C Library for SSD1306 OLED Display and ATtiny85

C Library for SSD1306 OLED Display and ATtiny85

It isn’t hard to get one of those OLED displays from eBay or another place. They are usually controlled by SSD1306 chip – one of the most popular. Such displays could be used for a number of things – from just learning to control them and showing some text/numbers/graphics, display sensors’ data or even creating a small game.

SSD1306 OLED Display
SSD1306 OLED Display

Back in 2014, we wrote a small library for the ATtiny85 microcontroller to work with such displays and we called it SSD1306xLED after the name of the controlling chip for the display.

Here is a link to check what’s for sale now:
http://www.ebay.com / OLED 128 64

IMPORTANT DISCLAIMERS:

  1. This library works with the display modules that use the I2C protocol. This is important to know since there are other similar displays that use the same SSD1306 controller but communicate over the SPI interface. In that case, our library will not work. We use, in most cases, the modules with 4 pins – GND, Vcc, SCL, SDA.
  2. Although using the I2C interface, our SSD1306xLED library does not implement the I2C protocol but just a subset of it enough to accomplish the task of sending commands and data to the display. This comes with 2 great advantages: (1) it is super fast; (2) is super small – more details about those characteristics will be outlined below.

The library is, of course, open source and all the software is available at https://bitbucket.org/tinusaur/ssd1306xled/

The I2CSW sub-library

This is a small sub-library that implements a subset of the I2C protocols that is necessary to send some commands and data out. I2CSW stands for “I2C Simple Writer” and as its name implies it only writes out.

There are 2 macros to sent the SCL and SDA wires to high and to low, or, or 1 and 0.
I2CSW_HIGH(PORT)
I2CSW_LOW(PORT)

Then, there are 3 low-level functions:
— void i2csw_start(void);
— void i2csw_stop(void);
— void i2csw_byte(uint8_t byte);

The i2csw_start function sets the SCL and SDA pins as output and the “start” condition. In other words, it lets the devices connected to the microcontroller know that we are about to send something out.

The i2csw_stop function sets the “stop” condition. This indicates that we have finished with sending the data. It also set the SDA pin as input so it won’t keep the SDA line at HIGH all the time.

SSD1306 I2C Start and Stop Condition
SSD1306 I2C Start and Stop Condition

The i2csw_byte function sends one byte of data out. It is used to send commands and data to the I2C devices – the display in our case.

SSD1306 I2C Acknowledgment Condition
SSD1306 I2C Acknowledgment Condition

NOTE: The I2CSW library does not handle the acknowledgment condition.

The ssd1306 core functions

There are 4 core functions in the library at the moment:
— void ssd1306_start_command(void);
— void ssd1306_start_data(void);
— void ssd1306_data_byte(uint8_t);
— void ssd1306_stop(void);

The ssd1306_start_command function indicates to the connected I2C devices that we’re about to send commands. This is used to configure the controller o to set some parameters such as the current position on the display.

The ssd1306_start_data function indicates to the connected I2C devices that we’re about to send some data. This is used to send some data to the display controller – like bitmaps or text.

The ssd1306_data_byte function sends 2 bytes of data to the display controller. That is used for both commands and data.

The ssd1306_stop function indicates that we have finished transmitting data.

SSD1306 I2C Write data
SSD1306 I2C Write data

The ssd1306 supplementary functions

These are convenience functions:
— void ssd1306_init(void);
— void ssd1306_setpos(uint8_t x, uint8_t y);
— void ssd1306_fill4(uint8_t, uint8_t, uint8_t, uint8_t);

The ssd1306_init function sends a sequence of commands that will initialize the display controller so it will work the way we expect.

The ssd1306_setpos function sets the current position on the display. Sending data after this command will display it at that position.

From the documentation:

Horizontal addressing mode (A[1:0]=00b)

In horizontal addressing mode, after the display RAM is read/written, the column address pointer is increased automatically by 1. If the column address pointer reaches column end address, the column address pointer is reset to column start address and page address pointer is increased by 1. The sequence of movement of the page and column address point for horizontal addressing mode is shown in Figure 10-3. When both column and page address pointers reach the end address, the pointers are reset to column start address and page start address (Dotted line in Figure 10-3.)

Solomon Systech Apr 2008 P 42/59 Rev 1.1 SSD1306
SSD1306 I2C Horizontal addressing mode
SSD1306 I2C Horizontal addressing mode

The ssd1306_fill4 function fills out the screen with the 4 bytes specified as parameters. The reason for 4 bytes is that it is convenient for filling out with patterns.

There are 3 other functions derived from the ssd1306_fill4 function:
ssd1306_clear() – clears the screen, i.e. fills it out with “0”.
ssd1306_fill(p) – fills the display with the specified byte.
ssd1306_fill2(p1, p2) – fills the display with the 2 specified bytes.

The testing scripts demonstrate the purpose and usage of those functions.

The testing in the “ssd1306xled_test1” folder

Source code at https://bitbucket.org/tinusaur/ssd1306xled/src/default/ssd1306xled_test1/main.c

This testing script demonstrates the use of the functions in the library.

The first section fills out the screen with random values using a Linear congruential generator.

SSD1306 Library SSD1306xLED Testing Script
SSD1306 Library SSD1306xLED Testing Script

The second section fills out the screen with a sequential number that creates some patterns on the screen.

SSD1306 Library SSD1306xLED Testing Script
SSD1306 Library SSD1306xLED Testing Script

The next section fills out the screen line by line.

SSD1306 Library SSD1306xLED Testing Script
SSD1306 Library SSD1306xLED Testing Script

The last section fills out the screen with various patterns.

More functions …

There are more functions in the SSD1306xLED library such as for printing text and numbers on the screen and drawing images but that will be subject of another article.

Please, share your thoughts!

The Tinusaur team was at the BETT Show in London

Meet Tinusaur team at BETT show London ExCeL

The Tinusaur Project is an educational platform that provides students, teachers, and makers with the tools to learn, teach and make things. We’ve been developing this since 2013 and it started because we needed such tools for our own courses. It is now used in a few schools and universities, both private and government in Bulgaria. The education, whether formal or informal, has always been the focus of the Tinusaur. Naturally, the BETT Show in London is one of the most interesting events of the year in that field.

BETT Show in London
BETT Show in London

The BETT Show is an annual trade show focused on innovations and technology in education. It takes place in London, United Kingdom, and started in 1985.

BETT Show in London
BETT Show in London – Learning Robotics

The Tinusaur team is at the BETT Show, of course, for the second time and it is great here!

BETT Show in London
BETT Show in London – Learning Robotics

What you immediately notice is that everyone has some sort of a robot – a car that you could control to make movements based on an algorithm, or a human-like stumping robot. And those who don’t have a robot – have at least a snapping blocks with electronics like LEDs, motors, servos, etc. that you could program with a Scratch-like environment. This sort of toys becomes a standard for education in electronics, robotics, and programming.

BETT Show in London
BETT Show in London – “Real” Robot

To us, this is a bit disconcerting. Most of those products turn education into a game or playing. Gamification is not just creating a game with which you might (or might no) learn something. It is rather implying the using of game-design elements to improve the process of learning without compromising the process of acquiring knowledge. Another concern that we have is that once you’re done with the playing and you have accomplished the task part of the educational toy you have to put it away and that’s it – you cannot use it to create something useful and practical.

BETT Show in London
BETT Show in London – Learning Robotics

We, at Tinusaur, are trying to avoid the downgrading of the educational part. That is why our kits may look a bit difficult and tedious at first. For the same reason, we decided to focus on C language programming, instead of some other scripting language.

Blocktinu WebUI
Blocktinu WebUI

Another thing we’re trying to do is make the kits equally good for learning and making. We think this is what makes us different. Our goal, from the very beginning, has been to create a platform where everything you learn and create could be used at a later point for something real, useful and practical. And over the years we found out that students really appreciate that.

Tinusaur OLED Display Кit
Tinusaur OLED Display Кit

The Tinusaur OLED Display Kit is a very good example for that.

  • You learn how to solder and assemble the boards and the modules.
  • You learn how to program the microcontroller, read the sensor data and visualize it on the display.
  • You could later use the boards and optionally add other sensors and create something that you could use at home.
  • Your imagination is the limit.

We have just launched a crowdfunding campaign for the Tinusaur OLED Kit.

Help us start the production of the Tinusaur OLED boards. Go get your own Tinusaur OLED Kit.

Launched crowdfunding campaign for the Tinusaur OLED Display Kit

Tinusaur OLED Display Кit

We have just launched our crowdfunding campaign at Crowd Supply for the Tinusaur OLED Display Kit – a bundle of boards and modules that allows you to connect an ATtiny85 microcontroller to an SSD1306 OLED display. This is a kit so you have to assemble the boards yourself by soldering the parts to the PCB thus start learning about electronics and physics. It might sound complicated at first but these Tinusaur boards are very easy to assemble using the guides and tutorials that we provide. Once all the boards are assembled you could connect a DHT11 sensor module, measure temperature and humidity and show the results on the screen.

Tinusaur OLED Display Кit
Tinusaur OLED Display Кit

With the Tinusaur OLED Display Kit, you get everything you need to start: the Tinusaur main board with the ATtiny85 microcontroller, the LED shield for test and learning, the OLED display shield, the SSD1306 OLED display, the DHT11 sensor module, a LiPo battery kit, and, a USBasp programmer.

The Tinusaur is an Open Source project – both the software and the hardware. Our own library for with the display, called SSD1306xLED, is considered one of the fastest for that display and microcontroller.

Check out the campaign page for details!

Launching Crowdfunding Campaign in January

Tinusaur OLED SSD1306xLED Crowdfunding Campaign

It looks like that our most popular software library is the SSD1306xLED. This is a library for working with OLED displays based on the SSD1306 controller. So, we decided to create a Tinusaur shield to carry an OLED display and we’re thinking about putting it up for crowdfunding this January.

What could you do it a Tinusaur Board and an OLED display?

There is an internal temperature sensor built into the ATtiny85 microcontroller and you don’t need any external components to use it. You can read its value and show it on the display.

Tinusaur OLED SSD1306xLED
Tinusaur OLED SSD1306xLED measuring temperature and voltage

We’ve figured a way to measure the battery level (or the power supply voltage) connected to the ATtiny85 microcontroller by using the PB5 (that is the RESET pin, yes) and one additional resistor. It is not very precise but could give you an indication, at least.

DHT11 module
DHT11 Module

You could also connect one of those popular DHT11 sensor modules, measure temperature and humidity and show it on the screen.

BM180 module
BM180 Module

You could also connect the Bosch BMP180 sensor module and measure barometric pressure and temperature, and show it on the screen. That will also allow you to calculate the altitude – pretty neat, isn’t it?

The official announcement with information about the start date, goals and other details is coming up in early January.

Printing Decimal Numbers on SSD1306 OLED Display Using the SSD1306xLED Library

Tinusaur SSD1306XLED SSD1306 OLED Llibary

After playing for awhile with that SSD1306 OLED display I decided to add few more things to the SSD1306xLED library and the ability to print numbers seamed to be an important one.

Tinusaur SSD1306xLED ATtiny85 SSD1306 OLDEThere is already a function in the library that outputs strings so I needed only the conversion from int to decimal string. So I used another function usint2decascii that I previously wrote for another project OWOWOD which code in turn I borrowed from a third project LCDDDD – a LCD Direct Drawing Driver for PCD8544 based displays such as Nokia 3310 LCD. The weird LCDDDD name comes from the fact that it outputs the data directly to the LCD instead of storing it into a buffer first and then periodically outputting it to the LCD – this is unlike most of the popular LCD drivers.

Here is the main function definition …

uint8_t usint2decascii(uint16_t num, char* buffer)

The function requires a small buffer to store the result. Since the largest number is 65535 – that is 0xFFFF in hex, 5+1 bytes are needed for that buffer.

For convenience there are 2 functions for direct printing of numbers. Below is their implementation – it’s very simple:

#define USINT2DECASCII_MAX_DIGITS 5

char ssd1306_numdec_buffer[USINT2DECASCII_MAX_DIGITS + 1];

void ssd1306_numdec_font6x8(uint16_t num) {
  ssd1306_numdec_buffer[USINT2DECASCII_MAX_DIGITS] = '\0';
  uint8_t digits = usint2decascii(num, ssd1306_numdec_buffer);
  ssd1306_string_font6x8(ssd1306_numdec_buffer + digits);
}

void ssd1306_numdecp_font6x8(uint16_t num) {
  ssd1306_numdec_buffer[USINT2DECASCII_MAX_DIGITS] = '\0';
  usint2decascii(num, ssd1306_numdec_buffer);
  ssd1306_string_font6x8(ssd1306_numdec_buffer);
}

The ssd1306_numdec_font6x8 only prints the number while ssd1306_numdecp_font6x8 prints numbers the same way but right-aligned and 5-digit padded.

Printing numbers is as simple as this …

  ssd1306_setpos(20, 4);
  ssd1306_numdecp_font6x8(12345);

Here is a little more complicated example …

ssd1306_setpos(40, 3);
ssd1306_string_font6x8("a=");
ssd1306_numdecp_font6x8(0xFA32); // dec: 64050
ssd1306_setpos(40, 4);
ssd1306_string_font6x8("b=");
ssd1306_numdecp_font6x8(0x05CD); // dec: 1485

ssd1306xled sample screen

It prints “a=”, “b=” and then their values. Both numbers are right-aligned and left-padded with up to 4 spaces.

The latest test program in SSD1306xLED includes examples of how to use the ssd1306_numdec_font6x8 and the ssd1306_numdecp_font6x8 functions.

The SSD1306xLED library is at SSD1306xLED page.

Source code of the SSD1306xLED is available at https://bitbucket.org/tinusaur/ssd1306xled

Source code of the TinyAVRLib is available at https://bitbucket.org/tinusaur/tinyavrlib

C Library for ATtiny85 to Work with SSD1306 Controlled OLED Display

I recently bought an OLED display 128×64 from eBay (http://www.ebay.com/sch/i.html?_nkw=OLED+128) – very inexpensive (about 4 euro) but when I finally received it I was surprised to see how small it was – I was expecting something that looked more like the Nokia 3310 LCD. So I thought – this is perfect for the Tinusaur Project. The 128×64 OLED is controlled by a SSD1306 circuit and could be interfaced over I²C. The first challenge that I faced was that all existing libraries that I found were for Arduino boards … and I wrote my own based, of course, on existing code – the SSD1306xLED library.

SSD1306xLED library for OLED/PLED 128x64

SSD1306xLED is a C library for working with the SSD1306 display driver to control dot matrix OLED/PLED 128×64 displays. It is intended to be used with the Tinusaur board but should also work with any other board based on ATtiny85 or similar microcontroller – ATtiny45/ATtiny25, even ATtiny13.

The code could be divided in 3 pieces: (1) communication over I²C with the SSD1306; (2) sending graphical commands to the display; (3) high-level functions such as printing characters.

The I²C communication part is based on modified IIC_wtihout_ACK library that is available on the Internet but its original website (http://www.14blog.com/archives/1358) is no longer functional. Basically, it made it to work on ATtiny85 and Tinusaur.

The SSD1306xLED library still needs work and improvements.

The main location for the library is SSD1306xLED page.

The source code along with very simple example is available on Bitbucket at this address: https://bitbucket.org/tinusaur/ssd1306xled