Table of contents
Abstract
A cheerful Christmas decoration to count down the sleeps until Christmas for the children in the family.
Project
6064.hardware.zip0601.images.zip
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Concept:
A cheerful Christmas decoration which stands in our kitchen and does a countdown of the days left until Christmas for our three grandchildren to see whenever they come to visit (most days 
). Eventually implemented as a happy snowman using an Arduino Nano board as its controller. It has some buttons to press to entertain young minds and fingers.
Storyline:
Built as a Veroboard circuit with my eldest daughter taking care of the snowman model design plus its painting and her husband doing the cutting out of the wood. A real family affair … The original electronic circuit was for four red common anode 7 segment displays which allowed scrolled messages to be displayed. I built this on breadboard with 0.7” single digit displays. It worked OK.
However, I then found some giant– and very bright - 46mm (1.8”) white 7 segment displays by Forge. These were common cathode displays, so I changed the code to accommodate either option. A resistor divider selects the hardware type in use via the Arduino ADC. The white displays actually have 3 LEDs in series for each segment so a higher input supply of 9 to 12V is required. The red CA type can run off the Arduino board 5V which is supplied via a USB cable and standard charger plug.
I found that there was a practical problem with vero stripboard construction in that it is only wide enough to mount two of the white 7 segment displays in the correct orientation. I therefore amended the code to support a 2 digit or 4 digit option. The 2 digit selection only permits the display of numeric values in the range 0-99 whilst the 4 digit option allows for 0-365 as well as alphanumeric text.
The countdown is set by the user when the unit is turned on each day by fixing the day of the month plus the month. This is done by using presses of the UP/DOWN/OK buttons and takes a few seconds to do. I have incorporated an auto-repeat, auto speed-up feature in the code to avoid having to press the buttons many times.
Outcome:
The grandkids really love it and know exactly when Santa is coming to visit! Every visitor to the house has admired it and asked where we got it from and can they get one. Ready for Christmas next year, I will build another couple of Veroboard circuits for the households of my two daughters. These will also have an Arduino Nano host but will use a four digit 7 segment module (for ease of construction) and include a battery backed RTC to recover the time and date the instant it is switched on so there is no need for any user set-up. It will as flash more LEDs as well. I would like to replace the mechanical push buttons with touch switches but that means I will have to ditch the Arduino Nano and go solo with a bare metal Atmel Atmega328PB design. Maybe, maybe …
References
Various 7 segment display data sheets
Arduino Nano user manual
Arduino IDE
