I will add the posibility for a KNX TP-UART2. If I don't have enough sercoms on my Atmel device, I will use zero ohm resistors to enable the KNX uart OR another function.

When I finish this project, I will have some very nice sensors that I will modify:

* PIR with separate Ambient light output and PIR sensor output. I have bought a cheap PIR from hornbach (12Eur, Q-link Wall mount sensor.). This pir is a ceiling pir for a round mounting hole in the ceiling. Just like a ceiling spot light. I will modify this PIR to have 2 separate digital outputs. 1 open collector digital output for the ambient light strength (PIR unit will handle the Lux threshold) and the other open collector digital output is for the PIR sensor. Separation enables me to switch the light with the Loxone when it's dark, but it will also enable me to use this PIR unit to enable the alarm (also when it's light, so during the day).

* CO2 sensor. I have found a cheap CO2 sensor on aliexpress. I will also use this sensor in my livingroom and bedroom to maintain a healthy climate in those rooms. It will switch the perilex socket of the Heat recovery ventilation (HRV). A humidity sensor will be used in my bathroom. https://www.aliexpress.com/item/MH-Z19-NDIR-CO2-Sensor-Module-0-5000ppm-new-and-original-in-stock-free-shipping/32697750985.html

* Windows/door sensor. For the windows and some doors I will not use a reed-relay, but probably a hall sensor with small PCB to make a open collector output. https://www.aliexpress.com/item/50-pcs-SS41F-41F-0H41-SH41-S41-Bipolar-Hall-Effect-Position-Sensors-SIP-3/1903012341.html

Most of these sensors will be handled after this extension PCB. Some of these sensors will be developed in parallel to this project.

PS. why am I not using reed relay and a normal relay? I want to use hall sensors and SSR because these semiconductor parts have no mechanical parts that can wear down. I want to make the system durable.