Programming AVR I2C interface

I2C (also referred to IIC or TWI) is a widely used interface in embedded applications. Two wire bus initially was used by Philips and become a standard among chip vendors. I2C bus consists of two lines called Serial Data Line (SDA) and Serial Clock Line (SCL). Communication is relatively fast, and short distance mainly used to communicate between sensors, RTC, EEPROM, LCD. I2C protocol allows up to 128 devices connected to those two lines where each of them has a unique address. Communication between devices is master and slave based. Master generates a clock signal, initiates and terminates data transfer. From electrical point of view I2C devices use open drain (open collector) pins. In order to operate correctly SDA and SCL lines require pull up resistors. Typically 4.7kΩ resistors are… Continue reading

ADC on Atmega328. Part 2

After we’ve learned how to performs simple ADC conversions on AVR microcontroller we can move forward with more complex tasks. AVR ADC module has many useful features that make conversions more robust without occupying MCU resources. Imagine that we need to sample analog waveform or audio signal. It has to be done precisely at defined sampling frequency like 20kHz. The only way to do this correct is to use auto-triggering with exact time intervals. Why not to pass counting task to timer? Lets write Timer0 auto-triggered ADC conversions with ADC complete interrupt service routine. Continue reading