Playing music and tones using a piezo buzzer - library for AVR microcontrollers using timer interrupt | ATmega328

This is a library for playing monophonic music using PWM and a piezoelectric buzzer. Monophonic means it can play only one note at a time. Regardless, it can produce some nice music. Optionally a led can be made to blink with the music rhythm.

Apart from playing songs it can also be used for tone generation useful in projects where audio indicators are needed.

All you need is a 16-bit timer that can be one of the following: timer1, timer3 and timer4 (provided that the microcontroller has them) and an 1ms interval interrupt where to place the main function. This is needed because the notes must have a certain duration.

Playing music on a piezoelectric buzzer using PWM and a microcontroller

Colorspace conversion between RGB and HSL library code for AVR microcontrollers | ATmega328P

I had a project where I needed to crossfade RGB colors and I thought why not using the HSL color space instead of the RGB color space because with the HSL the code looks neater and the Hue (color), Saturation and Lightness can easily be modified to create all kinds of light effects.

Converting HSL to RGB

HSLtoRGB(hue, saturation, lightness, rgb[])

How to control RGB leds | RGB fader library for AVR ATmega328P

RGB leds are fun and because they can be used in many projects I have decided to make a library to easily crossfade the colors of one or multiple RGB leds.

To see this library used in a real project, check out this video Digital Clock With RGB Night Lamp & Spherical Shelf.

Crossfading an RGB led in the RGB colorspace

With 8 bits we have 256 values from 0 to 255 that represents the duty cycle - how long a led will be on then off in a period. For example setting the RED led to 255 and GREEN and BLUE to 0 will result in RED color. Or RED 255, GREEN 0 and BLUE 255 will show a purple color. All leds on (255 value) will result in a white lite. So this is how a certain color can be produced but how to cycle through all the possible combinations?

First the red color is set at 255 and green and blue to 0. Then the red will be decremented and the green will be incremented. When the red will be 0 and green 255 we change the fading up and fading down colors.

Multi-channel software PWM library for AVR microcontrollers | ATmega328P

What you do when you run out of PWM pins on hardware? You make software PWM of course. This library is based on "AVR136: Low-Jitter Multi-Channel Software PWM" application note. It supports up to 10 PWM channels (more can be added) and it's suitable for led dimming, DC motor control and RGB led controller.

Since this method is already explained in the AVR136 app note I won't go in to too many details. So the basic principles behind software PWM are this. A timer interrupt is set to trigger every 256 system clocks. For 8 bit timers the interrupt is on overflow and for 16 bit timers is on compare match. A 16 bit timer has the advantage that the base frequency can be modified. On every interrupt a variable "softcount" is incremented from 0 to 255 and each time is compared against each PWM channel. At the beginning of the cycle the pins are set high and when "softcount" equals to a channel's set value then the specific pin is set low. On 8MHz CPU the ISR takes between 4 and 10us to execute the code depending on how many channels and on how many ports there are. The size of the "softcount" variable dictates the PWM resolution and it is set to 8 bits.