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PLµX IO interface

I2C, PCA9555, ADS7830

Inputs, Outputs, Analog Inputs

PLµX & IO-Interface.

Last modified: De Coninck Ivo

For coupling the embedded Linux board to various types of devices, relays and sensors an expansion board is needed. Here you can find more information on how to do this.


I2C Interface.

With two wires it possible to address up to 1136 members. IC2 is a synchronous bidirectional communication system that allows devices to transfer data using only two wires: a bidirectional data line (SDA) and a clock line (SCL).
Max clock rate: 400kHz.
The I/O board contains a PCA9555.

Three hardware pins (A0, A1, A2) vary the fixed I2C-bus address and allow up to eight devices to share the same I2C-bus/SMBus. The fixed I2C-bus address of the PCA9555, allowing up to eight of these devices in any combination to share the same I2C-bus/SMBus.

The PCA9555 is a Port-Expander with 16 GPIO-Pins, which can be controlled easily over I2C. Three device inputs (A0 - A2) determine the I2C address and allow up to eight I/O expander devices to share the same I2C bus. With a maximum of eight PCA9555 Port-Expanders the states of 64 inputs can be monitored and 64 outputs can be driven.

The first station with address number 0, corresponding to inputs and outputs 0.0 - 0.7 in a ladder diagram. The next station with address number 1, corresponding to inputs and outputs 1.0 - 1.7 in a ladder diagram, etc.

Port expander Board with 8 inputs and 8 outputs:
pca9555schema.png pca9555schema.png
Port Expander schematic.

Alternative: Gnublin Port Expander PCA9555.

  1. GNUBLIN_Module-Port Expander
  2. Quickstart for Gnublin Port_Expander
  3. Simple test board for Gnublin Port Expander.
    pca9555.test.IO.png pca9555.test.IO.png
    Schematic for Port Expander.
  4. Datasheet PCA9555


Digital 24 volt IO-interface.

Every PLC must have some means of receiving and interpreting signals from sensors such as switches, inductive and capacitive proximity sensors, liquid level switches, etc . And be also able to affect control over solenoids, valves.
The most common industrial signals are 24Volt DC. So we need to create a 24 volt interface card.
PLµX standard pin configuration for PCA9555:

Error found let me know. Thanks in advance.

  1. Download schematic and PCB. Created with Eagle PCB Design Software cadsoftusa.
  2. Schematic:
  3. PCB:


PCB test succeedded.

This figure shows the first successful PCB test.
The PCB with three lamps (24V, 2W) connected.


ADC interface.

The PLµX project provides maximum 4 GNUBLIN ADC-Modules(32 anlalog 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.
How To create Ladder Diagram with analog inputs.

Figure: Hardware setup.

ADC Hardware in action.


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