Charly's Column – libcoap

Trådlös is the Swedish word for "wireless" and thus throws light on the name of the TrÂdfri smart lighting system. In the simplest case, you combine a lamp with an actuator: A remote control, a dimmer, and a motion detector are offered.

If you also want to use an Android or Apple smartphone to control the light source's brightness – and in many cases also modulate the light temperature from cold to warm white – you need a gateway, which is a small control box that connects to your Ethernet network and sends commands to the lighting systems. ZigBee Light Link [1] acts as the protocol in this case, but customers also can use compatible lamps with E14, E27, and GU10 sockets and LED panels that can be hung on the wall or built in to furniture.

That's all quite nice, but, of course, I do not want to control everything with an app. Instead, I want the lighting system to adapt dynamically to the ambient light, such as gradually becoming brighter at the onset of dusk. The Linux PC that evaluates the data from my photovoltaic system knows when it turns dark (otherwise, a simple brightness sensor will do the trick), and it is precisely this Linux PC to which I want to pass the Ikea gateway commands so that it can pass them on to the lights.

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