Hi Jan, Russel,

The intention of the board is that it'll be used to control my home automaton (or how do you call this?) system.

I'm now busy with a kind of simulation board, to see if everything I want to do is feasible. So, the drawings I posted are part of that simulation/test board.

But finally, the project I'm working on is to be classified somewhere in between hobby and commercial, since all controls of my whole house will have to 'run' on it. It's not a 'does it work? fine, does it not work? too bad' situation... ;-)

Controls such as detection of pressing the light switch button, control relays/contactors to put 220V on the outlets (or take it away from it), temp. measurement, light measurement, control of water pumps for the heating system, etc...

All this will be based on the I2c protocol. So, the processor will mostly take care of the 'clever' work, while the other components, will to the 'hard labour'.

The components which will mainly be used, are:
- PCF8574 for IO purposes (detection light switch control, so input, and switching relays, so output).
- PCF8591 for temp. measurement purposes (AD converter)
- TDA8444 for DA conversion (controlling of dimmers).

Those components will be isolated from the 'heavy' components by means of optocouplers, since I want a complete 'isolation' between the inside and the outside world. So, I won't control a relay directly from the PCF8574 pin, but an optocoupler will trigger a transistor on the 'other' side of the electronics, which will then control the relais.

But suppose I want to go outside with my uC ports, what buffers are most suited then, given the explanation above, thus knowing now that it's not intended to be used for extremely fast things?

Best rgds,

--Geert