Hardware
The hardware part modifies a Velux KLR100 remote control. This seems to be the cheapest way to access the windows, because the KLR100 is in scope of delivery.
The modification simply connects the buttons of the remote control to an optocouplers. The opposite side of the optocouplers are then connected to the Raspberryi GPIO pins. The optocouplers are needed because the KLR100 is using a 2x5 button matrix. A button matrix means that the buttons are connected in the following way to the microcontroller:
In my case I've used two Toshiba - TLP291-4 to connect the up button and the open/close button. The following circuitry was used:
I've used some magnet wire to connect the button traces on the backside of the PCB (see image).
The remote control supply voltage has also to be controlled by the raspberry. This allows to change the remote to a defined state. On the raspberry pi side i've used a NPN transistor to cut off the GND. The positive supply voltage is connected to the raspberries 5V pin.
After soldering the magnet wire to the appropriate button matrix signals, the remote control can be reassembled. The magnet wire and supply wires have to come out of the battery box. Next step is to connect the magnet wires to the optocoupler (see image).
Connect the secondary side of the optocoupler to the raspberry GPIOs.
Finally you can put everything into the battery box.
The optocoplers are connected to the following GPIOs:
- GPIO 22 <-> open Button
- GPIO 24 <-> close Button
- GPIO 23 <-> up Button (change Product)
- GPIO 17 <-> Remote control supply voltage