So... you went to the flea market, goodwill
or surfed on line and there was the perfect
peice of junk that you could make the coolest
THING out of. Well I saw this base acrylic
and said wow...what a great egg-timer.
I'll just glue on a few leds, write a quick
code and make a fancy box...easy!
So here it is two months later. My first code
was never going to work. The display was too
big. The case was never going to fit. And
the corner bottom switches could not hold
the weight without staying on.
Step 1: The Layout
I make a grid using fritzing. Then put clear packing tape, sticky side up, over the grid.
This must be taped on all 4 sides. Then place the leds lens up on the grid.
Then add one small drop of SLOW cure epoxy to the tops of the leds.
I make a guide for the glass so when placing the glass over the leds
the glass wont shift and stay centered. I wait overnight and remove the glass
from the tape and check the leds.
Step 2: Acrylic or Pc DISPLAY
You can use a pc board for the leds but nothing beats the beauty of leds on glass.
I spray the back of the acrylic block black...2 coats. Then start to wire the columns
and rows. (12,7) I use coated wire 41-34 size. I have a 'poor mans solder pot'
that makes dipping the ends so they are tined and ready to solder.
If you use pc instead of gluing directly to the acrylic here are some tips.
When done soldering leds to the pc, test display. Then spray paint 2-3 thin
coats of black (not flat) paint. when dry I use lacquer thinner on a T shirt
and flat board to WHIPE the paint from the TOPS of the leds.
Step 3: The ' BOX'
Now the case. I use plain door trim ripped down and mitered
to form the square. I tried those common tact switches at the
corners but the weight of the unit was too much and the
switches would stay on. So I made a front switch section.
I used those alarm beepers with the 'remove after washing'
Step 4: Switches and Pro-mini
The switches are straight forward. All tied to A2.
I don't have much on the circuit because this id the same as my
readerboards. So just a brief description...
I use 595 3 ea. 2 for the column(12) and one for the rows(7).
pins of arduino are 13 to column data
12 to column clock, 11 to both row + col latch
10 to row data 9 to row clock
A2 to switch common 2 to A2 via resistor (this is the wakeup interrupt)
6 is the beeper Don't forget ground + Bplus to the 595
Any resistors will do as long as they match and are over 10k
I happen to have 18k that work very well and because they divide b+
to ground the higher the better. 95k v
B+ o-------ww-------ww--------ww-------ww------o ground D2 o-----ww-----o B+
18k^ ! ! ! ! 4 sw w <18k
Step 5: MORE DETAIL
I included this sch. My scanning in my sketch has the leds
in order. column 1 is always left in a top view. But when you
wire it up you will be upside down. So remember this.
My sketch is basic and easy to follow. I could have
shortened some steps but I left the code easy to follow.
The delay at the end was an after thought but it reduces the
ma draw by 6-7 or about 35% decrease in ma draw.
The delay causes the 'interval' to change and I did not
spent much time in making the count-down to the second.
So feel free to play with these numbers... you might get
this accurate to the second.
Step 6: Final Notes
The unit uses a mini pro and runs well on 3 aa batteries. I have run several units
their full count of 90+ minutes and beeper alarm for more then 22 cycles before the
display starts to dim. That's more than 30 hours or 600 three minute eggs!
The acrylic blocks come from 'collecting warehouse'
www.CollectingWarehouse.com in OHIO ....not china!
Many timers count down and when
they reach the end and they just cut off or sound
a breif alarm. You come back and never know how
long ago the timer stoped. This timer counts
negetive for 5 minutes. You could make this longer
but remember it runs on batteries.
The real problem comes from showing my projects
to my wife. I would bring a beradboard full of
wires to the kitchen table. Proud of the secret
display only to hear 'get that off MY table.'
So I would dress it up but ...trust me...
tupperware containers still dosen't work.
Then after 7 board feet of wood, glue, epoxy,
paint, sanding... I'd take the project upstairs.
'Well that looks sorta ok. Put IT on YOUR table'.
Now for the best part. You move on to three more
projects. Then you hear 'DEAR... my friend saw
that THING on your table....could you make her
Words of advise. Always keep detailed notes. No
matter how stupid or simple the project is. At
some time later you will return to that project
if only to try and remember how you made a circuit
or a line of code. Which leades us to the age-old
question... Why do husbands die before their wives?
Because they want to.
good luck. I hope I inspired you to be more ingenious
and spend hours in the garage...further away from
you know who.