Summary
Top-level Article: DigiKey Product Selection Guides
This page focuses on programmable controllers (PLC, PAC). It introduces the key technical parameters used to describe these devices and explains how to use DigiKey’s parametric filters to evaluate and compare PLCs by function, expandability, and integration fit.
For a hands-on example, see this DigiKey part search case study.
Key Selection Criteria for Choosing a PLC
Before selecting a PLC, it’s important to understand the parameters that define how it functions and integrates into your system. The following attributes appear in DigiKey’s parametric filters and are essential for comparing programmable logic controllers based on your application needs.
A 
icon has been added to highlight the top selection criteria for learning and lab-based applications. These are especially relevant when selecting a PLC for classroom use, skill-building, or rapid prototyping.
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Number of Inputs and Type:
Indicates the number of signal input circuits with which a device is equipped, and whether those inputs process applied signals as continuous (analog) or discrete (digital) values. -
Number of Outputs and Type:
For devices having built-in outputs, indicates the number of such outputs and the manner of their implementation. -
Expandable:
Describes ability to expand device functionality through addition of modular hardware extensions. -
Voltage - Supply:
Typically represented by a range, this indicates the low and high voltage limits which one can expect standard operation. Voltages outside this range may damage the device and other system components. -
Display Type:
Describes the user interface for indication. -
Number of Characters Per Row:
For products incorporating a segmented display, the display width in terms of number of alphanumeric characters that can be shown on each row of the display. -
Communications:
Enumerates communication interface(s)/protocol(s) implemented by a controller. -
Memory Size:
The amount of memory available in the device for program storage. -
Mounting Type:
Indicates how the device is attached. -
Features:
These are different capabilities or properties of the device such as battery backup or a cable. -
Software:
Identifies the recommended software suite for programming or monitoring of a device.
Real-World PLC Examples (With Links and Datasheets)
The following examples illustrate entry-level, mid-range, and high-end programmable logic controllers (PLCs) available through DigiKey. Each includes a product link, datasheet, and key specifications to help guide your selection. These models were selected based on their availability, representation of distinct application tiers, and suitability for both lab use and real-world deployment.
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The Arduino brand Opta WiFi is a modular PLC that may be programmed from the Arduino IDE. Expansion modules are available. Datasheet
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The Schneider Electric brand Modicon TM241CE40T is medium sized PLC that may be expanded using plug-in as well as expansion modules. Refer to the Product Selector tool on the manufacturer’s webpage for configuration options. Datasheet
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The Siemens Simatic S7-1500 is high-end PLC. This PLC has zero built in I/O. Instead, it is designed to work with remote I/O. Please refer to the Siemens TIA selection tool to identify supporting I/O. Datasheet
PLC Feature Comparison: Entry-Level, Mid-Range, and High-End Models
The table below compares the three representative PLCs. It highlights application tier, built-in I/O availability, and expandability to help you identify a PLC that fits your project scope and skill level.
| Brand | Model | Application Tier | Built-in I/O | Expansion |
|---|---|---|---|---|
| Arduino | Opta WiFi | Entry-level | Yes | Yes |
| Schneider | Modicon TM241CE40T | Mid-range | Yes | Yes |
| Siemens | S7-1500 | High-end | No | Yes (Remote I/O) |
Frequently Asked Questions
What is a programmable logic controller?
Programmable Logic Controllers (PLCs) are flexible automation control devices that implement a real-time control algorithm, where actuators are controlled in response to sensor inputs. Complexity varies from simple devices capable of performing elementary logic and timing functions to advanced Programmable Automation Controllers (PACs) capable of orchestrating the motions of complex moving equipment such as material handling robots. These systems are often modular and extensible, to adapt to the needs of your specific application.
Which PLC features are the most important?
Each feature has meaning but not all features are important to every project. If you are new to PLCs, we recommend starting with the features marked with the icon.
Related media links
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Follow up
If you have any general questions on the specifications for a PLC, please reply using the button below. If you have questions on a specific PLC, please post your questions in the Industrial Automation and Control category.
AI tools were used to support the initial drafting of this article. The final version was reviewed and approved by DigiKey’s technical content team, drawing on hands-on product experience and customer engagement.