7 years, 11 months ago.

The ebay page shows a module with the PCF8574. That device has a default I2C address 0x4E (mbed format) since by default the module sets A0-A2 at logic high. However, I have seen the same module with the PCF8574A. The default address for that version is 0x7E (mbed format). Looks like you have that type. The analyser will only display the slaveaddress and no data because the mbed I2C routines dont get an Ack from the slave and abort.. The Ack (bit 9 of a communication frame) is missing (high level) because the Slaveaddress is wrong.

Try this approach:

First update the TextLCD lib (right click on the lib in your project) to make sure you have the latest version

Open the lib and adapt the TextLCD_config.h file, select LCM1602:

//Pin Defines for I2C PCF8574/PCF8574A or MCP23008 and SPI 74595 bus expander interfaces
//Different commercially available LCD portexpanders use different wiring conventions.
//LCD and serial portexpanders should be wired accordingly.
//
//Select Serial Port Expander Hardware module (one option only)
#define DEFAULT   0
#define ADAFRUIT  0
#define DFROBOT   0
#define LCM1602   1
#define YWROBOT   0
#define GYLCD     0
#define MJKDZ     0
#define SYDZ      0
#define WIDEHK    0
#define LCDPLUG   0 

Declare the display:

TextLCD_I2C lcd(&i2c_lcd, 0x7E, TextLCD::LCD20x4); // I2C bus, PCF8574A Slaveaddress, LCD Type

Compile and run the code

Make sure the LCD contrast is correct. Adjust the blue potentiometer on the i2C portexpander module. Voltage on pin 3 of the LCD will be close to 0.5 V but that depends on the LCD. What contrast voltage did you use for the parallel port version? You will probably already see dark rectangles on the display when the power is on, even without running any code.

That should work..

 lcd.setBacklight(TextLCD::LightOn); 
 lcd.setBacklight(TextLCD::LightOff); 

// Set and show user defined characters. A maximum of 8 UDCs are supported by the HD44780.
// They are defined by a 5x7 bitpattern. 
  lcd.setUDC(0, (char *) udc_0);  // Show |>
  lcd.putc(0);    

  lcd.setUDC(1, (char *) udc_1);  // Show <|
  lcd.putc(1);