Hello,
I have a 2.3V super capacitor that i need to use for a school project, can i power the arduino uno with this voltage?...
No.
fungus:
No.
out of curiousity, what is the minimum voltage that i can use with the board.
The USB chip requires 5V.
ozwurld:
fungus:
No.out of curiousity, what is the minimum voltage that i can use with the board.
The Mega328 chip which is the "brain" of the Uno will work at lower voltages but the Arduino Uno board is designed for 5V.
Plus...supercapacitors often have very low current output (amps). It might not be able to power a Mega328 chip even if you find a board which works at 2.3V.
You can probably power the ATMega328. It will go down to 1.8V at lower speeds. I've actually done this before using a Renesas chip, but I don't remember exactly the voltage rating of the supercap we used, or even which chip it was. This was for a class project where we were graded on power reduction based on how long we could run a particular script off the super-cap. So it should be theoretically possible on the ATmega. However, as for the other parts, like the USB, etc, no, those need 5V.
Couple of things,
Most supercaps have very low current draw allowances... on the order of 1-5mA. You can certainly keep an RTC alive on this power supply or preserve the contents of the Arduino RAM while changing batteries, etc. but it's not meant to power a MCU unless you buy a supercap that allows much higher current draws (they tend to be 1F and up) and combine that with a boost switchmode regulator to pull all the available power out of the supercap. Multi-Farad supercaps (and you'd want a dual-layer model, if memory serves) are not cheap and a boost converter is just what the doctor ordered to realize their full value.
Even so, I would expect you would have to put the MCU to sleep most of the time to conserve power. A LiPo battery pack may be a better and cheaper solution.
The fundemental problem of trying to use 'super caps' to power ucontroller ships is that a cap's terminal voltage drops in a linear manner determined by the R/C time constant where the micro's current draw represents the R. This unlike batteries that maintain a nominal constant terminal voltage through out it's capacity rating (either expressed in AH or mAH). Micros usually require a regulated constant voltage, even if they have a wide range of voltage they can work with, but a constantly decreasing Vcc that varies with current draw would make for a pretty fragile environment in my opinion. I could only see a 'super cap' possible being useful as a 'stay alive' circuit if one put the micro in some kind of deep sleep condition and needed to remove the normal Vcc voltage source. If the super cap was diode isolated from the main voltage source it could continue to keep the micro in sleep mode thus saying state of SRAM and control registers for some period of time until the normal Vcc could be replaced?
So my bottom line opinion for the OP's question is NO, except for possibly some exotic short term 'back-up' mode.
Supercaps have enough leakage to make them only useful as backup
during short periods, and are used sometimes to permit battery replacement
without losing state (The RTC in a digital camera for example could be
done this way).
Specialised high-efficiency supercaps are available for power use, but
will probably always be uneconomic compared to a battery for powering a
microcontroller - batteries store orders of magnitude more charge and
have almost constant voltage.
If your supercap has a low ESR, it can be charged up from 5V, and then when 5V goes away the cap output can be used with a boost regulator to allow storing critical data to EEPROM for example for faster recovery on startup.
It needs to be low ESR tho.
Thanks for the reply everyone. I have to use a supercap for a class projct.., so im going to use a boost converter and have its output regulated at 5v. i will see how long this lasts.
Thanks again/ 
Most supercaps have very low current draw allowances
This is no longer true. These days, supercaps are being used to IMPROVE the pulse current characteristics of batteries that are already relatively powerful. Of course, the supercaps intended primarily for things like memory backup power still exist as well, so you do need to try to find specs for your particular supercap. If it's one of those freaking huge "BoostCaps" that have been appearing on the surplus market, a boost regulator might be reasonable.
One of the super-cap vendors (cooper bussmann) has a "capacity calculator" spreadsheet that you can download and plug in values like "charge voltage" (2.3V), minimum useful voltage (1.8V?), time required, and etc, and it will give you the unknowns: http://www.cooperindustries.com/content/public/en/bussmann/electronics/resources/library/apps_notes_technicalinfo.html
it can be charged up from 5V,
Um. Not recommended if it's a 2.3V supercap!!
The Uno is not a low-power board, and has several components that require 5V. The ATmega328p processor itself has a maximum frequency specification that depends on the power supply voltage. The Uno has a 16MHz crystal, and the lowest operating voltage that will support 16MHz is about 4V. It can operate down to 1.8V at 4MHz, but running at that speed would require board and arduino core modifications.
mirith:
You can probably power the ATMega328. It will go down to 1.8V at lower speeds.
You'll need to reprogram the boot-loader to go this low as the standard bootloader
for has the brown-out voltage set at 2.7V
MarkT:
mirith:
You can probably power the ATMega328. It will go down to 1.8V at lower speeds.You'll need to reprogram the boot-loader to go this low as the standard bootloader
for has the brown-out voltage set at 2.7V
Just a simple edit of the boards.txt board entry fuse value and then reburn the bootloader, no?