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Data Engineering

Death by a Thousand €3s: the EU import tax that’s pushing me off AliExpress

by Marc 10 June 2026
written by Marc

Ten years of cheap electronics, and a new €3 charge that quietly makes the whole habit pointless.

I’ve been buying from AliExpress since November 2015. My first order, for the record, was a €1 bag of replacement screws for a MacBook — the sort of thing no shop near me stocks and no sane person pays shipping for. That pretty much set the tone for the next decade.

I pulled my whole account history the other day and counted 322 orders. Just under €5,000 over ten years, which sounds like a lot until you look at what it actually was: jumper wires, GPIO headers for a Raspberry Pi, solder, a handful of sensor boards, plastic sleeves for my game cartridges, little displays you genuinely can’t buy here in the Netherlands without paying three times the price. Supplies, basically — the raw material for a hundred small weekend projects. There were a couple of real splurges buried in there too — a brand-new iPhone, the odd used MacBook SSD — but mostly it’s a long, boring list of things that cost a euro or two.

For all that it comes to ten years and nearly €5,000, the median order was about €5. Almost half of everything came in under that, fifty-odd orders were under €2, and the cheapest was a literal one cent. The most expensive single thing in a decade was that new iPhone, at €499 — the exception that proves how small the rest of it is. That’s the shape of it: a steady drip of tiny parcels, around thirty a year, with the occasional proper purchase thrown in.

On 1 July 2026 the EU changes the rules in a way that makes that kind of shopping stop adding up. So I’m winding the account down. Here’s the thinking.

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10 June 2026 0 comments
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PythonTools & Automation

Reverse-engineering a Honeywell T4R wireless thermostat with a Raspberry Pi Pico + CC1101

by Marc 4 June 2026
written by Marc

A from-scratch RAMSES-II receiver on the cheapest hardware that works — and the one detail that makes the signal look encrypted when it absolutely isn’t.


You can sniff and decode your Honeywell evohome / T-series heating straight off the air with a Raspberry Pi Pico and a ~€1 CC1101 radio — no nanoCUL, no ESP32, no pre-built firmware. Here’s the whole thing from scratch: the exact wiring, the working code, and the one detail that makes the signal look encrypted when it isn’t.

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4 June 2026 0 comments
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Data Engineering

How many jelly beans are in the jar?

by Marc 27 May 2026
written by Marc

Here is a jar of jelly beans. How many are in it?

Take a guess and hold onto it. We’ll come back to it — and to the slightly unsettling fact that nobody, including the people who set the puzzle, actually knows the answer.

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27 May 2026 0 comments
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Twelve game-cover examples in a 4x3 grid, each labelled: clean, 3d_render, deluxe_bundle, multi_platform, wrong_console, wrong_game, low_resolution, bad_background, margins, placeholder, gkc, ciab
Python

Teaching a small CNN to pick the right cover image

by Marc 22 May 2026
written by Marc

A side project of mine is a video-game price-comparison catalogue. It pulls product data from a handful of retailers — affiliate feeds, public web APIs, a couple of cookie-based scrapers — and shows you which of them currently has the best price on a given title. About 27,000 editions across ~12,000 games.

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22 May 2026 0 comments
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Three LiitoKala 34B 18650 cells stacked, showing positive terminals and flat tops
Tools & Automation

LiitoKala 34B 18650 — first impressions in a Waveshare UPS 3S

by Marc 22 May 2026
written by Marc

I picked up three LiitoKala 34B flat-top 18650s to populate the Waveshare UPS Module 3S sitting under my Raspberry Pi 5 home server. The cells are sold as a Panasonic NCR18650B rewrap — the printed cell label reads NCR18650B Li-ion. They came from the LiitoKala official store on AliExpress at about $2/cell after coupons and AliExpress coins (closer to $4 at sticker), which is well under half what genuine retail-channel Panasonic cells go for.

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22 May 2026 0 comments
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Lessons LearnedTools & Automation

The Caveat Nobody Mentions

by Marc 5 May 2026
written by Marc

I started using Claude Code in December last year. In four months, I’ve delivered what my team would have needed two or three years to ship — at least. That sounds like a happy ending. It isn’t quite.

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5 May 2026 0 comments
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Lessons Learned

Builder is the new role

by Marc 2 May 2026
written by Marc

Early 2025 AI was a toy. ChatGPT could write a function, sometimes correctly, often not. It was impressive in demos and frustrating in practice. A year later the picture is unrecognisable. AI is now genuinely useful — useful enough that I can build almost anything I want in a single day, regardless of how complex it is.

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2 May 2026 0 comments
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Lessons LearnedTools & Automation

The Productivity Multiplier Has a Tail at Infinity

by Marc 2 May 2026
written by Marc

Last year I went to the Google Cloud Summit with a few colleagues. We saw a lot of impressive projects built around agents and LLMs, and walked out a bit deflated. As a data team — analysts, engineers, but not “pure” software developers — we could see the value clearly, but we’d seen this movie before: the moment we wanted to build something real, we’d be queuing up for backend developer time, or pricing out an external consultant to implement agents for us. Same bottleneck as always, just with a fancier label.

A year later, that bottleneck has quietly dissolved. We built it all ourselves — fast — with Claude Code as the agent in our IDEs. The projects we thought we’d have to outsource, we shipped on quiet afternoons.

And it isn’t just the work-shaped projects. I’m finally shipping ideas that have sat in my personal backlog for literally ten years — the kind of thing where every time you open the notebook you remember why you closed it last time. Now they’re real, deployed, and — the part I keep being surprised by — they’re solid. Tests, sensible error handling, security defaults that hold up to scrutiny. Not vibey demos. Things I’d hand to a friend without a list of caveats.

When people ask how much faster I work with the agent, my honest answer is that “faster” is the wrong axis. I built this chart for an internal talk last week to explain why.

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2 May 2026 0 comments
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Lessons LearnedTools & Automation

Tricks and Behavioural Patterns I Taught My Coding Agent

by Marc 25 April 2026
written by Marc

I wrote three months ago about the context files and memory system behind my AI coding agent. This post is the follow-up I wish existed back then: the concrete tricks and patterns that make the agent reliably useful, not just occasionally impressive. Most of these are small. They compound.

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25 April 2026 0 comments
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BigQueryData EngineeringdbtLessons Learned

Teaching an AI Bot Your Metrics, Part 2: One Layer for Logic, One Thin Layer for Aggregation

by Marc 25 April 2026
written by Marc

In Part 1 I wrote about how our AI Slack bot was confidently wrong about revenue, and how a hand-maintained corrections file fixed it. That file grew. After three months it was six hundred lines long and still did not stop the bot from producing numbers that disagreed with the dashboards. This post is about why the corrections file could never work, and the week-long migration that finally made it unnecessary.

The short version: we already had a semantic layer. That was the problem. The bot had to reconcile business logic that lived in two places at once, and no amount of prompting was going to make it good at that.

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25 April 2026 0 comments
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Recent Posts

  • Death by a Thousand €3s: the EU import tax that’s pushing me off AliExpress
  • Reverse-engineering a Honeywell T4R wireless thermostat with a Raspberry Pi Pico + CC1101
  • How many jelly beans are in the jar?
  • Teaching a small CNN to pick the right cover image
  • LiitoKala 34B 18650 — first impressions in a Waveshare UPS 3S

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Marc de Mas
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