Microcontroller
For comparison with other control technologies, Figure 14.10 shows the same machine tool operated by a microcontroller. As we know, the microcontroller uses signal levels around 5 V, so the input switches have to be connected with pull-up resistors. The microcontroller is programmed to operate the output loads via suitable interfaces, which allow its outputs to switch the high-power motors. These could be relays or three-phase contactors, but high- current field effect transistors (FETs) are useful here, as they can operate with 5 V inputs and have no moving parts. The microcontroller can be programmed in its native assembler
language (Program 14.2), or C, both of which take time to learn. This is why ladder logic was developed for programming PLCs, and the built-in interfacing in the PLC makes this the usual choice for such control applications.