Avr clock

Wall clock made of avr mcu and led display using internal timer

Idea

The main goal was to try numeric LED display with MCU, so to make it a little bit more interesting I decided to create a clock that shows time in digital and analogue way. I used Atmega16L MCU because I needed 26 I/O pins (12 for numeric display, 12 for 2mm LEDs and 2 for buttons). The clock has got two buttons - one for adding hours and one for minutes. 2mm LEDs around edge shows seconds while numeric display inside shows hours and minutes.

Display

I bought my display from ebay without any data sheet, but it is almost the same for all kinds of displays. You can easily find the right combination of pins. Four 7-segment digits are controlled via 12 I/O pins. Each digit is made of 8 parts (7 for number, 1 for dot). The other four pins are ground for each number. So to light up 4 different digits you have to toggle between all of them quickly.

Timers

A timer is a simple counter. The ATmega16 has two 8 bit and one 16 bit timer. The 8 bit counter (uses 8 registers) can count up to 2^8 = 255 while the 16 bit counter (uses 16 registers) can count up to 2^16 = 65 536. After reaching the maximum value for counter it simply overflows back to zero.

Lets say the MCU works on 1MHz frequency, that means it does 1 000 000 ticks per second, but the counters can only count up to 255 (8 bit timer) or 65 536 (16 bit timer) then it overflows. To set the counter properly you have to set the limit (prescaler) and also setup bits for right mode. All of the necessary configuration can be found in data sheet.

I used 16 bit timer with CTC mode (clear time on compare - when reached predefined value it is automatically set back to zero) with external interruption. The main thread is used for logic and redrawing while second thread (external interrupt) is used for counting time. There is a nice youtube tutorial for avr timers and also a avr timer calculator can be handy.

Result

Using an internal timer might not be a best solution for a precise counter, because the error can be up to few percentage. So the clocks will lose its accuracy very soon. To avoid this error you have to use an external timer (e.g. Crystal Oscillator - more to come later on).

Update

So I decided to use an external timer DS1307 RTC (real time clock) module. I've found a RTC library, removed buttons and added the timer.



the numbers have better visibility in the dark than in light room





Comments

Post a Comment

Popular posts from this blog

Counting dice and train wagons using computer vision

Image
Computer vision exercises with preprocessing Before the next project I decided to do some computer vision exercises. Each example is based on a simple logic image preprocessing. No data structure or learning is required. Dice I got this idea while browsing the net. I was curious about how hard can it be to write such a script. I'll describe the algorithm in steps. movement detection : Comparing few frames with thresholds gives us the information, whether something is moving in the frame. Adding some small time frame after the movement stops gives us more precise information. remove background : Thresholding gray frame removes the background and gives us binary image with objects cropping the objects : Using contours to detect object and then separate them by cropping. detecting dots : Inverting the image we get objects that can be again simply detected using contours. filtering dots : If dice is visible also from the side therefore dots from that side can be recogn
Read more

Play table

Image
Using proximity sensors for playing midi tones combined with LED visualization Description The aim of this project was to create a table sized device with multiple proximity sensors that can play midi tones. Each sensor had a few LEDs to show hand distance above the table. This table could be used by one or more persons at once. Hardware setup First I created a prototype from a cardboard to test sensors and some logic behind. Than I ordered a customized plottered sticker with a design which was painted with bare conductive paint. Afterwards I drilled some holes and connected the touchboard with 7 arduino Nanos. Each arduino was connected to 13 LEDs diodes. At the end I added two potentiometers. One for controlling volume and one for changing notes setup. Programming Programming consists of two parts. Master(touchboard) program that reads values from proximity sensors and sends messages to slaves(arduinos). Second program for slaves that reads messages from m
Read more

Skate tricks recognition using gyroscope

Image
In this article we're going to describe how to recognize a skateboard trick using a gyroscope. This sensor is already present in most of the smartphones but in case you are not familiar with it, here is a description . Before we begin, small disclaimer. This project was originally as a part of hackathon that was used with Slido and the purpose was to confirm that it's possible to recognize a trick using a gyroscope. For the sake of simplicity of this project we're not considering skater's stance on a board and we're only trying to recognize 2 simple tricks. So, let's begin by splitting the problem into several smaller ones. We need to record the trick, store it, describe it, understand it, and then of course recognize it. Recording the trick Let's start with the trick recording. To have a precise data we need to have a device with a gyroscope that is attached directly to a skateboard. We need to place it on the bottom of the board, otherwise it might interfe
Read more