Arduino I2C display

Question

Hello: I'm a hobbist electronics student and I have been experimenting with arduino for a while. I have worked with character and graphic LCD without any serious problems. I wanted to save wires, so I bought an I2C LCD 20x4 module from ebay. However I have not been able to get it working. I have downloaded the most recent I2C library and I have followed all the instructions but my LCD simply won't work. Instead it lights up like this. The supplier told me that the address of my display is 0x27, but when I use this address nothing happens. After trying different addresses, I dicovered that if I use 0x20 as an address some characters blink randomly with the example code running. the chip on the board is the pcf8574 from Phillips. 
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billabott · Accepted Answer

Extract from TerryK's notebook: //---(Following are the PCF8574 pin assignments to LCD connections )---- // This are different than earlier/different I2C LCD displays #define BACKLIGHT_PIN 3 #define En_pin 2 #define Rw_pin 1 #define Rs_pin 0 #define D4_pin 4 #define D5_pin 5 #define D6_pin 6 #define D7_pin 7 #define LED_OFF 1 #define LED_ON 0 /*-----( Declare objects )-----*/ LiquidCrystal_I2C lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin); The above expanded library interface makes clear to me that the vendors could have wired the 4 serial control and 4 data pins of the LCD any old way (actually 8! = 40,320 ways) they choose to onto the PCF8574's output pins. So, why is it that the vendors don't provide that info to make their devices understandable and useable to the open source community? Everyone, who has bought one of these I2C LCD units should contact the vendors and demand on behalf of the OS community that the interface between the PCF8574 output and LCD control/data lines be PUBLISHED on the web, IMHO.

billabott · Answer

#include #include LiquidCrystal_I2C lcd2 = LiquidCrystal_I2C(0x27,20,4); // Set the LCD address, # columns and # rows // Create a set of new characters const uint8_t charBitmap[][8] = { { 0xc, 0x12, 0x12, 0xc, 0, 0, 0, 0 }, { 0x6, 0x9, 0x9, 0x6, 0, 0, 0, 0 }, { 0x0, 0x6, 0x9, 0x9, 0x6, 0, 0, 0x0 }, { 0x0, 0xc, 0x12, 0x12, 0xc, 0, 0, 0x0 }, { 0x0, 0x0, 0xc, 0x12, 0x12, 0xc, 0, 0x0 }, { 0x0, 0x0, 0x6, 0x9, 0x9, 0x6, 0, 0x0 }, { 0x0, 0x0, 0x0, 0x6, 0x9, 0x9, 0x6, 0x0 }, { 0x0, 0x0, 0x0, 0xc, 0x12, 0x12, 0xc, 0x0 } }; void setup() { int charBitmapSize = (sizeof(charBitmap ) / sizeof (charBitmap[0])); lcd2.backlight(); // Switch on the backlight // lcd2.begin(20,4); // initialize the lcd for ( int i = 0; i < charBitmapSize; i++ ) { lcd2.createChar ( i, (uint8_t *)charBitmap[i] ); } lcd2.home (); // go home lcd2.print("Hello, ARDUINO "); lcd2.setCursor ( 0, 1 ); // go to the next line lcd2.print (" FORUM - fm "); delay ( 1000 ); } void loop() { lcd2.home (); // Do a little animation by writing to the same location for ( int i = 0; i < 2; i++ ) { for ( int j = 0; j < 16; j++ ) { lcd2.print (char(random(7))); } lcd2.setCursor ( 0, 1 ); } delay (200); } This compiles clean: Got a clean compile with this sketch. and this one: #include #include LiquidCrystal_I2C lcd=LiquidCrystal_I2C(0x27,20,4); //set the LCD address to 0x27 for a 16 chars and 2 line display void setup() { lcd.init(); lcd.backlight(); lcd.setCursor(0, 0); lcd.print("b2cqshop"); lcd.setCursor(0, 1); lcd.print("Voltage: "); lcd.setCursor(13, 1); lcd.print("V"); } void loop() { int val; float temp; val=analogRead(0); temp=val/4.092; val=(int)temp;// lcd.setCursor(9, 1); lcd.print(0x30); lcd.print(0x30+(val%100)/10); lcd.print('.'); lcd.print(0x30+val%10); delay(100); } So please report back if it actually works with the I2C LCD. thanks. And give me my points. I earned them tonight.

Arduino I2C display

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