How much I/O do you need? Motor up/down takes 2, limit switches take 2,
and 2 for thermostat or serial temperature sensor. Then if you have an
operator interface you can get a serial LCD and 4 inputs for select
up/down, 1 for Enter, 1 for Back (or Esc). Parallax (among others) also
sells a ULN2803A chip that can drive 8 external relays up to 50VDC 1/2A,
complete with built in diodes for inductive loads.

I also installed a 1/rev contact to detect/count motor movement on each
motor. There are four of these motors total for a total of 20 IO here . I
also sense outside temp in addition to two inside temps and want to leave
room for a wind velocity sensor (future) - four more. Then there will be two
soil moisuture sensors and a water pump - three more. I'll need a couple or
four for an LCD read panel. I'd use any extras for a small operator
interface to do things like open or close everything. From experience, I
know to leave room for more IO, always seem to need it.

I'm not aware of this ULN2903A chip, I'll look into it




I bought a PIC32 starter kit from Digi-Key (Microchip has them for same
price), has a lot of I/O, 512K program memory, 32K ram, and a optimizing C
compiler with a 64K limit, all for $49.


Basic stamp is easy to program and well documented. I'm not at all
unconfortable with it. I feel just the opposite about working with C or
assembler. Plus, I'd be on my own for driving an Opto 22 board.

Karl