KNX is the open world standard for building automation (ISO/IEC 14543-3). Lights, blinds, HVAC, energy, security, all on a single bus where every device is intelligent and talks peer to peer. This isn't a brochure: press the buttons below and watch a real telegram travel the bus.
Auto-running. Lesson 05 hands you the controls.
In a conventional install, every switch is hard-wired with mains cable to the exact load it controls. Want that switch to also dim, or trigger a scene, or react to a sensor? You re-wire the wall. In KNX, switches and loads never touch each other. They both sit on one low-voltage bus and are linked in software. Re-purpose anything by changing a setting, not the cable.
KNX is ISO/IEC 14543-3 & EN 50090. Not one brand. 500+ manufacturers build interoperable devices that all share one bus.
No PLC, no server, no hub to fail. Every device has its own microprocessor and talks directly to the others, peer to peer.
An individual address identifies each device for programming. A group address is the shared "function" that links a sensor to its actuators.
Every certified device, any brand, is configured in ETS (Engineering Tool Software). Learn one tool, commission anything.
A single KNX line is the basic building block: a power supply, the green bus cable, and the devices that hang off it (sensors send, actuators switch loads). Couplers join lines into areas, and areas into a whole building. Tap a part of the diagram to inspect it.
Each part of a line does one job. Click any device in the diagram (or use the chips below) to see what it is, its real-world specs, and how it behaves on the bus.
KNX TP runs on a certified cable, usually green, J-Y(St)Y 2×2×0.8 mm. Only one pair is used for the bus: red = +, black = −. The second pair (white/yellow) is a spare. It carries data and the 29 V DC that powers the devices, so most devices need no separate supply.
Wire it however the building wants: branch, spur, daisy-chain. Mix them freely on one line.
Never join the bus back into a loop. A ring is the one topology TP1 forbids.
Max 1000 m total per line. ≤350 m supply→device, ≤700 m device→device.
The bus is SELV (safety low voltage). Separate it from mains; never let 230 V touch a bus terminal.
Add a power supply per line (choke built in). Need more? A line coupler starts a fresh segment.
A line holds ~64 devices. Stack 15 lines onto a main line through line couplers and you have an area. Stack 15 areas onto a backbone through area couplers and you have a whole building. Couplers also filter traffic, so a telegram inside one line never clogs the rest. Move the steppers and watch the structure grow.
This is a working KNX line. Sensors (amber) send a telegram addressed to a group address. The telegram is broadcast on the bus, and only the actuators subscribed to that group act on it. Press a sensor, watch the packet ripple down the green wire, and read the frame on the right. Then re-link the group addresses below and watch the same button do something completely different.
A KNX telegram is a short string of bytes sent at 9600 bit/s. Press transmit and watch each field clock out as a real waveform: control, the sender's individual address, the destination group address, the command, the payload, and a checksum. Then see how two devices that talk at once sort it out, no collision, no central referee.
Both devices listen first, then start together. Each bit is either dominant (0) or recessive (1). A device sending recessive that hears dominant backs off instantly. The lower address wins and keeps going. The loser simply retries. No data is ever lost.
A telegram's payload is meaningless until you know its Datapoint Type (DPT). A DPT says how many bits the value is and how to read them. A switch is 1 bit. A dim level is a 1-byte 0–100%. A temperature is a 2-byte KNX float. Pick a DPT and drag the value, the encoded bytes update live.
One single bit. 0 = Off, 1 = On. The smallest, most common telegram on any KNX line, every light switch sends this.
KNX is the logic; the medium is how the telegram physically moves. Twisted pair is the backbone of most installs, but you can mix in wireless for a retrofit room, ride the existing power lines, or jump between buildings over IP. The telegram is identical on all of them.
Everything so far, on one floor plan. Toggle a room and its actuator fires the light. Then press a scene: one telegram carries a scene number, and every actuator recalls its stored state at once, lights, dim levels, blinds. That is how "Movie", "Leaving" or "Good night" works in a real KNX home.
Every KNX project lives in ETS. You give each device a unique individual address (who it is, for programming), then create group addresses (what it does) and drag sensor and actuator objects onto the same group to link them. Build both below.
Identifies one physical device for programming. Format Area.Line.Device. Unique across the whole installation. The bus uses it to know exactly which device to download to.
The shared "function" that links devices. Format Main/Middle/Sub. A switch sends to it, actuators listen on it. Same group on two devices = they are wired together, in software.
Add the line, drop in every device, hand each an individual address.
Lay out the functions: Hall light, Living dimmer, Bedroom blind…
Drag a button's "switch" object and an actuator's "switch" object onto the same group.
Press the programming button, ETS pushes the config. The line is live.
Onwords designs, programs and commissions KNX from the single-line drawing to the final ETS download. Lighting, blinds, HVAC, energy and one app over all of it.