My unit (old 2.1 version) recently also stopped working. It does not start. Ray (thanks) tried to help me but without effect. So i had to do something quickly to water my garden (11 zones). Buying new unit takes a time. So I took raspberry, old SATA cable and connected this two things. According to source code you can use this pins to connect relay.
#define PIN_FREE_LIST {5,6,7,8,9,10,11,12,13,16,18,19,20,21,23,24,25,26} //
No soldering, only parts i used are relays, power supply, non modified opensprinkler software installed according to user manual.
Works quite well except rain sensor (it should be connected using PCF8591 – it is more time consuming to connect it.
I also tried to connect zone expander with shift register (2.1 version) then i will not need relays. Unfortunately i only found connection schema in OSpi manual from side of raspberry. I tried to analyse eagle PCB schema of zone expander but no success and i do not want to fry my expander. So for emergency you can try version with relays. Take a look at picture.
Regards
Piotr
