"Green" Gator Dot Clock

Forum 2005-2010 (read only) General Exhibition
7

Amazing, too, that it was a one-day design.

It took many hours on the deck drinking "liquid refreshments" to come up with a general design spec. (See below)

It took three team members to design it. Printed circuit board design, enclosure/mechanical and software sketch.
The design of the printed circut board took 1/2 day and we waited 5 days to receive it from ExpressPCB.
In the mean time, it took only 3 days for parts from Digikey and only one day to construct/assemble this project.
Software debugging is an ongoing process - so far there are no major bugs.

"Green" Gator Dot Clock General Design Specs:

  1. 1 day for board construction, enclosure assembly and software testing.
  2. Green - very low power operation. (All T1 3 mm LEDs have a 2 ma current draw each)
  3. Reliable and accurate - see timebase options below.
  4. We decided to employ the Arduino compatible Rugged Circuits "Gator" to drive the special dot clock display board.
    The Gator's 28 I/O is more than ample for this project. It 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.
  5. All passive display components - no IC drivers/multiplexors/port expanders.
  6. The clock timebase that was chosen (below) was the DS-3231 - "Chronodot" by Macetech $14 <-- "The Industry's most accurate RTC" by Maxim Semiconductor.

Timebase design options:
A. 60 HZ power line with microcontroller decode <---- not accurate.
B. Caller-ID using modem decoding <---- expensive plus caller-ID service is required.
C. PC clock with serial updating (Python script) <--- not practical for standalone operation.
D. NTP Network / Server with Ethernet time update <----- very expensive and not practical for standalone operation.
E. GPS NEMA decode <---- expensive & un-reliable and won't work in older homes with chicken wire plaster and even new homes with high ambient noise.
F. Software Real Time Clock <--- not accurate & un-reliable due to Arduino time base crystal and having a reset causes the clock to be adjusted again.
G. WWVB C-Max decode <--- expensive and un-reliable and won't work in older homes with chicken wire plaster and even newer homes with high ambient noise.
H. Local hardware I2C timebase with Lithium battery backup ~ 8-10 years.

  1. DS1307 I2C realtime clock with -+ 2 minutes per "month" accuracy <---- Used in first beta prototype ~$5 from Futurlec & $20 from Sparkfun.

  2. DS3231 I2C realtime clock with _+ 1 minute per "year" accuracy <---- Used in final design - drop in replacement (register wise/ address ).

  3. Simple to operate and no pushbuttons. The clock is re-calibrated by uploading the proper time via program sketch or serial terminal monitor routine.
    The daylight savings time and "spring foward and fall back" 1 hour adjustments are done automatically in software. This dot clock time display readings should be
    good for 10 years with no manual user inter-action. (10 years of daylight savings dates were programmed into this clock)
    The US government changed again the DST dates in 2007 and a lot of digital clock manufacturers were stuck with the wrong switchover DST dates in their "fixed clock" design.
    By using this computer controlled programmable clock this would never happen!

  4. Clock display is always fast by design (1-4 mins). Limited I/O and LED board placement which prevented from showing the minutes and hour offset.

  5. Make the dot clock "unique" and as high tech gift which cannot be purchased anywhere.

  6. Wiring from all electronic modules must be organized and neat due to the acrylic enclosure.

  7. Use low cost "dot" display components. (< $8.00) <<<<<<<<<<<<

  8. No surface mount components on the clock dot display printed circuit board.

  9. No prototyping - this design is extremely simple. (In fact, the display board could even be constructed on a perf board or Arduino shield.)

  10. Piggy back mount all modules with standoffs. The dot display, DS1307/DS3231 RTC, the front panel clock faceplace, and the Gator mounting
    are all to be mounted together as on integral unit for the high tech display look in the highly polished acrylic enclosure.

  11. Use a highly polished acrylic enclosure and clock stand. (Acrylic jewelry box and plate stand from The Container Store)
    No user physical contact with the electronics will be allowed even though the Gator has all I/O ESD protected and is almost indestructable.

  12. Make the dot clock design so the dot clock can drive a custom designed "future" 3D laser engraved block of crystal (glass). <--- very expensive but cool.

  13. Design a "optional" clock faceplace for the dot clock. <--- not really needed due to high vendor cost and use of multi-color LEDs.

  14. Cast the dot clock display in plastic resin which includes the front dot display and faceplate for the high tech design look. (In the future)

Note: Casting in plastic resin is an art form in its self. The casting temperature, humidity, curing time, curing catalyst,
resin mixing and pouring procedures are all critical for a proper water clear glass like cool look.
Embedding the electronics in resin won't occur until the electronics are "burned in" and the LED lighting is at a
constant MCD intensity. Having just one LED burn out renders the whole resin casting and dot clock almost useless!
19. No extra power supply and low power green operation for USB < 100 ma. (Power came out to 70ma)

:sunglasses: :sunglasses: :sunglasses: