Binary Clock Charlieplex

[Snipeye]

So, I'm making a binary clock (a wristwatch, I was hoping) but I need a little help:

I have this charlieplex library:  http://www.arduino.cc/playground/Code/Charlieplex

Is there a newer version, or will that work just fine?

I plan on using this ATTiny, http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ATTINY25V-10PU-ND - Is there perhaps a different one you would suggest?

Last, not really related to this forum I suppose, but I was wondering about battery life.  I mean, with charlieplexing only one LED at any given time is on, so I shouldn't have too much current draw - but I still have no clue what power source to use.  I want to make this a wristwatch, so a coin cell (perhaps multiple) would be ideal, but I really have no idea.  Any suggestions?

LAST:  I want to use blue LED's, but if battery life makes that impractical, what kind would you suggest, what specs, etc.  If blue LED's would work, once again, what kind/specs should I look for?

[MarkT]

Firstly get ultra-bright LEDs and use a small current (1mA or less should be fine).

Secondly what voltage?  Coin cells have a tiny tiny capacity, a small LiPo cell would be much better (and gives 3.6V or so in one package) - however I'd not be too happy with a LiPo cell strapped to my wrist given the fire risk.

Note blue green and white LEDs take a higher voltage than red/orange.

If you use a RTC (real time clock) chip or module then the display driving circuit can be powered off until its needed, RTC chips like the DS1307 (or DS1338-33 for 3.3V) will run for years off a Li coin cell because they take about 300nA.  A separate battery for the MCU and display is desirable, adding complexity.  If the display is only powered up when pressing a button switch a coin cell might be enough for that too.

Sparkfun do an RTC module incidentally.

For reference I've made a timepiece (little bit big to be a watch really) like this - it uses an RTC chip for keeping time and a ATmega168 to drive small 7-seg LED display.  One AAA NiMH 1000mAh cell and a boost module to 3V3 powers the display for about a day only.  If the 168/display is activated when needed it would last months (till the cell self-discharged).  The RTC runs off a CR1225 coin cell and should last 10 years.

[cmiyc]

LAST:  I want to use blue LED's, but if battery life makes that impractical, what kind would you suggest, what specs, etc.  If blue LED's would work, once again, what kind/specs should I look for?

I don't know what you consider to be impractical.  This past holiday I received the Binary Watch sold at ThinkGeeK as a gift.  It has blue LEDs but I have no idea what the display method is.  They are so bright I wouldn't be surprised if they are directly driven.  (However because of how even the lighting is regardless of the time, I suspect there is some multiplexing.)

With two months of telling time + lots of extra demonstrations the coin cell is holding well.  For me, the battery lasting one month was all I expected.  Like I said, I'm on almost two already.

[Snipeye]

Well, are the LED's SMD in the watch you have?  I think they use lower mAh.  I'm thinking of using 1 AA and boosting it to 3.3v - a bit clunky for a wristwatch, but it'll do.  As to using an RTC module, an interesting idea, but I want to keep this project more simple (I.E., clock off the ATTiny).  Battery life from the AA would depend on the draw of the ATTiny - boosting a 2000mAh 1.5V AA up to 3.3v at roughly 90% efficiency will give me about 900mAh at 3.3v to work with - just driving the LED's, that's a little over a month straight.  I found some Surface-Mount green LED's that use 2.1V @ 1mAh, and I might be able to solder to them... hmm...

I've just been working on the actual charlieplexing part in EAGLE, and the circuit board layout is a pain.

[billhowl]

http://wn.com/Binary_Clock_using_the_Arduino
http://www.youtube.com/watch?v=LVJdWvtOdpc&feature=player_embedded#

[Snipeye]

Alright, I think I've got both Charlieplexing and the other clock code/displaying in binary worked out.  My final concern is battery life - boosting a single AA to 3.3V at 80% efficiency (about the best I can hope for, I think) I'm getting about 1Ah, total.  The LED's will draw around 20mAH, I think, but how much does the ATTiny draw?  That's the last thing I need to know.

[billhowl]

Base on the datasheets if operate 1MHz 1.8V it draw 300 micro Amps. so if you operate at 3.3V map be about 1mA.

Please read the section 7 on power consumption issues. like disable ADC, all port pins was avoid unconnected, have a defined level. Connecting unused pins directly to VCC or GND is not recommended, since this may cause excessive currents if the pin is accidentally configured as an output.

[Snipeye]

Well, I'm using the 2 remaining pins for buttons to set the time, and then a button to display the time - to save battery, the LED's will be off unless I press I button that tells the arduino to display the time.