Hi, just as a quick question..
I am designing some sort of stand alone thingy here.. do you think it is possible to run an Arduino and an additional LCD as well as a few sensors for a reasonable time (min 1h) on 4 AA batteries?
I think i will need some sort of Mintyboost parts as well - can i simply copy the mintyboost structure or am i needed to turn up with something completely new?
The regulator used on the Duemilanove can provide adequate voltage (5 volts) with an input voltage of 6 volts or more on the Vin pin. Four AA Alkaline batteries will deliver at least 6 volts for most of its useful life so that should work. Rechargeable Nickel cells have a lower voltage so you would probably need 5 cells to make a 6 volt pack if you used NiCads or NiMH cells.
There is a reverse polarity protection diode on the DC connector that drops the voltage by 0.7 volts which is why the Vin pin should be used instead of the DC connector for your application. Your battery voltage should be 7 volts or more if you use the DC in jack. You can damage the controller chip if you don't connect the power correctly so take care in connecting the positive and negative battery wires (positive to Vin, negative to Gnd)
I would expect you would get more than an hour, how much depends on the current required by the LCD (most if this will be drawn by the backlight)
There would seem to be two approaches.
The 'mintyboost' voltage converter approach should have less energy loss (using the 5v/usb arduino input) than the Vin/9v or power connector - both of which use the on-board regulator (which actually gets warm with the energy it dissipates).
Which is best in practice?
According to the article on Mintyboost linked below, Mintyboost is around 82% efficient with two AA batteries. Using 4 AA Alkaline batteries through the regulator should give similar efficiency (and twice the duration because of double the number of cells). 4 AA alkalines is the cheaper solution but MintyBoost is better if you want to use recharagable batteries (or just two cells to reduce the size and weight). MintyBoost would also be more tolerant to very weak batteries.
A good Mintyboost technical article.
http://www.ladyada.net/make/mintyboost/process.html
I'm pretty sure if you want to run on a stable 5V, 4x AA batteries will not work unless the voltage regulator is replaced with a low dropout regulator. The 5V regulator on the duemilanove needs 7.5V to run properly if I'm not mistaken.
I'm pretty sure if you want to run on a stable 5V, 4x AA batteries will not work unless the voltage regulator is replaced with a low dropout regulator. The 5V regulator on the duemilanove needs 7.5V to run properly if I'm not mistaken
Scott S, the regulator on the duemilanove has the dropout specified as less than 1 volt. I measured my board and the +5v line was within 5% of 5 volts with 5.75 volts on Vin. The 7.5 volts refers to the DC input jack and it is a conservative value. See Post #1 for more info on why there is a difference between the Vin pin and the DC jack.
The regulators on some earlier boards used 7805 regulators and these do have a higher dropout than the one used on the duemilanove
I had assumed the regulators on the duemilanove were 7805's thats why I claimed this. I've run a duemilanove off 6 AAs before without a whole lot of luck (it ran but ran undervolted, so sensors were inaccurate)
I wonder why 6 cells did not work? Even 6 Nickel AAs would have a nominal voltage 7.2 volts and that should be enough for a Duemilanove. Did you measure the voltage on the pack at the point you started to have trouble? How much current did your application required?