I requested this sample from Molex:



IMAG0766 by jg1996business, on Flickr


IMAG0767 by jg1996business, on Flickr

the datasheet is here:

http://www.molex.com/pdm_docs/sd/5035000991_sd.pdf

My question is, how do you solder those little tabs to your board?

Excellent!  and thank you!  So my steps will be:

1.  Upload the ArduinoISP sketch onto an Arduino Uno following these instructions http://arduino.cc/en/Tutorial/ArduinoISP
2.  Connect the Arduino Uno to my new mega328 as shown in the bottom images of the above link
3.  In the arduino dev environment go to tools-->programmer and set it to "Arduino as ISP"
4.  In the arduino dev environment go to tools-->board and set it to "Arduino Pro or Pro Mini (3.3V, 8 MHZ) w Atmega 328
5.  In the arduino dev environment go to tools-->Burn Bootloader

So now I should have a mega 328 that I can run off of 3.3V reliably but that I could still program with 5 volts via the arduino uno with its mega328 removed.  Is this correct?  Will the Atmega16U2 on the Uno have any problem communicating and uploading sketches to a mega328 running an 8MHZ boot loader?

You could also just put it on the breadboard and connect the ground, reset, rx and tx to the arduino board that way you dont have to keep putting the chip in and out of the breadbard and arduino.

Also if you are doing anything time related you are still going to want to use a crystal and you'll need a bootloader meant for external 8mhz. If no time, then nevermind.

Is it safe to assume that anything involving the UART would be considered "time related"?  I was planning on using an 8MHZ external crystal for timing.  Is it a completely different bootloader that is needed or can I just modify the setting of the fuse bits in the boards.txt file in the hardware folder?  Couldn't I just compile the program as if I am using an arduino pro running at 3.3V and 8 MHZ and then program it through an old arduino board that still uses the FTDI chip (if using the FTDI chip versus the Atmega16U2 on the Uno even matters)?  I really don't understand how all of these parts on the arduino talk to each other. 

Thanks.....I will give it a try!

Well sure I could buy an off the shelf product like a gps watch but that isn't any fun

I want to run a mega328 at 3.3volts so I was looking at this tutorial
http://arduino.cc/en/Tutorial/ArduinoToBreadboard
and this tutorial
http://arduino.cc/en/Tutorial/ArduinoISP
to make it happen.  If I can get the bootloader onto the breadboarded mega328, will I be able to use an arduino uno (with the uC removed) to program the breadboarded mega328?

Is there a way to predict how long a battery with a certain capacity will last if I know the current draw of each device that it will be powering?

A one amp hour battery capacity (1000mAH) will power a one amp load for one hour, a 100ma load for 10 hours, a 10ma current load for 100 hours. I think you see a math thing at work in there somewhere?  

Lefty

Yes but isn't the voltage slowly falling over that 1 hour period (in the case of a 1000 mAH battery powering a 1 amp load)?  Wouldn't the voltage fall to a level that is un-useable before the hour is up?  Or does the battery capacity suggest an amount of power that can be delivered before the voltage starts to sag?

I didn't realize that coin cells were so limited.  I'm glad I asked this now.  I originally had suggested that my wife use a running tracker app that she can get for her android phone but she doesn't want to have to carry the phone on a run because it is too big.  What I plan to make for her will be a lightweight box that is slightly bigger than an arduino nano that she can wear on a lanyard around her neck.  I think a battery such as the ones that come in those tiny remote controlled helicopters may be appropriate.  Is there a way to predict how long a battery with a certain capacity will last if I know the current draw of each device that it will be powering?

My wife wants a gps tracker to wear while jogging, and given my propensity for DIY, I decided to make her one.  I am going to use one of these:
http://www.mouser.com/Search/ProductDetail.aspx?R=A2035-Hvirtualkey99990000virtualkey927-A2035-H410
for the GPS module and I am going to use an arduino (well really just the mega328 programmed from the arduino dev environment) and an sd card to log the data in comma delimited format.  I want to run it off of coin cells and have them last as long as possible so I will be pretty liberal with sleep mode on both the arduino and the gps module.  The gps module needs 3.3 volts so I was thinking a switching regulator would be appropriate to get maximum life out of the batteries.  I was figuring running the whole project off of two 2032 coin cells.  Does this switching regulator seem appropriate to supply 3.3v from the two 2032's?

http://www.ti.com/lit/ds/slvs417e/slvs417e.pdf

Thanks guys!

I was thinking of using a 74HC4050 hex buffer (I guess that is what it is called) for interfacing an arduino to a number of 3.3v peripherals.  I was using Mousers compare feature to compare the two available IC's on this search:

http://www.mouser.com/Semiconductors/Logic-ICs/_/N-4s5z6?P=1z0z44d&Keyword=74hc4050&FS=True

As far as I can tell they are virtually identical except it seems that the TI chip has lower propagation delays (which I would guess would be a good thing).  STMicro's chips are $1.50 a piece and TI's are $0.45 a piece.  What am I missing?

Thanks guys!

I guess the subject says it all.  According to the datasheet, the mega328 can run off of voltages from 1.8 - 5.5V.  I know that Vin goes to the voltage regulator but the 5V pin I believe goes straight to the mega328 so can I just put 3.3v on that pin and run the whole nano at 3.3v?

Excellent!  Thank you very much!  Order placed with mouser.

It just starts spitting out NMEA data and they work good I use them for time stamping timing critical events on remote nets.  If you contact tech support with Maestro you email with "Larry" and this is not much better than the manual but once he understands what you want and stops telling you really basic things off his troubleshooting sheet you get what you need from someone behind the curtain.  Given the $20 cost for a fully functional GOS with PPS it is a great deal, even with the poor docs. 

They are surface mount parts but hand solder very easily.

Regarding the shutdown shutdown stuff I just wait the second  then shutdown power.

Thank you so much for responding to my question!  So when you say that you just shutdown power after a second, is this after you do the 200ms high/low pulse on the ON_OFF pin or do you just wait for the wakeup pin to go low and then count 1 second after that?