Raspberry Pi (Model B + V1.2) simple PLC usable for home automation

An attempt to implement a simple PLC into a Raspberry Pi single-board computer.

Ladder Diagram running light example: ldr.hlp.running.light.mp4
RPIPLC HW running light example: rpi.running.light.mp4
View Raspberry Pi PLC in action: potmeter.mp4

PLCs were developed in the 1960s to replace the complex electrical relay circuits widely used for machine control in industrial automation. Users program PLCs to define a series of actions that a machine will perform. The PLC works by reading input signals from devices such as sensors or switches and, depending on the value(s), turning outputs on or off.

In its simplest form, a PLC replaces relay logic. Instead of mechanical devices like interconnected relays or timers providing the logic for a machine or other device, the PLC is a single boxed device performing the same function. Because it is programmable and in essence a computer, it is more flexible, easier to change than physical relay wiring and a great deal smaller than the relay equivalent. It can also perform arithmetic and other functions, such as servo control and analog measurement.

Traditional PLC programming resembles a relay diagram, and for simple diagrams it has the same meaning. PLCs are usually programmed off-line, using tools running Linux or Windows. The text-based programs or ladder diagrams are compiled to an intermediate language that is downloaded to the PLC and interpreted. The PLµX project is an interesting study as an embedded controller. Like the PLCs it will replace, it is much more general than most embedded projects.

With a  Raspberry Pi board and the aid of eight GNUBLIN Module-Port-expanders the state of 64 inputs can be monitored and 64 outputs can be driven. The project provides also to add 4 GNUBLIN ADC-Modules ( 4 x 8 analog inputs).
This ADC module is used to measure voltages. The modules can be easily connected via a ribbon cable to the Gnublin Board or the Gnublin Module-Bridge.

A ladder diagram editor is also included. This Ladder Diagram Editor is designed to allow you to easily prepare a PLC program by simply placing blocks.
Ladder diagrams, which are in many ways similar to relay logic diagrams, are frequently used to graphically generate programs. When the instructions in the program are executed, the states of the inputs are monitored, depending on these states, various outputs are set either High or Low.

All functionality of the ladder diagram editor is available only under ubuntu. Other Linux distributions have not been tested.

With the Windows operating system, it is not possible to benefit from the on line features. Windows users can use a popular program named PuTTY to interact with the Raspberry Pi PLC.

Hardware configuration

The most important components.

1. Raspberry Pi model B +.
2. GNUBLIN Module-Bridge .
3. GNUBLIN Module-ADC .
4. Digital 24V IO-interface .
5. Empty.
6. Empty.
7. GNUBLIN Module-Portexpander .
8. Test board for Module-Portexpander.
9. 8 switches connected to 8 digital inputs.
10. 8 lamps (24 V, 2 W) connected to 8 digital ouputs.

How to start=>.