Bluetooth Low Energy Technology

Bluetooth Low Energy. Not to be confused with Classic Bluetooth – that old power-hungry audio dinosaur. BLE is the diet version. Less bandwidth, less power, less everything – but good enough for sensors and stuff that just want to say “I’m alive” once a minute. Not long range. Not LPWAN. Just... barely enough.

Vendor and URL

This lovely chaos is brought to you by:
Main vendor: Bluetooth SIG (Special Interest Group, but sounds more like a secret society)
Official docs: https://www.bluetooth.com
If the link's dead – welcome to the abyss of PDFs and member logins.

Technical Public Documentation

They wrote specs. Hundreds of pages. Usually buried in zip files inside zip files.
Full spec: BLE Core Spec @ Bluetooth SIG
GitHub repo: https://github.com/bluekitchen/btstack (for those who want to cry in C)
Read it if you’ve got a few months of free time and strong coffee.

Overview

BLE talks device-to-device. Great for wearables, sensors, trackers – basically things that need to whisper data every now and then. One central, many peripherals. Short bursts. Few bytes. And it all resets when you walk behind a wall. When it works, it’s magic. When it doesn’t, it’s rage.

Architecture

Central and Peripheral. That’s it. One talks, the other listens. Or not. Depends on mood. There’s also Observer and Broadcaster modes, but those are mostly for shouting into the void. BLE Mesh exists too – it’s like trying to make a social network out of shy introverts.

Device Roles

Central: the boss. Usually a smartphone or gateway. Peripheral: the worker bee. Sends data, does as it's told. No routers in classic BLE. In Mesh, everyone’s a router – in theory. In reality? Half the nodes flake out and go silent when the fridge compressor kicks in.

Channelization

BLE lives in the crowded 2.4 GHz band. Same house as Wi-Fi, microwaves, and angry cordless phones from 1998. 40 channels total. 3 are for advertising. 37 for data. Adaptive frequency hopping is supposed to help. Usually just makes debugging harder.

Frames

BLE packets are tiny. Real tiny. Like "I fit in 47 bytes" tiny. Headers, payload, CRC – you don’t get much room. Payload size depends on the version – BLE 5.x gives you more if you ask nicely. Some frames are obvious. Some feel like eldritch runes etched by protocol demons.

Networking

Classic BLE is not mesh. It’s star. One central, many peripherals. BLE Mesh changes that – sorta. Nodes relay messages like gossip at a family BBQ, hoping someone hears it. No IP by default, unless you add something like IPv6 over 6LoWPAN over BLE – yeah, don’t.

Security

Yes, there’s encryption. AES-CCM with 128-bit keys. Pairing methods: Just Works (insecure), Passkey (semi-secure), and OOB (good luck). Bonding stores keys for future connections. Security level depends on what you enable – or forget to enable.

Networking Process

Peripheral advertises. Central scans. They find each other. Connection is made. Pairing optional. Data gets exchanged in GATT format – basically a glorified key-value store. Then comes disconnection, reconnection, and repeat until someone gives up or changes battery.

Use Cases

BLE runs half the smart world: fitness trackers, smartwatches, tags, earbuds, lightbulbs, toothbrushes, thermostats. It’s cheap, small, and barely sips power – until you flood it with notifications. Not made for big data. But for “Hey, I moved 3 steps”? Perfect.