The goal for this litle project was to learn the two-wire interface, which it makes possible to connect devices (up to 119) only with four lines: ground, power, clock and data. Please take a look on this piece of code, which demonstrates the use of the LCD display connected to the arduino uno board through the PCF8574 interface.
I used a standard library for the two-wire interface (Wire.h) and the LCD library (LiquidCrystal_I2C.h) by John Rickmann (originally by Marco Schwartz) from here.
The theory and praxis to the I2C is taken from the publication Interfejs I2C of Cezary Klimasz available here.

The internal address of the interface is 0x3F, which is calculated from the pin connectivity of A2-A0 lines on the PCF8574A. In this case all 3 lines are on high state (111) and together with the constant A6-A3 (0111) results in 0x3F for the 7-bit hex-address without R/W.

On power-on or when the reset button has been pressed the initialization of the LCD display occures.

LiquidCrystal_I2C lcd(0x3F, 16, 2);

On this osciloscope diagram one can see two digits (4 and 0 as ASCII code) transmitted to the display controller, each with a device address in front (0x3F).

This project is nothing special but it demonstrates the use of hardware in the high level environment.

The Unity software which is used for this simple project is used in the gaming industry. This project uses in addition an Arduino board to control the game. The player drives a small tuk-tuk car on the street. To control of the car four buttons are used connected to the input lines of AVR microcontroller, which in turn sends the ASCII codes through the serial line to the Unity software. The software reacts on pressed buttons turning the car to the left or to the right, accelerates or brakes the car.

Please see the code for connection to the Arduino board from the Unity software.

The Arduino is based on the Atmel 8-bit microcontroller ATmega328P. The switches are not pulled up to the voltage by 1kOhm resistors. The input state can still be stable because the pull up resistors are attached internally to the input lines inside of the microcontroller. By pressing on the switch, the corresponding input line is grounded and its state changes. The microcontroller can read this and reacts respectively. Further, a different value for each switch is transmitted through the serial port.

Please check out this very simple schematic. The implementation for it is even more simple. To forward the information a serial port on RS232 interface has been used, which can be max. 15m long.

The purpose for a servo driver is to set a desired angle of the servo-anker. The servo-motor is controlled with a pulse-width-modulation signal (PWM), thus a timer is used here. The schematic for the microcontroller-board used in this example and the detailed doxygen documentation are accessible by this link.

If you are courios to see the implementation of the servo-code, then please check out this link: servo.htm

The 74HCT595 is a 8-bit serial-in parallel-out 3-state shift register with output latches and is used to control of a 7-segment 4-digits LED-display. The datasheet for the IC can be downloaded here 74HC_HCT595.pdf and for the LED-display is here ldq-m284ri.pdf.

To see the implementation please check out this link: m1280_7segment.htm.

At my previous workplace I needed to grab the status of a machine and display it on a screen, so the staff will see it and reacts if needed. To realize the idea I invented a system contains of 3 parts – embedded device, database, windows application, which is including hardware and software solutions. The core point of the system is the embedded device, which is connecting to the machine with protocols (eg. USS, Modbus or H-protocol) and sending the data through the serial connection to the database.

How it works?

1. The embedded board sends a query message to the PLC or inverter.
2. The machine controller (PLC or inverter) responds to the embedded board the message with data.
3. The embedded board sends through RS232-connection the data to the database service application.
4. The database service application adds data to the database server including the data-stamp.
5. User interface gets the data and displays it.

For communicating with the hardware device on software level a protocol is needed. Only USS-protocol has been implemented. However there is possible to implement different protocols. A LCD-display was used for displaying informations and debugging purposes. The debug info cannot be send on the serial port, as both are obtained: one connects the PLC and another the PC-application. However, the app could have a debug mode to display the values from the embedded board. But it doesn't.

To connect the ethernut to the machine controller was necessary to build a RS232-RS485 converter. The schematic for the converter is accesible here. The MM75 (Siemens) operates with RS485 standard, while the embedded board operates with RS232.