Hi Russell,

Every thing you have said is correct.

Thank you for the references. I will have to look into commercial solutions to bring myself up to date.

I was thinking of a board with a lot of dip switches on it and you had to write a basic like program on a computer that is downloaded into the board via the comm port. I have seen a lot of those in HVAC installations.

In other days a Potter and Brumfield relay with some discrete 74LS00 logic would have been used to fix the job. To stay in business you learned what worked real fast and got repeat business. Eventually it migrated to embedded processors and things were more complicated but still required a lot of knowledge to get the job done.

I don't see much has changed except the price has come down a lot and things have become more easier to get.

Regards,

Charles Bannister