My understanding of the project is to make two devices. The two devices
being a remote device and a local device. The remote device will sense if
each of two appliances are either on or off, and send the information to the
local device for display. If there is a failure in the system, some one will
get yelled at for leaving their cloths in the washer.

Would "not being yelled at" be considered "Mission Critical"?

I think that the sensors for the remote device should be cheep, simple to
interface and fun. With "fun" being important. Different uses for common
objects. The computer could integrate or differentiate the input signal
using a simple algorithm.

////////

Is input one on?

No

Has input one been on in last twenty seconds?

No

Then input one is probably not on.

/////////

It is only necessary for the remote unit to transmit data, and the local
unit to receive this data. As only four states are possible, the data
encoding can be simple. A simple way to do this is to use a form of Morse
code or CW transmition. Yes, dits and dahs.

////////////

The following relationships exist between the elements of the code (dits and
dahs), the characters (letters) and the words:
The DIT is the Basic UNIT of Length.
The DAH is equal in length to three DITS.
The space between the DITS and DAHS within a character (letter) is equal to
one DIT.
The space between characters (letters) in a word is equal to three DITS.
The space between words is equal to seven DITS.
(Source: U.S. Army Technical Manual TM-11459/TO 31-3-16 - Sept. 1957)

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So if a dot is a binary zero and a dash a binary one, the start bit could be
a dash, or three time slots. This time could be divided by two on the
receive side and used to determine weather the next two bits are dashes or
dots, 3 or 1. If less than half the start bit, it is a dot. Else it is a
dash. And no signal for a dash time (3) shows end of data.

With the sensors the effect of ambient noise and drift due to age and
temperature can be somewhat mulled out by taking a reading with no signal
present (appliance off) and using this value as a "floor" for the input.
This calibration can be done upon power up of the remote and/or with a push
button on the remote unit.

As a "fail Safe" feature, the local unit could have a preset timer function
that is set via a push button.

Bill



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