Bypassing the Vreg and supplying your own 5V, you can get down to 5v
4x Nimh Batts are ~4.8V...... close enough? How about 1X Li-Ion cell at 3.7V?
I am trying to design a simple shield that will be battery powered and would love to not have to build in a boost converter if I can get away with it. I've been reading the datasheet and the charts aren't exactly high precision... LOL.
It lists 2.7v as "safe" to 10 Mhz, and 4.5v as safe to 20 Mhz...... 10 Mhz over 1.8v... 0r .18v/Mhz. 10 Mhz @ 2.7v plus .18v x 6 Mhz... 3.78v as a bottom end safe voltage @16 Mhz? (It's probably not exactly linear.... but it's something to guess on...)
My take.... 4.8v is just fine..... 3.7v is really pushing it. Dang it, so close yet so far... LOL.
Does anyone have real world experience? I'm hoping that the "Safe operating voltage" means it may cough and screw up once in a blue moon but will basically be just fine.
Keep in mind that is a nominal cell voltage, the actual voltage ramps down from 4.2 at full charge down to 3.0 where most people stop or risk damage from over discharge.
Why fool around, just use a very small and inexpensive switching regulator module:
I'm designing a board intended to be a lightsaber "shield" for the Arduino nano, (.7" x 2.25" Hopefully) which will house a microSD card, accelerometer, audio amp and 1.X amp PWM controllable LED driver.
People regularly choose 1x L-ion, 2x Li-ion or 4x NimH batteries. (They most readily fit inside a lightsaber "hilt".)
I would (and will) include a switching regulator if space allows but the board is small.
It may be better/easier to indicate they need a step down for 2x Li-Ion, a step up for 1X and are probably OK with 4x NimH. As you point out they are easy/cheap on Ebay and you can customize it to fit the need.
Anyway, the idea is using off-the shelf components and with freely available files (Eagle, gerbers, code, etc) so anyone can build thier own or modify it, etc. While there are commercial options out there none are fully programmable like the Arduino which I think will appeal to some designers. In my case, I want a full color lightsaber and nothing else controlls RGB, LOL. (The WIIFM...
In terms of battery for your light saber, I was looking for accessories for my new Samsung Galaxy S-II cell phone, and I noticed this battery on ebay: http://www.ebay.com/itm/330772818549?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649. Unlike most of the batteries I've seen, it is only 22mm (0.87") in width, which might work well in a light saber handle. The power is 1850 maH. For a comparison, I ran my normal Arduino Uno with a 5000 maH battery doing blink, so it should give you about a day at a convention before you have to recharge.
