Hi, I need to use a heater to control the temperature of my work environment. The way i imagine this to be possible is to make a custom Gcode /Mcode which sets the desired temperature to my temp controller.

ex:
M850 1 58 Would set heater 1/sensor 1 to heat until 58 degrees at sensor location.
M851 5 40 1 Would wait for sensor 5 to read 40 degrees or more.
M851 2 35 0 Would wait for sensor 2 to read 35 degrees or less.
M852 1 1 Would wait for Heater 1/Sensor 1 to  reach set temperature.

Also i want to make the software read the current temperature to be displayed on one of the screens.



My proof of concept was making a arduino/modbus solution and it works! Now i have to remove the serial connection and do the same using nothing more than the options provided by the paralell ports provided by the Ethernet SmoothStepper.

Where do i start? What options are there?

I don't believe your going to be able to do that with an ESS. The ESS does not bring in any Analog signals, and that is the issue.
You will need sometype of way to bring in analog into M3.
For example:
1). a PLC with analog inputs that talk to mach3 over modbus (TCP or Serial)
2). as above but use your Arduino for the analog inputs over serial modbus
3). One of Peter Homans (Homan Designs) ModIO boards, or One of Aurturos (CNC4PC) products
4). some other device that will bring in the needed count of analog signals you need to process.
5). you may, or may-not need to do a PID loop (or several) internally, verses timouts on temp values.

Scott