dear all,

a friend who work at a small power plant asked me to developed
a simple telemetry system for his 3 substations (unmaned).

there was a telemetry/scada system implemented, but doesn't work
any longer.

he doesn't need a complete facilities like he used have in the past.
what he needs are:
- current measurement (maximum 4 analog input, 8 bit would suffice)
- breaker/circuit switcher status (maximum 8 digital input)
- trip/close coil operations (maximum 8 digital output)

all old transducer (4-20mA) and relays/coils are still in
good condition.

i've just completed an alarm project for the same plant.
the communication mesdium i used for the project is uhf radio (dtmf
signalling).
my friend is very sure that my alarm project can also be implemented
in his substation.

what i have in mind are:
- at88c55 + watchdog
- adc0809 and 4-20mA to 0-5V converter
- 8255 ppi
- mt8888 dtmf generator/receiver
- latch and address decoder
- good clean contact relays + terminal blocks
- visual basic program:
- poll routine to collect data/status
- interrupt facilities to control trip/close coils

i have no expertise in electrical power generation/transmission.
is there any special precaution for this environment?

thanks.