Wednesday, April 21, 2021

Building a Digital Clock with RGB Lamp & Spherical Shelf DIY

Here is how to build a simple digital wall clock encased in a spherical shelf that could make a nice gift for someone.

The clock is based on an ATmega328PB microcontroller that is using a 32.768 kHz crystal for time keeping. It also has 6 RGB leds that act as a night lamp or simply for aesthetic purposes.

Digital Clock With RGB Lamp & Spherical Shelf DIY

Thursday, February 25, 2021

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 and tones using a piezo buzzer - library for AVR microcontrollers using timer interrupt | ATmega328P, ATmega88

Playing music on a piezoelectric buzzer using PWM and a microcontroller


Saturday, February 6, 2021

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.

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

Converting HSL to RGB

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

Thursday, February 4, 2021

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.

How to control RGB leds | Crossfading RGB leds | Library for AVR ATmega328P

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?

Crossfading an RGB led in the RGB colorspace 1

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.

Wednesday, February 3, 2021

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.

Multi-channel software PWM library for AVR microcontrollers | ATmega328P

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. 

Saturday, January 23, 2021

Binary Code Modulation (BCM) aka Bit Angle Modulation (BAM) library for fading leds for AVR microcontrollers

Binary Code Modulation (BCM) was invented by Artistic Licence and is a form of PWM but not really. The main advantage over software PWM is the low CPU usage regardless of how many channels it controls.

This library provides a fast implementation of Binary Code Modulation useful for controlling RGB leds and dimming multiple leds for creating animations like led cubes and includes an array for logarithmic brightness. A complete cycle takes 8 timer interrupts and each interrupt takes only 4us on a 8MHz CPU. The leds can be on different ports.

Bit Code Modulation (BCM) aka Bit Angle Modulation (BAM) library for RGB led dimming - 8-bit

How Binary Code Modulation (BCM) works and how it differs from PWM

To dim a led with PMW is simple. If you want the led to be half as bright you turn the led on for 50% of the cycle and 50% for the other half. Or 20% on and 80% off for an even dimmer led.

 

PWM example

Bit Angle Modulation uses the weight of each bit in a binary number. For example in one byte there are 8 bits with numbers from 0 to 7. Bit 0 is called the Least Significant Bit (LSB) and it's weight is 1. Next bit 1 has a weight of 2, bit 2 has a weight of 4, then 8, 16, 32, 64 and 128. Bit 7 is called the Most Significant Bit (MSB) because it has the highest weight - 128.

8-bit binary weight

Monday, January 18, 2021

7 segment display library for AVR microcontrollers | ATmega328P

There are many ways to control a seven segment display - using a dedicated IC or shift registers which are preferred because they don't require many pins. However this library is made for when you have the segments driven directly from microcontroller pins and each digit is controlled using a transistor.

You have the option of padding the numbers with zeros and displaying them at a certain position, useful for making digital clocks.

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

Seven segment display library for AVR microcontrollers

What is a 7-segment display

As the name suggests it is a display that is made up of 7 segments. Each segment is simply an LED. Including the dot there are actually 8 LEDs and this fits perfectly on an 8-bit microcontroller's port. This display is mainly made for numerical values but some alphabetical characters can be displayed as well.

Types of 7 segment displays

There are two types of seven segment displays - common cathode and common anode. Common cathode displays have all the ground sides (cathodes) of the LEDs connected together while common anode displays have all the positive sides (anodes) of LEDs tied together.

The 7 segment display can have from 1 up to 6 or 8 digits. One digit can display numbers from 0 to 9 and a dot for numbers with decimals. On 4 digit seven segment display the maximum number that can be displayed is 9999.

7 segment display internal equivalent circuit OPD-Q5621LE-BW
Figure 1: Internal equivalent circuit of a 7 segment display from OPD-Q5621LE-BW datasheet