JPNAS.NET / Digital Garden
My Digital Garden – all notes
Notes and articles about computers, networks, self-hosting, security, AI and engineering by Jernej Pleteršek. Each note is also available in the interactive Digital Garden with search and filters.
When Is a Device Too Old? Phones, Computers and the Planet
Is an iPhone 12 ready for the bin, is a seven-year-old computer useless? How to check the hardware with free tools, how long devices really get updates, what wears out and what doesn't, whether new is really new, what a device costs the planet before you switch it on, and when used or refurbished is the smarter buy.
When Someone Uses Your Name: Identity Theft and Impersonation
Strange e-mails, a fake profile, a loan you never took: how somebody can misuse your identity, real cases from Slovenia and abroad, what the warning signs mean, what to do in which order (with the Slovenian addresses), and the foundation everybody needs today – including what AI changed.
Integrals Without Fear
What an integral really is and what it is for in practice: cut the area into strips, multiply and add up. How much in total, what is the average, where is the middle – with the electricity bill, a rainwater tank, earthworks, a plot of land, water pressure on a pool wall and heating, plus Archimedes, Leibniz and a beam in Python.
Tokens and Context: What Happens to Your Message
Why an AI forgets, why long chats get slow, and what skills are for: tokens and the context window from 512 tokens in 2018 to a million today, what really happens when you press Enter, the KV cache, RAG, tools, memory and skills – with a tokenizer in 30 lines, a chat simulator and a local model in Ollama.
Structural Dynamics and Earthquakes
What happens when loads move: natural frequency, resonance and damping, the Ljubljana earthquake and the bridges that taught us, the response spectrum and the new Slovenian hazard map, and why ductility matters more than strength – with a frame by hand, three storeys in Python and a footbridge that bounces.
How the Finite Element Method Works
What happens inside every structural program: from a single spring to the stiffness matrix, element types, meshes and convergence, singularities and the classic mistakes – with a stiffness matrix by hand, a cantilever from small elements in Python and the same check in FreeCAD.
Constructing a Weather Station
A seed for a small project that puts several notes together: an ESP32 with a temperature, humidity and pressure sensor, data over MQTT into a database, and graphs in Grafana on my home server.
How Storage Works
Where our data actually sits: from IBM's one-ton disk in 1956 to SSDs and NVMe, how a hard disk and a flash cell really store a bit, why SSDs wear out and what TBW means, what a file system and RAID add – and how to read the health of your own disks.
Constructing a Smart Home
Early notes for a smart home that works without the cloud: Home Assistant, MQTT, Zigbee and ESPHome, and how my network door opener fits in.
How Encryption Works
From Caesar and Enigma to AES and public keys: how encryption really works, the difference between encrypting and hashing, why passwords are stored with salt, and a few small examples you can try on your own computer.
Troubleshooting Networks
"The Internet doesn't work" – a step-by-step way to find out where it really stops: cable, IP address, router, DNS or the service itself. The commands I use on Windows and Linux, and what their answers mean.
Constructing a Website
From the first web page at CERN to this site: what really happens when you type an address, why a static site is often all you need, how I make my notes readable for Google and AI with plain HTML and a small Python script, and how to put a site on your own domain with free HTTPS.
Constructing a Backup
Why RAID and the cloud are not a backup, what the 3-2-1 rule really means, what AI changed about it, and how I back up my own data – restic on a NAS, a test restore, an image of the whole disk and a copy outside the house.
Computing with Switches
A working adder made of ordinary switches and relays, checked by a Python script before building, the same adder on an Arduino and in Logisim – and a look at everything a modern processor already has built in: floating point, text standards, encryption and more, with seven examples.
From Source Code to Silicon
What really happens when you run a program: from NAND gates and a processor's fetch-decode-execute cycle to bytecode, assembly and machine code, who compiled the compiler, Ken Thompson's Trusting Trust, bootstrapping from a 357-byte seed, firmware, Windows and whether a country could build everything itself – with six examples, including a program written byte by byte.
Constructing a Database
From punched cards and Codd's relational model to SQLite, PostgreSQL and NoSQL: how a database works, which one to choose for what, and four tested examples – a hiking database, a million sensor readings with an index, SQL injection and transactions, and a PostgreSQL server with users and backups.
Constructing a Program
From Ada Lovelace and punched cards to Python, Rust and AI assistants: how a program is made, which language to use for what, how source code becomes a running program, and four small examples – the same program in three languages, Git, tests and an automatic backup on a home server.
Structural Statics
Why buildings stand: a short history of statics from Archimedes to the finite element method and the Eurocodes, the basic principles, and step-by-step calculations of a beam, a truss, a column and a continuous beam – by hand and in Python.
Privacy of Smart Devices: TVs, Speakers, Cameras and Cars
Televisions, speakers, cameras, watches, vacuums and cars: a bit of history from the first connected vending machine to today's lawsuits, what these devices know about you, which protocols and services they use, and how to audit them, separate them from your network and keep control.
How Safe Is Your Phone?
Apps that collect data, why Facebook shows ads for things you only looked at, whether a phone can listen through the microphone or watch through the camera without you knowing – with a bit of history, iPhone, Android and GrapheneOS compared, and practical steps to see and control what your phone does.
Troubleshooting Windows
A method for finding out what is really wrong, how Windows starts and where it breaks, the tools that are already built in, the usual symptoms with the first things to check, and when it is time to stop repairing and reinstall.
How AI Works
What really happens inside an AI model: from a single artificial neuron to the transformer, how learning works with gradient descent and backpropagation, and how the code of a language model is built, and whether AI models are really open source – with five small Python examples you can run yourself.
Constructing an AI
Where artificial intelligence came from, how a modern language model is built and how it works, and how to run your own private AI assistant on a home computer or server with free, open-source tools.
Troubleshooting Linux
A method that works on every distribution, how Linux starts and where it breaks, the commands I would use first, the usual symptoms, worked examples from a full disk to a broken boot loader, and when it is cheaper to reinstall.
Constructing E-mail – Your Own Mail Server
How e-mail works, where it came from, what was used and what is used today, and how to build your own mail server – with practical examples.
Constructing a Cloud
Where the cloud came from, what it is made of, which services and protocols it runs on, and how to build a small one yourself on a Raspberry Pi or an old PC with Debian or the Red Hat family.
Computer Networks
What a network actually is, a short history of connecting devices, the protocols of yesterday and today, what to watch out for when configuring a router, VLANs and VPN, and how to build your own router with open-source software.
Reviving an Old Computer with Open-Source Operating Systems
Windows 11 can no longer be installed on your old computer? Open-source alternatives can bring it back to life. Plus a bit of operating system history and who uses what today.
Microcontroller Communication
Exploring MCU, MPU, SoC semantics, Nextion displays, Arduino Cloud, eWeLink and your own MQTT / Home Assistant server.
Communication with the Machines
Exploring the layers of interaction between humans and devices, from GUIs and terminals through protocols and serial lines to low-level assembly and quantum computing, with hands-on examples.
Security Considerations
Threat models, the GDPR, cryptography in practice, accounts, devices, backups and networks: how to think about security in the digital space, plus a checklist for one evening.
Network Door Opener
Electrical, Solar, Wind or some other Energy driven Network Door Opener, with eWeLink, Home Assistant or your own MQTT server and app