gEDA-user: another I/O port idea

[DJ Delorie]

> Is having -10V and +10V supply hard in your design?

Yeah, and not useful either - everything is 5vdc or 24vac outside the
box.

> Then your next stage can use a 10V supply to hard turn on some heater and 
> solenoid handling FETs.

The second stage just drives the thermostats - RS-232, 1wire, etc.
The problem is that the wiring used is existing 18g, non-twisted, long
runs.  EMI is a problem, I've already replaced one of the drive
transistors on the existing board, and I'd rather burn out a drive fet
than an MCU.  Plus the MCU doesn't have enough drive anyway (only a
few mA).

I did have the idea that a cheap dual op-amp could be used to provide
definite transition voltages and independent drive, though, plus level
translation.  You can get a dual op-amp for $0.50.

> For motor and power control signal runs, I am liking the idea of
> plastic optical fiber, master-slave, daisy-chained-repeater
> function, fail-safe-cut-cable, one-control-channel-per-wavelength,
> not tristate.

Overkill for a thermostat ;-)