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.
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
A seed for a note about where our data actually sits: from punched tape and the first hard disk to SSDs and NVMe, file systems, RAID – and why a NAS is called a NAS.
Structural Dynamics and Earthquakes
A seed for a note about what happens when loads move: natural frequency, resonance, damping, why bridges and buildings sway, and the basic idea behind designing for earthquakes in Slovenia.
How the Finite Element Method Works
A seed for a note about the method behind almost every structural program: how a structure becomes a mesh of small elements, what the computer actually solves, and why the mesh and the supports matter more than the colours.
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, and how I make my notes readable for Google with plain HTML, a sitemap and a small Python script.
Constructing a Backup
Why RAID and the cloud are not a backup, what the 3-2-1 rule really means, and how I back up my own data – with restic on a NAS, a test restore and a few stories of people who were lucky (and some who were not).
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