The presence of 12-Multi-National Digital clocks is very common at the lobby / front desk of star hotels, showing time & dates of several countries where from most of the guests to arrive to stay at the hotel. One common feature of these clocks is that they are majestically looking elegant dial clocks!
I tried to achieve that feature using a cheap ATMega-328 alias bare-minimum Arduino UNO microcontroller [which hardly costs $3 per piece], few cheap 128*128 TFT displays and an RTU DS3231.
The principle of operation:
The DS3231 is a very precise RTU which has an inbuilt temperature sensor for adjusting the clock frequencies for temperature corrections. It maintains very precise timings over long durations. DS3231 connects on I2C Bus.
Each TFT ILI9163 is a 128*128 dots color display runs on SPI bus along with Reset & AO pin and it needs only one extra GPIO pin per display to complete its connection with the Arduino. That is the crux of this cheap yet versatile multi-nation digital clock and the cost is $46 for 12-display system.
Let us see how?
Each TFT ILI9163 Runs on 5volt / 3.3volt and has the following pins – VCC, GND, LED, CS, RST, AO, SDK & SCK. Out of these VCC, GND, LED is common pins. The remaining pins can be common depending on the choice.
|ILI9163 Pins||Nature of pins||UNO pins|
|VCC||5 volt / 3.3 volt||5V / 3.3V|
|LED||5 Volt / 3.3 Volt||5V / 3.3V|
|CS||Must be different pins for each display||A1||A2||A3||Digital pin 2|
|Reset||Can be common or RES pin of UNO||RES pin of UNO|
|AO||Can be common or Different pins.||A0|
|SDA||Fixed pin for all displays||Digital pin 11|
|SCK||Fixed pin for all displays||Digital pin 13|
|DS3231 Pins||UNO Pins|
Using the above tables one can see that apart from 5 fixed / specific pins, for each UNO pin one can create one country-specific display. Like – A1, A2, A3, D2, D3, D4, D5, D6, D7, D8, D9, D10
Total 12 different national clock display can be created on one UNO!
* D0, D1 & D12 cannot be used as they are special purpose pins.
Schematic: [for 4 displays multi nation clock]
To add more displays, just repeat the connections.
Bill of Materials & Price for 4 displays a multi-nation clock
1 * DS3231 – $1
1 * ATMEGA328 / UNO – $3
4 * 128*128 TFT [ILI9163] – $14 [$3.5 a piece ]
For 4 display multi-nation clock = $18; For 12 display multi-nation clock = $46
The schematic is shown for 4 displays a multi-nation clock. To go up to 12 displays, to just add so many displays, repeat the connections and make necessary changes in the sketch.
Here I have just built up a 2-display-clock. To add more displays, Just follow the sketch, repeat the display connections & make necessary changes in the program sketch and you will be able to build your 12-nation-clock in no time.