How to display " °C " in OLED Display for STM32 IDE?

Question

I am unable to display the symbol for degree celsius in my display, is there anyway to do it other than drawing a circle manually?

I tried giving the "char ASCII code" for some symbols to check whether my OLED could do it. It can display symbols for tilda etc, but I dint find a way to display the degree symbol. Is there any other way other than doing it manually?

This is my SSD1306 source library.

https://gist.github.com/akx/bc563420a8950443e5490c5ba14eb876#file-ssd1306-c-L604-L608

Answer 1

The problem with ° is that it's not an ASCII character, but an extended ASCII character (its code is 0xB0 - number 176 - above 127). It could be that your library only implements the standard 127 ASCII characters.

Drawing custom patterns on SSD1306 is not really hard, and it takes only a few minutes of experiments to figure it out. If you draw a single byte of 0xFF, it will draw a straight horizontal line of pixels. After all, it's a monochrome screen, so 1 bit is 1 pixel. On or off. Of course, for something like ° you could just have a function that would take a starting pixel or cursor position and print a space character, then call your custom code to draw a small circle over it.
This approach is meh because you can't just print a string with it. But if it's for some static interface, it's more than enough. I used this approach to draw a battery level indicator - just a couple of custom bitmaps in the fixed location of the screen.

Maybe you could "hack" into the library and either add your custom bitmap of the symbol and associate it with a character code (if it permits codes >127), or replace one of the less useful (for your application) printable symbols of basic ASCII with °. For example, $ or ~. So in your code you will write something like screen.print("Temperature is 25$C");, and the screen will show Temperature is 25°C.

A quick glance at the library you linked to reveals that there exists a "font object" in functions that are supposed to print text (they take pointer to font object as one of the inputs). That's where you should probably start looking, if you want to go down this road.