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Small Open Source PLC Components and Source Files

Created on: 18 April 2013

Small PLC – Pages

In this part of the open source PLC project, we take a look at the components that are used to construct the small brick-type open source PLC.

The hardware source files including schematic diagrams and design files can be downloaded here.

PLC Construction Overview

The Small Brick Open Source PLC consists of three circuit boards:

  • CPU board that contains the microcontroller, analogue op-amp buffer IC, RS-232 IC, RS-485 IC, RTC IC (and backup battery) and EEPROM IC.
  • I/O board that consists of voltage regulator/power supply circuit, optically isolated inputs, optically isolated outputs and connectors for I/O, USB and JTAG.
  • Status board containing LEDs that display the presence of an input voltage, the status of the digital inputs and two programmable status LEDs. The status board also contains two push buttons for reset and programming.

The photo below shows all the components that are used to make the small open source PLC, including the circuit boards, ribbon cables used to connect between the boards and the case used to house the PLC.

PLC Components

PLC Components

PLC Boards Design Source Files

The boards were designed using Altium designer. The download below is for the Altium designer source files for all three boards.

If you would just like to look at the schematic diagrams for each board and do not have Altium designer, see the schematic in PDF format for each board below.

All new projects on the Starting Electronics website will be based on the open source KiCad EDA tools for schematics and PCBs.

Download the Altium designer PLC source files: (1.1MB) – needs the Altium designer software to view.

The Gerber files and drill files for this project are included in the above download.

PLC CPU Board and Schematic

Two images of the PLC CPU board are shown below. The CPU board is positioned under the status board in the PLC case with a reasonable clearance between the two boards. This puts the CPU board somewhere near the middle of the case.

PLC CPU board top view

PLC CPU Board Top View

PLC CPU board bottom view

PLC CPU Board Bottom View

The connector at the right of the board is for RS-232.

PLC CPU Board Circuit Diagram and Board Outline

PLC CPU Board Schematic: OSPLC1_CPU.pdf (27.4kB)

Board outline showing dimensions: OSPLC1_CPU_outline.pdf (32.1kB)

PLC I/O Board and Schematic

Top and bottom views of the PLC Input/Output (I/O) board are shown below. The connector on the right of the board is for RS-485.

PLC I/O Board Top View

PLC I/O Board Top View

PLC I/O Board Bottom View

PLC I/O Board Bottom View

PLC I/O Board Circuit Diagram and Board Outline

PLC I/O Board Schematic: OSPLC1_IO.pdf (41.1kB)

Board outline showing dimensions: OSPLC1_IO_outline.pdf (66.5kB)

PLC Status Board and Schematic

The single-sided status board is shown here. The RESET and TST buttons have not been soldered to the board.

PLC Status Board Top View

PLC Status Board Top View

PLC Status Board Bottom View

PLC Status Board Bottom View

PLC Status Board Circuit Diagram and Board Outline

PLC Status Board Schematic: OSPLC1_CPU_STATUS.pdf (8.9kB)

Board outline showing dimensions: OSPLC1_CPU_STATUS_outline.pdf (32.9kB)

← Previous: Small Open Source PLC Introduction