Typical PLCs (programmable logic controllers) are very expensive to get started with, often over $1000 for the hardware and the software. However, some PLCs can be had for less than $100 with free software. Here are a few cheap ways to get started in the world of automation with great (but cheap) PLCs.
A relatively new company to the PLC community, Velocio offers two low-cost PLCs that are ideal for people wanting to learn about ladder logic and PLCs in general. Starting at $49, the Ace offers basic functionality with 6 digital inputs and 6 digital outputs. Other configurations with different IO are available. Velocio's line of PLCs programs over a standard USB cable using free software.
AutomationDirect sells the Koyo CLICK series of PLCs in the American market. These are low-cost PLCs with industry applications in mind. This line of PLCs has gone through several different compliance tests such as CE and UL. With a handful of different configurations on the CPU module and 19 different output cards, this PLC comes with a lot for the money. The CPUs start at $69, have free software, and the programming cable is only $14, which makes the CLICK series another option at a reasonable price.
Divelbiss’ entire product line is made up of relatively lower-cost PLCs, with their cheapest being a product called the Micro Bear. This is an exposed board PLC, so depending on the application an enclosure may be needed. At a price of $99 for the CPU, $14 for a programming cable, and free software, this is another great low-cost option.
Smart Relays and Programmable Relays
A large product class that is worth mentioning is smart or programmable relays. Programmable relays are similar to PLCs but aren't as powerful. At times, though, these are grouped together with PLCs. These are ideal for small tasks since many of these "relays" can only support a few hundred lines of ladder logic and limited IO. These often require low-cost or free software. Many large companies make these, such as Omron, Crouzet, Phoenix Contact, Eaton, Rockwell Automation, and Schneider Electric. Smart relays should be considered in simple applications where a full PLC may be overkill. Programmable relay systems (CPU, programming cable, and software) can easily start below $400.
With PLCs becoming extremely cheap, they're a great option for simple automation tasks and there are tons of new applications for PLCs that were simply too cost-prohibitive before. They're great for automating interior and exterior lights, providing a new level of control for train layouts, simplify industrial automation that previously used relays, greenhouse controllers, or even to replace timer relays. Plus, these cheap PLCs can be a valuable learning tool for ladder logic, terminology associated with automation, and operation of PLCs. Have fun!