ARM Cortex-M3 (STM32F103) Tutorial - SPI Master

In this tutorial, I will explain about SPI communication protocol and how to use it on STM32F103 microcontroller. SPI (Serial Peripheral Interface) is a synchronous serial communication protocol. With SPI, in addition to transmitting and receiving lines, there is a third line that used for clock line. Each slave devices also has a chip select (enable) pin. These pin is used for activate the slave devices. So, to use SPI, we need 2 wire for data lines (MOSI, MISO), 1 wire for clock line, and 1 wire per device for chip select line. MOSI (Master Out Slave In) is used for data transfer from master device to slave device. MISO (Master In Slave Out) is used for data transfer from slave device to master device.

SPI communication is different from other serial communication especially on data transfer. There are no concept like transmit and receive data, but there is a data trading concept. When data trading occurs, the data bits in master register is traded with the data bits in slave register on every clock from master (one data bit per clock tick).

ARM Cortex-M3 (STM32F103) Tutorial - LCD 16x2 Library

In this tutorial, I will share about LCD 16x2 library. With this library, you can easily use LCD 16x2 with STM32F103 microcontroller. This library contain 2 file: lcd16x2.h and lcd16x2.c files. If you want to know the more detail how the LCD 16x2 works, you can see this tutorial.

ARM Cortex-M3 (STM32F103) Tutorial - FreeRTOS - Task

In this tutorial, I will share how use an RTOS on STM32F103 microcontroller. I use FreeRTOS for this tutorial. RTOS is usually needs when an embedded system must responds to an event within a strictly defined time.

In this tutorial, I will make RTOS task with 3 LED that blinks at different frequency. First thing to do is to download FreeRTOS library. The next step is to make a new project in Keil uVision and setup the configuration for using FreeRTOS on STM32F103.

ARM Cortex-M3 (STM32F103) Tutorial - I2C Master

In this tutorial, I will explain about I2C protocol and how to use it on STM32F103 microcontroller. I2C (Inter-Integrated Circuit) or sometimes called TWI (Two Wire Interface) is a synchronous serial protocol that only need 2 wire for communication. These wire are SCL for clock line and SDA for data line. Using I2C bus, you can connect devices like temperature sensor, EEPROM, RTC, etc (up to 112 device) just using two wire (plus GND wire). For accessing these device, I2C use 7-bit address. Theoretically 7-bit address space allows 128 addresses, however some addresses are reserved for special purpose. Thus, only 112 address can be used. There is also special method to use I2C with 10-bit address.

I2C is multi-master and multi-slave bus. I2C bus can consists of one or more master device, but only one master device can have an access to I2C bus each time. To communicate with a slave device, master is responsible for sending clock to the slave device. Clock signal is always generated by master. I2C drivers are open-drain, means that they can pull the signal low, but can't drive it high. On each signal line (SCL and SDA) must have a pull-up resistor to restore the signal high when no device is asserting it low.

ARM Cortex-M3 (STM32F103) Tutorial - 4x4 Matrix Keypad

Embedded system applications usually require large number of buttons connected (ex. calculator, cell phone). Keypad is one of the input device that commonly used in embedded system that require large number of buttons. 4x4 matrix keypad have 16 buttons. We can connect this buttons directly to GPIO pin, but it will eat up precious GPIO pin (If we have 16 buttons, then we need 16 GPIO pins). To avoid this trouble, keypad use technique that will save GPIO pin. In this technique, buttons are connected in a matrix (row/column) style.

The internal connection of the buttons in 4x4 matrix keypad is like this:

ARM Cortex-M3 (STM32F103) Tutorial - Unipolar Stepper Motor

In this tutorial, I will share how control a unipolar stepper motor using STM32F103 microcontroller. If you don't know the basic of the stepper motor, I suggest you to read this article first. To control a stepper motor from microcontroller, we can't directly drive it with GPIO pins because GPIO pins have maximum current that can sink or source from it. To overcome this problem, we can use driver circuit. The driver circuit for unipolar stepper motor can be built by using 4 transistors to drive large current every 4 wires of a stepper motor. It also can be built with ULN2003 IC. This is the circuit for driving a unipolar stepper motor from microcontroller by using ULN2003 IC:

In this tutorial, I will use 28BYJ-48 stepper motor. This motor is very cheap and it also comes with driver module based on ULN2003 IC. This motor runs with 5V supply and has gear inside. The gear reduction ratio is approximately 64:1. If you search from internet, other people say that the gear reduction ratio is actually 63.68395:1.