Maximum Number of Zones

[dan]

The 16 channel relay board you linked to is 12V. Not sure that could be used with the Pi.

You could use 2 8 channel 5V relay boards:
https://www.dx.com/p/zhaoyao-dc-5v-8-cha...25957.html

If you only need 16 stations you can use the relay_16 plugin for SIP and connect the relays directly to the Pi.
If you will need more that 16 stations then the DIY relay interface would be better.

another option is the TIAO Smart Sprinkler board which is all solid state.
https://www.diygadget.com/tiao-smart-spr...mobile-app

You can also get a 16 station expansion board to go with it:
https://www.diygadget.com/tiao-smart-spr...er%20board