Hello Everyone,

I am a newbie to the world of PIC devices having a distant history with the
6809 family.

Am looking for some system design guidance from those of you for whom my
task is old-hat.

I have not yet chosen a device or indeed a programming/development
environment so any input, without causing a "mine is better than yours" type
war, would also be appreciated.

The specs follow (sorry in advance about the length of the story):-

Up to 4 independent sensors, each with an RS232 output at 1200 baud, no
parity, 8 bits and 2 stop bits, produce a near continuous data flow which
may include a warning or alarm message in the format *W1 or *A1, where the
numeral may be between 1 and 7. There is no synchronisation of serial comms
between any of the 4 instruments.

Each of the 4 data streams is to be examined for any alarm/warning and then
produce an output current (4..20 mA) proportional to the largest magnitude
of the trailing numeral. So A1 would be greater than any W#.

My first concept goes as follows. Four opto isolators accord protection and
produce 4 unipolar data streams, one for each sensor, which are directed to
a PIC device for each channel. Each PIC tests for the telltale leading *
character. It then tests for a W or A as the next character and finally
extracts the number. An alarm number is then offset by say a value of 7.
This offsetting then yields warnings from 1..7 and alarms from 8..14. A
value of 0 would indicate the absence of any warning or alarm.

Each channel's value would then be written to the parallel output of its own
PIC and latched. These outputs would then be fed to a small combination of
say 4585 4 bit magnitude comparators so that the largest value of the 4
channels of warnings/alarms is finally available to drive a DAC and thence
produce a 4..20 mA output proportional to the warning/alarms (4 mA being the
all-OK level).

Questions:-

1. I am assuming that the RS232 data streams must have dedicated PICs.

2. Would a newbie be able to produce this level of processing without going
bald or should a Basic Stamp version be used?

3. Should the comparator/DAC combination be replaced by a PIC with a PWM
output feeding a filtered OpAmp stage?

4. Which development machine could be used economically for a production of
say 10 units?

Appreciate all and any insights.

Regards,

Ross McKenzie
Melbourne Australia