40-way Ethernet Digital I/O extension for Loxone

I’ve nearly completed building my own home, and have used the loxone mini-server to supply the home automation.  When specifying the server, we quickly realised we would have to find another solution for all the digital io.
We have 43 light switches – but each light switch has 4 contacts – making 172 inputs just for the light switches.  Add to that 20 door & window sensors, plus blind controls, PIR sensors, under floor heating actuators and pumps.  You get the idea.
I chose the teensy 2.0++ as it had a large number of digital IO on the board.  We did consider using I2C io extension boards, but physical size is a factor and it was easier for us to make it compact using the teensy.
I’m not a hardware expert at all!  But the system we have made is bullet proof reliable.  The software and interface to the loxone does not use any polling at all- so all the double/triple clicks work flawlessly with the loxone system.
The boards have a web interface which is really important for setting up and diagnostics as you have feedback showing which inputs or outputs are active.

In our build we have 2 sub-boards each with 4 nodes – making a total of 8 nodes with a capacity for 320 i/o.  Each sub board has it’s own 5v 5 port switch, and a POE splitter – the whole board being run by 1 port on my POE switch.

It was a challenge to get 40 I/O available on the teensy 2.0.  We needed 4 pins for the ethernet connection & 1 pin for the on-board LED.  Using the teensy’s interior pins, and re-purposing one of the UART pins we were able to have 40 pins usable for io.  The UART pin needed an external pull-up resistor to make it usable for normal io.