Make: Technology on Your Time Volume 23

Photography by Tim Hunkin

BUILDING WITH PLCs

Programmable logic controllers never fail.

By Tim Hunkin

Programmable logic controllers (PLCs) are industrial computers about the size of a brick. Like microcontrollers, they loop through a list of instructions that repeatedly polls their inputs and generates outputs. But PLCs are larger and more expensive than microcontrollers, and they have much slower cycle times — usually no faster than 10 loops per second, unless you plug in special extra modules. And instead of programming them with C++ or BASIC, you use an arcane language called ladder logic (described later in this article).

Given these disadvantages, ...