Hello, and thank-you for this code. I am working on a project with Crius 128x64 OLED and the code seems to work pretty well. However;

I can't get the oled.writeString(0, 0, "xx"); function to work. writeBitmap works but no printf function for the OLED. any thoughts?

The CRIUS seems to use the SSD1306. There are some differences (chargepump). I need to compare the datasheets in more detail. There are some hints here that the SSD1306 has an internal chargepump that needs to be activated. Your images will be too faint otherwise. Is that the case?

When bitmaps show the problem must be minor. Maybe the font table (font8x8.h) is somehow empty. Did you include the SSD1308 lib or did you include the source files and recompile with your own code.Have you tried writeChar() to display a single 8x8 character. Have you tried writeBigChar() to display a single large 16x24 digit. You may have seen my example program. That has a simple menu to test different functions.

I dont suspect the chargpump to be a problem, I can see images on the oled. I will however check out that link.

I imported your example ("An example programme is here") and I am using the same files. I checked to see if the 8x8.h was bad. First I created a new font8x8.h but nothing. Then I wanted to test if the 8x8 was in fact bad. So I changed the writeBigChar() to use the 8x8font. That worked fine. option 'E' displayed in 8x8 just fine.

It seems to me that the writeString() function is the problem. I am investigating the code but to be honest, I am new to OLED/GUI. The most display work I have done has been in 16x2 & 20x4 text.

I wrote a simple 'for loop' to increment the row/column portion. I was thinking maybe the cursor position was wrong, but nothing.

     
     while (1) {

     for(x = 0; x< 128; x++){
          writeString(x, y, "Hello World");
          pc.printf("cursor = (%d,%d)\n", x, y);
          }
     if(y<64); {
          x = 0;
          y++;
          }
     else
          pc.printf("end test");
}

I also wrote a simple main program with only the writeString(0, 0, "Hello World"); function.. no display

I will try writeChar() and also investigate the SSD1306

Thanks for your help, hopefully its something simple, I want to get the writeString() function working.

Hi Nicolas, just wondering if you had found the problem with the SSD1306. Looks like the difference between the SSD1308 and SSD1306 is that SSD1306 has an onboard chargepump. However, both devices can work with an external powersupply also and you should not activate the chargepump for the SSD1306 in that case.

There is one other issue that you may run into when using the I2C interface. The SSD1306 has separate pins for SDAin and SDAout. The SDAin is used to receive commands and data. The SDAout pin is used to Acknowledge the I2C commands or data to the host CPU (in this case mbed). The reasons for using separate pins are technical and I wont go into that here. Normally both pins are connected. However, in some cases the SDAout is NOT connected. That means the device will not acknowledge I2C traffic. The problem is now that the mbed I2C libs for blockwrite operations will abort when the I2C messages dont get an acknowledge. I my lib I use blockwrites for displaying a character. This happens in _sendData().

/** @brief Write databyte to display
 *  @brief Start at current cursor location
 *  @param uint8_t data databyte to write
*/
void SSD1308::_sendData(uint8_t data){

  char databytes[2];
    
  databytes[0] = DATA_MODE;
  databytes[1] = data;    
  _i2c.write(_writeOpcode, databytes, 2);    // Write Data   
  
}

So you may want to try replacing the blockwrite by separate I2C write operations. They still dont get acknowledged, but they will continue just the same.

Try this:

/** @brief Write databyte to display
 *  @brief Start at current cursor location
 *  @param uint8_t data databyte to write
*/

void SSD1308::_sendData(uint8_t data){

#if(0)
//I2C Blockwrite versions dont seem to work ?
//That may be related to fact that the SSD1306 does NOT return an acknowledge: blockwrite may abort the operation
//Noted for mbed lib v63 on 20/7/13 
  char databytes[2];
    
  databytes[0] = DATA_MODE;
  databytes[1] = data;    
  _i2c.write(_writeOpcode, databytes, 2);    // Write Data   

#else
  _i2c.start();
  _i2c.write(_writeOpcode);
  _i2c.write(DATA_MODE);  
  _i2c.write(data); 
  _i2c.stop();  
#endif
 
}

I dont see the Ack problem for my SSD1308, but that may be because it is wired differently. In my case both blockwrite and single writes work fine.

The latest mbed libs have made some changes that resulted in a "NoneCopyable" problem for the i2c bus parameter. The issue should be fixed in the new release of the SSD1308 lib. I have used the same method as in some of my other libs. You now need to instantiate the display as follows:

...
//Pin Defines for I2C Bus
#define D_SDA                  p28
#define D_SCL                  p27
I2C i2c(D_SDA, D_SCL);

// Instantiate OLED
SSD1308 oled = SSD1308(&i2c, SSD1308_SA0);

...