Question about DC ports 1-3

[Rob F]

The DC backup ports are inline on the signal wire so they don't carry any load, if the float is open it cuts the GPIO signal going to port which will turn it off no matter what happens on the Raspberry Pi. This means there is nothing to setup in reef-pi as they are hardware based. Maybe the Pi fails after turning on a DC port, the backup float will still work.

So they add an extra layer of protection but can also be used on their own if you run low on sensor ports. For example, maybe you have a light in a cabinet and you want it to come on when cabinet door opens and off when closed. All you need to do is leave the DC port turned on in reef-pi, add any on/off switch wired to backup float port will do the switching.

https://www.google.com/search?q=on/off+s...af9HtN5tWM

You could even wire multiple switches in series, if any one of the open the port goes off.