"Green" Gator Dot Clock
10 X X 2
X X X
X X X X
9 X X X X X X X 3
X X X X
X X X x AM/PM
8 X X 4
Christmas time is approaching and also one member of our design team is turning 70, so we had to come up with a unique Arduino
(compatible) high tech, cool gift. We only had one day to construct this project.
We decided to "re-invent the clock" and came up with a retro desktop LED clock made from red, yellow and green very low power
LED's. The timebase we chose was the DS-3231 RTC, (ChronoDot from Macetech) which is good for +- 1 minute per year.
By having a Dot Clock with an accurate timebase and built-in DST, just set it, forget it and don't touch it
for 10 years! (Except for 8 years to change the Lithium battery and a minor time adjustment due to +- 1 min. per year error)
We made this clock clean. It has no ugly switches, buttons and manual adjustments. Everything is done by software.
The key to this design is to use an Arduino (compatible) microcontroller to control and compute the proper LED flash
patterns/sequences for displaying time.
We employed the Arduino compatible Rugged Circuits "Gator/Gator+" to drive the special Dot Clock display board.
The Gator's 28 I/O is more than ample for this project. The Gator/Gator+ has current limited I/O, ESD protected IO and over
voltage protected I/O. Using the Gator's "exposed electronics" made it perfect for the "high tech look" for this project
along with the USB power sourcing and the secure spring loaded phoenix terminal blocks.
The operation is simple.
The "Dot Clock" unit of displayed time is every five minutes as opposed to every minute and second on a standard wall clock.
You will never be late with this "Dot Clock" because the time is rounded UP to the nearest 5 minutes.
The "short hand" hours segment always flashes. (yellow "short hand" hour segment with 2 series LED)
The "long hand" minute (5 minute) always stays on steady. (yellow "long hand" minute segment with 2 series LED)
The clock display diameter indicates the hours and elapse minute increments rounded UP to the nearest 5 minutes.
Red LEDs are placed at 12,3,6,& 9 o'clock plus a red LED the center. Green LED's are placed at 1,2,4,5,7,8,10,& 11,
which makes the dot clock easy to read from distances far away. Also, there is a AM/PM red status LED near 3 to 4 o'clock.
Dot Clock Display time examples and operation:
#1. If both the minutes and hours are the same - at 3 and 15 minutes after the hour. Segment 3 will be
flashing at a much higher rate of speed than normal slow flash of the hour hand.
#2. If the "long" minute segment is on steady at 50 minutes and the "short hand" hour segment is "slow" flashing at
segment 2, then the time is 10 minutes till 2 NOT 2:50 OR NOT 50 minutes after 2 or NOT 10 minutes till 3 o'clock!
Since, on a standard wall clock, you can see the hour's hand move progressively towards the next hour, you cannot see
this impending time change on the "Dot Clock". We created a mid-hour correction factor. At halve past the hour, the
hour hand or segment jumps/increases by one hour and all dot clock readings are read "Till the hour". (after mid-hour)
Stated another way, the time reads 5, 10, 15, 20, 25, 30 "AFTER" the hour and then jumps 1 hour ahead at mid hour and
then the "Dot Clock" display readings are all 25,20,15,10,5 "TILL" the hour. Worst case, you could read it wrong and
be 1 hour early but you will never be late!
#3. The AM/PM turns on exactly when it is "PM" and off when "AM".
#4. On the back of the Gator there is the built-in pin 13 red LED which flashes every 500 ms.
#5. The AM/PM status indicator toggles every 1 minute. (For calibration checking)
The 5 minute rounding calculation goes as follows: If the minutes are between 1-4 minutes the time is rounded up to the
next 5 minute "even" increment.
Daylight savings time "spring forward" and "fall back" times are adjusted automatically through "C" code
pre-programmed in the software. (We only decided to program ten years of DST due to the US government's constant
updates and changes - the last government update was 2007)
The Dot Clock 5 VDC power is derived from any USB port @ 100 ma or a wall AC/USB wall cube. (~70ma current draw)
A built-in terminal monitor program, was created for diagnostics and reading & setting times/dates. Rugged Circuit's
FREE GUI terminal program or MS PC Hyper-Terminal can be used with the built-in monitor program.(38,400 8,N,1)
Note: Warning ... use of the Arduino serial monitor built-in to the IDE, does NOT have a carriage return appended to each chr/string entered. (As of rev. 17 ... but this might change soon!)
Note: Even if the dot clock display ceases to function, the dot clock exact internal time base can still be viewed using a
terminal program along with the built-in monitor routines.
Since the Rugged Circuits Gator 324P has another (second) hardware serial port "built-in", we also decided to use the Dot Clock
as a precision internal timebase for our the network timebase on our LIN Bus in our home automation, security and
on our contract development systems.