I am currently working on an unusual design.
I intend on using a PC running Labview for monitor and control.
However the electronics are a bit unusual compared to the other systems out there. I plan on using the 1-wire devices from Dallas/Maxim.
The 1-wires devices include temp sensors ( with alarms ), adressable switches ( similar to X-10 but for low voltage apps ), Analog to Digitial converters, and other devices.
I plan on using the addressable switches to control latching relays which, in turn, drive solid state relays. This allows the computer to set the state of the latching relay to turn on & off AC loads. The beauty here is that if power is cycled on the entire system, the AC power switches remain in the same state as before the power outage. This should be OK until the control system gets back in control.
The temp sensors will just be dipped in epoxy and used as temp probes.
The AtoD converters will be used for ph & orp probes if they prove to have high enough internal impedance. If not, I will need to incorporate instrumentation op amps.
The beauty of these devices is that they are very cheap ( $1-3 a piece ), and they can ALL be ganged together and controlled over only two wires. They can be "bussed" all through cat-5 enet cables or twisted shielded pairs. Most of the devices wont even need their own power, they are 'parisitically' powered from the serial lines.
The eval kit should be here any day, and I already have some labview experience. The NI website has labview VIs for driving the devices, I just need to upgrade to LV 7.1 or earlier. That should happen this week.
If I can get most of it working through labview, I would then prefer to port the controls to C code and run it on a linux box ( far more dependable ) with a dedicated UPS. I am even considering using an old XboX with the linux hack installed. All these devices can be driven from one USB port, and the XBox has multiple.
I'll start a thread if it looks promising.
Bean have you experimented with the different SSRs?
Or do you prefer the basic Digital Output Modules?
Stu