>...Your first task is to tell me what your personal "dream specs" for
> an SSU would be.  How would you like it to work to make your life easiest?
> What sort of granularity of measurement is needed?  Is 8 bits enough? Is 16
> bits too many?  Would you like the results scaled to inches? cm? metres? left
> as a raw count?  Should the data be presented in binary? ASCII? packed BCD?
> EBCDIC?
>
> - Rick "So many questions" Dickinson


Here's my wish list: I would like the SSU to use an I2C interface, with the
possibility to configure it to do the following:

1) Use Hardware General Call to periodically broadcast range readings to
the bus; this has the advantage that the SSU code wouldn't need to know
anything about the other nodes on the bus. Instead, the SSU would transmit
as a master the I2C addr. "00000000" followed by "AAAAAAA1", where
"AAAAAAA" its own address, then the range data. This mode should be
programmable for update rates varying from, say, 16 Hz to 0.0625 Hz.

2) Respond as slave to direct addressing requests to: a) configure update
rate & mode; b) return range reading now; c) configure setpoints.

3) Broadcast Hardware General Call when high or low setpoints are crossed.

4) A variant of 3: Broadcast Hardware General Call on delta.


Data returned: Time Of Flight (TOF) to nearest half millisecond in binary.
Second choice would be BCD. Use TOF instead of absolute distance because
seconds are the same in MKS and Conventional units, and each node can scale
this into desired range units if needed. Also, you can adjust for
temperature & altitude effects more readily.

For many applications, 8-bit resolution would be entirely adequate, which
would correspond to a dynamic range of approx. 3.0" to 844" (7.6 cm to 2140
cm), with the usable band of commonly available transducers being from 6"
to 360" (15 cm to 914 cm). If you choose BCD, though, you might as well use
two bytes of packed BCD.

--BN

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