STM8 Microcontrollers – the Final Chapters

Hardware

Capacitive Touch Overview

Electronics and embedded-systems advancing fast. Designers and users are moving toward electronic solutions over mechanical ones. Touch screens, touchpads and touch switches are getting popular like never before and are replacing traditional mechanical switches, knobs, etc. ST like many other microcontroller manufacturers have provided resources for implementing capacitive touch buttons. However, the algorithm for implementing reliable capacitive touch sensors is a bit complicated especially when it comes to an 8-bit microcontroller. For this reason, ST has provided capacitive touch libraries for its STM8 and STM32 product line. These libraries along with SPL enable us to quickly and effectively add capacitive touch functionality in our designs.

Capacitive Touch

In STM8s, RC acquisition principle is used to implement capacitive touch sensors. No special hardware is required for implementing RC-based capacitive touch buttons/sliders/wheels. Just timers and GPIOs are all that are needed to get the job done. RC acquisition method detects a human touch on a capacitive touch sensor (acquisition pin/pins) by measuring small variations of the touch electrode’s capacitance. Capacitance exists between acquisition electrodes and ground. The touch electrode capacitance is periodically charged and discharged through a fixed resistor called load resistor by altering the logic state of the load I/O. A touch electrode’s capacitance depends on its area, relative dielectric constant of the insulator in-between, the relative permittivity of air and the distance between the two electrodes. Additionally, an active shield is used to get rid of parasitic capacitance between touch electrode(s) and ground. Parasitic capacitances originate due to environmental effects and other foreign objects. An active shield surrounds touch electrode(s) and maintain same in-phase potential. This leads to zero potential difference between the electrode(s) and shield, and thereby no parasitic capacitance builds up.

ST’s application note AN2927 details capacitive touch sensing.

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25 comments

  • Hey; thanks a lot for your prefect article, could you send me please the delay libraries I haven’t got the right version of them, I have an error about “delay_cycle()”.

    • STM8S_delay.h


      #include "stm8s.h"

      #define F_CPU 16000000UL
      #define dly_const (F_CPU / 16000000.0F)

      void delay_us(unsigned int value);
      void delay_ms(unsigned int value);

      STM8S_delay.c


      #include "stm8s_delay.h"

      void delay_us(unsigned int value)
      {
      register unsigned int loops = (dly_const * value) ;

      while(loops)
      {
      _asm ("nop");
      loops--;
      };
      }

      void delay_ms(unsigned int value)
      {
      while(value)
      {
      delay_us(1000);
      value--;
      };
      }

      I didn’t use delay cycle in my library…. Are you using some other compiler other than Cosmic + STVD?

  • Really outstanding library! Thanks for helping out. I am using the STM8AF5288 so made some changes and worked like a charm. but the issue i am facing right now is the font size. is there any available font library that could be replaced to get bigger fonts? and If possible can you explain how the font is being created on the ssd1306, I mean the way the pixels are being drawn using the hex code (in the font.h file).
    Thanks in advance.

  • Really outstanding library! Thanks for helping out. I am using the STM8AF5288 so made some changes and worked like a charm. but the issue i am facing right now is the font size. is there any available font library that could be replaced to get bigger fonts ? and If possible can you explain how the font is being created on the ssd1306, I mean the way the pixels are being drawn using the hex code (in the font.h file).
    Thanks in advance.

    • There are several OLED libraries available in the internet with big fonts but I’m happy with this font size to make maximum use of the display…. Thus I didn’t go for development of libraries with big fonts….

      • thanks for the quick reply, But the thing is that i am facing a issue with that of the draw bitmap function.
        i.e.
        void OLED_draw_bitmap(unsigned char xb, unsigned char yb, unsigned char xe, unsigned char ye, unsigned char *bmp_img)

        {

        unsigned int s = 0x0000;

        unsigned char x_pos = 0x00;

        unsigned char y_pos = 0x00;

        for(y_pos = yb; y_pos <= ye; y_pos++)

        {

        OLED_gotoxy(xb, y_pos);

        for(x_pos = xb; x_pos < xe; x_pos++)

        {

        OLED_write(bmp_img[s++], DAT);

        }

        }

        }

        and i am calling it by the following way:
        OLED_draw_bitmap(0,0,128,64,(unsigned char *)&image_data_LesInv);

        and my bitmap file goes like this:
        static const uint8_t image_data_LesInv[128][64] = {
        // 'untitled', 128x64px
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0x7f, 0x3f, 0x3f, 0x3f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f,
        0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f,
        0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f,
        0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x3f, 0x3f, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0x01, 0x00, 0x00, 0x00, 0x00, 0xf8, 0xf8, 0xf8, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18,
        0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0xf8, 0xf8, 0xf8,
        0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8,
        0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x7f, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xf8, 0xf0, 0xe0, 0xe0, 0xe0, 0xe0, 0x00, 0x00, 0x00, 0x01, 0x07,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x1f,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0x1f, 0x0f, 0x07, 0x07, 0x07, 0x07, 0x00, 0x00, 0x00, 0x80, 0xe0,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0x80, 0x00, 0x00, 0x00, 0x00, 0x1f, 0x1f, 0x1f, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18,
        0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18,
        0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f,
        0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x00, 0x00, 0x00, 0x00, 0x00, 0xc0, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xfe, 0xfc, 0xfc, 0xfc, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8,
        0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8,
        0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8,
        0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xfc, 0xfc, 0xfe, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
        };

        ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
        but the issue is that my image does gets generated but it gets back to blank screen within a 500ms or so.
        can you please help with the same.

        • void OLED_draw_bitmap(unsigned char xb, unsigned char yb, unsigned char xe, unsigned char ye, unsigned char *bmp_img)
          {
          unsigned int s = 0x0000;
          unsigned char x_pos = 0x00;
          unsigned char y_pos = 0x00;

          for(y_pos = yb; y_pos <= ye; y_pos++)
          {
          OLED_gotoxy(xb, y_pos);
          for(x_pos = xb; x_pos < xe; x_pos++)
          {
          OLED_write(bmp_img[s++], DAT);
          }
          }
          }

          This was the original code but yours seems to be modified in the for loops…. Please recheck unless it is intentional….

          • both the loops are the same. I did not make any changes in the original code but the bitmap image seems to get printed on the screen but it gets instantly blank within 20ms.
            can you help me for the same.
            Thanks in advance.

          • Could you send me the whole code? I think there is an overflow somewhere….

  • Hello,
    How can i change the font size so i can support for example [92][12] ? Saw some libraries on the net but i am not sure if they are compatible with this code… or am i doing something wrong ? I tried manipulating the current one with some cycles within ” OLED_print_char ” also chaning 0x06 to 0x0C with a font library also tried creating fonts but i did not get the expected result. Can you give me some advice please ?
    Thank you for your time!

    • The coordinates of the OLED displays are mapped as multiples of 8-bits or 8 dots in both x and y directions. So just by changing x-coordinate values won’t result in larger fonts…. You must also take care of the y-coordinate too…. Take the example of the bitmap function:

      void OLED_draw_bitmap(unsigned char xb, unsigned char yb, unsigned char xe, unsigned char ye, unsigned char *bmp_img)
      {
      unsigned int s = 0x0000;
      unsigned char x_pos = 0x00;
      unsigned char y_pos = 0x00;

      for(y_pos = yb; y_pos <= ye; y_pos++)
      {
      OLED_gotoxy(xb, y_pos);
      for(x_pos = xb; x_pos < xe; x_pos++)
      {
      OLED_write(bmp_img[s], DAT);
      s++;
      }
      }
      }

      It takes care of the y-coordinate part once the x-coordinate points are filled up….

  • Hi great tutorial!
    Can you post code for interfacing external eeprom using i2c for stm8s003f3??

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  • Outstanding bro. Carry on. Wish your good luck.

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