i've built a vista20P alarm monitor for Hubitat. I received a lot of help of @ogiewon.
It is based on a ESP8266 board with some simple signal conditioning. It does not require any other hardware that the ESP8266 and a few electrical components. I would say it is 2/3 Arduino and 1/3 Hubitat.
I would be happy to post it if there is interest.
By monitor I mean the Hubitat "device" only receives the panel text from the Vista20P. I purposely have not included any capability to talk back to the Vista20P.
The project would include:
- Arduino - ESP8266 code
- Hubitat groovy driver
- Kicad PCB design
John