[Henielma]

You are completely right! That is the trick. My LabVIEW application does the bitbanging.

Only disadvantage nowadays is that it becomes more difficult to find a PC with a parallel port. Nowadays is a USB port more logical to use.

[S. cerevisiae]

Yes, the IEEE 1284 parallel port is a dead-end street when it comes to embedded system interfacing today. 

[redbeerman]

And Windows is not so good when you have real time interrupts that need to be dealt with.  It usually prioritizes it's own first, like updates and other outside world stuff.  For good process control a RTOS is almost essential.  But you guys know this already.  A lot depends on how much you have going on, just controlling temperature or handling functions that occur over minutes as opposed to milliseconds it may work OK.  I've seen it go both ways depending on the application. Cool system.  I'm a little hesitant about putting heaters in plastic buckets.  A single fault and you may have a fire if there is not water there.

[Henielma]

The cycle time for my Labview applications is 1 second so it is not very hard real-time. But you have a point for more time critical processes.

The heater in the plastic bucket is no problem when there is at least 4 liters of water in it. With less then 5 liters of water in the bucket I disconnect the power to the element. And also the chips fryer element has still two protections against overheating. The first is the original thermostat which I set to 90 degrees C and the second protection is the original overheating protection of the chips fryer. Both are in series with the PC temperature control and switch off if over temperature is reached.