Mini-ITX

A mini-ITX motherboard has no ability to control machines. In other words, there is no provision to control relays, read back the states of switches and measure voltages. In order to perform these tasks, you need to design and use another PCB connected to the mini-ITX system.

How much this costs depends greatly on your requirements. Utilizing an MCU (microcontroller unit), one can easily design and build small printed circuit boards with a variety of input/output abilities. For example, an ATMega128 (from Atmel) has about 48 input/output points that can be configured for CMOS/TTL I/O, PWM, UART, ADC and external interrupt applications. You still need to add interface circuits such as transistors, diodes and opamps to perform industrial control. It is easy to design such a printed circuit board, even route it by hand, because an MCU does not need memory busses.

The mini-ITX system can communicate with this extra PCB via many protocols. The easiest method is RS-232. Because RS-232 is widely supported by many operating systems, it is easy to debug the interface between the mini-ITX system and the extra PCB. For higher speed and more flexibility, some mini-ITX also has I2C busses. If you use an MCU with built-in USB support, all mini-ITX motherboards have USB support.