves to be noticed and called out so that it gets fixed. There may even be some small road safety benefit from having a V-shape channel in the center, since it would unmistakably divide opposite sides of the street.

For larger arterial roads that have trees in the center, this seems like free irrigation and water pollution control. It even works when the center traffic lanes are converted for running a tram or light rail train.

What am I missing here?

cross-posted from: https://sh.itjust.works/post/61250326

A crafted MeshCore node name could compromise any Home Assistant instance running meshcore-card as soon as someone viewed a dashboard with that card.

The same XSS (cross-site scripting) pattern appears to be present in MeshCore-Home-Assistant-Panel-v2 and its HACS variant

To be abundantly clear, and the post goes into detail why, this is not a bug in MeshCore but rather in how web dashboards are not properly sanitizing untrusted input. In this case, the untrusted input is via a field that any malicious MeshCore node could send.

Well worth a read and a follow on their Mastodon.

A crafted MeshCore node name could compromise any Home Assistant instance running meshcore-card as soon as someone viewed a dashboard with that card.

The same XSS (cross-site scripting) pattern appears to be present in MeshCore-Home-Assistant-Panel-v2 and its HACS variant

To be abundantly clear, and the post goes into detail why, this is not a bug in MeshCore but rather in how web dashboards are not properly sanitizing untrusted input. In this case, the untrusted input is via a field that any malicious MeshCore node could send.

Well worth a read and a follow on their Mastodon.

A reasonable overview of the MeshCore architecture and tunable parameters.

Probably the only part I don't agree with is the idea that the companion/repeater dichotomy is an inherent part of the MeshCore architecture. I don't believe it is, although it's certainly part of the practical implementation. That is to say, if someone wants to use MeshCore purely as a private point-to-point link, then they can jettison the motions of companions and repeaters entirely. As a person to person mesh network, though, companions and repeaters are essential. The distinction I'm trying to draw is that MeshCore can be a lot more than text messages sent amongst friends.

While reading, the explainer for the three-tier t delay seemed especially analogous to me to how circuit breakers are arranged: a nearby power strip might have a fast-tripping 15 amp thermomagnetic breaker, the upstream main panel might be using a 20 amp curve B (moderate trip rate) thermomagneric breaker, and the utility might be using a magnetic 400 amp breaker. By their nature, thermomagneric breakers will handle localized faults that are 3-5x the rating, while the utility's magnetic breaker will trip precisely at 400.1 amps, to protect line-side equipment. Whereas if the utility breaker tripped first, it would unnecessarily black out a whole neighborhood.

Also observe that MeshCore's "flood-then-direct" behavior is identical to that of Ethernet (ie unknown unicast, then unicast), except that Ethernet frames do not get appended with the network path as they progress, which is akin to the postal service where letters arrive at their destination but with no indication of the routing. Accordingly, the MeshCore sender necessarily reserves space to store the mesh route, choosing a tradeoff between node-count (up to 64) or granularity (up to 3 bytes per repeater). This seems complex, but just like with the tax code, complexity is necessary to handle every reasonable scenario.

I will also reiterate the ongoing bug in MeshCore's encryption, which is the use of AES-ECB in the year 2026. Although it's AES-256, ECB has been a known encryption vulnerability for decades and should not have been used in the MeshCore spec. Meshtastic appears to have avoided this particular foible.

Note: the author's blog mentions in the About page that some AI is used to assist in his writing.

Background: I spent 40 minutes typing up a reply to a different post, but decided that it ran on for too long. I'll include it at the bottom, but I'm curious to know how much cash is still used in this country.

Certainly, a like-for-like Giro (Europe) system doesn't exist in the USA, with ACH, checks, and Zelle almost filling the void -- albeit incompletely -- which I suspect is responsible for the remaining cash utilization. But is that right? Is cash only used for when there isn't another option? Or is it a matter of consumer preference?

I can understand tipping in cash, or paying for a Craigslist purchase in cash. But maybe I'm missing another dimension? Do some folks pay rent in cash? Or taxes? I'm genuinely curious, but please make sure not to dox your finances in the comments.

What can be done

The most glaring problem with MeshCore is that the maintainers do not openly communicate vulnerabilities. Users are left without knowledge of any problems, unable to judge whether to trust MeshCore with their private communication.

Here is the thing about open source, Andy: it isn't yours to fence. You don't get to ride a community's goodwill into a USPTO filing and a paywall. You don't get to turn "we built this together" into "I own this, pay me." That isn't a pivot. That's a rug pull dressed up as a business model.

And here is the thing about the "license check" you shipped: it is a 32-bit djb2 hash of the device's Android ID, XORed with the four ASCII bytes MCPP, hex-encoded. That's it. Thirty-two bits. Less entropy than a decent ZIP password. A first-year CS student could break it. You used Claude to generate the code. We used Claude to read the code. It took 19 minutes. The receipts are one click away.

CLAUDE CODE JUST RICKROLLED ME. I'm working on a project where part of it will involve videos, and in building out the project it created a dummy page, with made up content (relevant to me!) with two video links pretending to be something else and BOTH WERE RICKROLLs.

Note: I'm using a broad definition of "programmer" to include HTML generation, and a broad definition of "humor" that includes Rickrolling. Together, I think this is appropriate for c/programmerhumor. Mods, please remove if not correct.

The money quote:

VTA buses and light rail carried 30,000 people to and from Levi's Stadium, according to the agency. That was 5,000 more than they anticipated and "far surpassing" ridership records set when Taylor Swift played there in 2023.

As background from the Wikipedia page, the Anaheim Transit Network (ATN) was established as a city-sponsored non-profit in 1998 to operate bus lines around the Disneyland resort in California, with private funding from the various hotels in the area to run this public bus system. These hotels are obliged to operate or pay for shuttles to Disneyland as part of their development agreements with the city, presumably to avoid untold amounts of automobile traffic.

As the linked press release says, ATN will shutter its operations on 31 March 2026. The area will still be served by Orange County Transportation Authority (OCTA), the county-wide bus service, but looking at the bus lines near Disneyland, coverage seems non-optimal as a replacement to ATN's service.

Other reporting indicates that the City of Anaheim was unwilling to invest further into ATN (despite earlier indications), nor were the hotel operators.

What I find utterly inexplicable is that these stakeholders -- especially the city -- are not recognizing this fact: data from Q3 2025 shows that ATN fixed-buses moved 96,300 average daily riders. From the same document, the USA's heavy rail systems did not exceed that rate, except in the San Francisco, Washington DC, Atlanta, Chicago, Boston, and NY/NJ areas. Basically, ATN was moving metro rail levels of people on buses.

I shudder to imagine how bad this will be for Anaheim once the closure occurs, where workers, visitors, and all other former riders will need to figure out how to move around Anaheim. Ride share automobiles hardly have enough capacity to absorb even a fraction of the prior riders, let alone more automobiles, even if they all carpooled. And seeing as many visitors to Disneyland use the buses to stay at farther hotels to reduce costs, this is a negative attraction. The difficulty of car-seats on ride share made the buses particularly attractive to transport younger children safely.

Each individual hotel operator made an economic choice to not properly fund ATN, but together they will all lose out. Likewise, I don't see how the City of Anaheim is going to make up the transportation capacity around the Disneyland area. Disneyland itself isn't party to the agreement that funds ATN, but they do contract with ATN to shuttle visitors from a far-flung parking lot. But they too will be impacted if staff and guests can't afford to get to the park.

Everyone is going to be worse off, and no one is stepping up to the plate to keep the buses rolling, when it's clearly the obvious thing to do.