I currently have a circuit which consists of two different boards.
In the main board, there is a \$230\,\mathrm{V}\$ ac supply, a \$230\,\mathrm{V}\$ to \$12\,\mathrm{V}\$ dc power supply, a 7805 linear voltage regulator and other components as transistors biased on their collectors by the \$12\,\mathrm{V}\$ dc generated in the main board itself. On the another board there is a controller, powered from the \$5\,\mathrm{V}\$ supply generated by the main one: this controller drives the transistor located on the main board.
Now I want to use a separated \$230\,\mathrm{V}\$ to \$12\,\mathrm{V}\$ dc power supply for the controller board, so I'll be able to power my controller board from a \$3.3\,\mathrm{V}\$ power supply produced by using another regulator. So there will be two \$230\,\mathrm{V}\$ to \$12\,\mathrm{V}\$ dc regulators, one located on the main board and another on the controller board.
Now my question is:
Is it OK for the controller to drive transistors whose \$12\,\mathrm{V}\$ collector bias is generated from a different, separated regulator, however sharing the same \$230\,\mathrm{V}\$ dc grid voltage,?
I am also using an ADC which is measuring the output of a temperature sensor powered by the main board \$5\,\mathrm{V}\$ supply and sending its output to the controller board: could this create any problem? should I short the gnd terminals of both boards? Do I need to do anything else? Is this operation safe?