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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.

Meet the Tinusaur team at the FOSDEM in Brussels, Belgium

Tinusaur Team at FOSDEM

We are launching a crowdfunding campaign for the Tinusaur OLED Display Kit and this its page: https://www.crowdsupply.com/tinusaur/oled-display-kit


Meet the Tinusaur team at the FOSDEM in Brussels, Belgium on February 2nd and 3rd.

Would you like to contact us and meet at the event or have a question about our platform? Fill out the form below.


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!

Interfacing a MAX7219 Driven LED Matrix with ATtiny85

LED Matrix 8x8 MAX7219 Assembling

The MAX7219 controller is manufactured by Maxim Integrated is compact, serial input/output common-cathode display driver that could interface microcontrollers to 64 individual LEDs, 7-segment numeric LED displays of up to 8 digits, bar-graph displays, etc. Included on-chip are a BCD code-B decoder, multiplex scan circuitry, segment and digit drivers and an 8×8 static RAM that stores each digit. 

The MAX7219 modules are very convenient to use with microcontrollers such as ATtiny85, or, in our case the Tinusaur Board.

The Hardware

The MAX7219 modules usually look like this:

MAX7219 Module LED Matrix 8x8
MAX7219 Module and LED Matrix 8×8

They have an input bus on one side and output bus on the other. This allows you to daisy chain 2 or more modules, i.e. one after another, to create more complicated setups.

The modules that we are using are capable of connecting in a chain using 5 small jumpers. See the picture below.

MAX7219 Module LED Matrix 8x8
2x MAX7219 Modules Connected

Pinout and Signals

MAX7219 module has 5 pins:

  • VCC – power (+)
  • GND – ground (-)
  • DIN – Data input
  • CS – Chip select
  • CLK – Clock

That means that we need 3 pins on the ATtiny85 microcontroller side to control the module. Those will be:

  • PB0 – connected to the CLK
  • PB1 – connected to the CS
  • PB2 – connected to the DIN

This is sufficient to connect to the MAX7219 module and program it.

The Protocol

Communicating with the MAX7219 is relatively easy – it uses a synchronous protocol which means that for every data bit we send there is a clock cycle that signifies the presence of that data bit.

MAX7219 Timing Diagram
MAX7219 Timing Diagram

In other words, we send 2 parallel sequences to bits – one for the clock and another for the data. This is what the software does.

The Software

The way this MAX7219 module works is this:

  • We write bytes to its internal register.
  • MAX7219 interprets the data.
  • MAX7219 controls the LEDs in the matrix.

That also means that we don’t have to circle through the array of LEDs all the time in order to light them up – the MAX7219 controller takes care of that. It could also manage the intensity of the LEDs.

So, to use the MAX7219 modules in a convenient way we need a library of functions to serve that purpose.

First, we need some basic functions in order to write to the MAX7219 registers.

  • Writing a byte to the MAX7219.
  • Writing a word (2 bytes) to the MAX7219.

The function that writes one byte to the controller looks like this:

void max7219_byte(uint8_t data) {
    for(uint8_t i = 8; i >= 1; i--) {
        PORTB &= ~(1 << MAX7219_CLK);   // Set CLK to LOW
        if (data & 0x80)                // Mask the MSB of the data
            PORTB |= (1 << MAX7219_DIN);    // Set DIN to HIGH
        else
            PORTB &= ~(1 << MAX7219_DIN);   // Set DIN to LOW
        PORTB |= (1 << MAX7219_CLK);        // Set CLK to HIGH
        data <<= 1;                     // Shift to the left
    }
}

Now that we can send bytes to the MAX7219 we can start sending commands. This is done by sending 2 byes – 1st for the address of the internal register and the 2nd for the data we’d like to send.

There is more than a dozen of register in the MAX7219 controller.

MAX7219 Registers and Commands
MAX7219 Registers and Commands

Sending a command, or a word, is basically sending 2 consecutive bytes. The function implementing that is very simple.

void max7219_word(uint8_t address, uint8_t data) {
    PORTB &= ~(1 << MAX7219_CS);    // Set CS to LOW
    max7219_byte(address);          // Sending the address
    max7219_byte(data);             // Sending the data
    PORTB |= (1 << MAX7219_CS);     // Set CS to HIGH
    PORTB &= ~(1 << MAX7219_CLK);   // Set CLK to LOW
}

It is important to note here the line where we bring the CS signal back to HIGH – this marks the end of the sequence – in this case, the end of the command. A similar technique is used when controlling more that one matrix connected in a chain.

Next step, before we start turning on and off the LEDs, is to initialize the MAX7219 controller. This is done by writing certain values to certain registers. For convenience, while coding it we could put the initialization sequence in an array.

uint8_t initseq[] = {
    0x09, 0x00, // Decode-Mode Register, 00 = No decode
    0x0a, 0x01, // Intensity Register, 0x00 .. 0x0f
    0x0b, 0x07, // Scan-Limit Register, 0x07 to show all lines
    0x0c, 0x01, // Shutdown Register, 0x01 = Normal Operation
    0x0f, 0x00, // Display-Test Register, 0x00 = Normal Operation
};

We just need to send the 5 commands above in a sequence as address/data pairs.

Next step – lighting up a row of LEDs.

This is very simple – we just write one command where 1st byte is the address (from 0 to 7) and the 2nd byte is the 8 bits representing the 8 LEDs in the row.

void max7219_row(uint8_t address, uint8_t data) {
    if (address >= 1 && address <= 8) max7219_word(address, data);
}

It is important to note that this will work for 1 matrix only. If we connect more matrices in a chain they will all show the same data. The reason for this is that after sending the command we bring the CS signal back to HIGH which causes all the MAX7219 controllers in the chain to latch and show whatever the last command was.

Testing

This is a simple testing program that lights up a LED on the first row (r=1) on the right-most position, then moves that on the left until it reaches the left-most position, then does the same on one row up (r=2) )until it reaches the top (r=8).

max7219_init();
for (;;) {
    for (uint8_t r = 1; r <= 8; r++) {
        uint8_t d = 1;
        for (uint8_t i = 9; i > 0; i--) {
            max7219_row(r, d);
            d = d << 1;
            _delay_ms(50);
        }
    }
}
MAX7219 Testing MAX7219LED8x8 Library
MAX7219 Testing

This testing code doesn’t do much but it demonstrates how to communicate with the MAX7219 controller.

The MAX7219LED8x8 Library

All of the functions mentioned above are part of the MAX7219LED8x8 library. Its source code is available at https://bitbucket.org/tinusaur/max7219led8x8.

The Tinusaur Shield GAMEx3

If you already have a Tinusaur Board we have the Shield GAMEx3 for it to connect a MAX7219 module easier to your ATtiny85 microcontroller.

Shield GAMEx3
Shield GAMEx3

The Gametinu Project

The Gametinu is a small game platform that you could build yourself using the Shield GAMEx3 and a few more parts and tools.

Gametinu
Gametinu

References

MAX7219 specification and datasheet:


This article is a rewritten version of another article from 2014:
MAX7219 driver for LED Matrix 8×8.


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.

The Blocktinu App for Windows version 1.2.1 is out

Blocktinu Windows App

We have just deployed new version of the Blocktinu Windows application.

It is available for download from BLOCKTINU.com/downloads website.

WHAT’S NEW?

Besides some visual changes, there is a new button to upload some testing code to your Tinusaur Board with an EDUx4IO Shield. That is very convenient for testing if the board was assembled correctly even before you start writing some code.

A more detailed guide on how to setup Blocktinu on Windows is available as a PDF file for download at Blocktinu Tools – Windows Setup (slides).pdf.

We’d like to hear your opinion, so please drop a comment.

Blocktinu Tools – Windows Setup (slides)

Blocktinu Tools - Windows Setup (slides)

This is the first draft of the guide how to setup the Blocktinu Tools under Windows.

Tinusaur Blocktinu Logo

The file in PDF format is available at this location: Blocktinu Tools – Windows Setup (slides).pdf

Please, download it and take a look. If you feel that there’s missing something or wrong, please, let us know.

When we update the files we will commit changes in this repository: https://bitbucket.org/tinusaur/blocktinu-docs/.

Check also the Guides section of our website.