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How safe/dangerous is it to operate an Arduino Nano 5V with a varying voltage source?
I have a circuit that provides a duration of power with a starting voltage of 5.3V and an ending voltage of 4.5V. I'd try it myself but the time and money of ordering another chip is rather disincentivizing.

Will a higher or lower than rated voltage affect the processor speed? How will a varying voltage affect the I/O pins I've read on forums that people say that sections of the chip will 'brown out' if not given enough voltage what does that mean?
Please help.

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migrated from arduino.stackexchange.com Mar 17 at 21:08

This question came from our site for developers of open-source hardware and software that is compatible with Arduino.

2 Answers 2

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Maximum voltage for the ATMega328 is 5.5v, so you are safe there.

Minimal voltage is 1.8v, though lower voltages don't damage the chip, but could lead to unexpected behavior. By default Brownout detection is enabled, so the Arduino will just reset itself, if the voltage is below 2.7v.

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the unexpected behaviour comes from the fact that if you are running at a high clock rate (16Mhz+) anything less than 4.5V may not operate properly or you may have random errors creep in from failed/missed clocks –  KyranF Mar 17 at 21:23
    
@KyranF thanks for pointing that out. I forgot about that. However that 4.5v figure is for the maximum 20mHz frequency. For 16mHz its around 3.78 volt (looking at Safe Operating Area graph). –  Gerben Mar 18 at 11:06
    
@Gerben If you've looked at the actual graph then a link would be useful (assuming it was online). –  Russell McMahon Mar 18 at 11:55
    
Here you go; Datasheet page 303 (chapter 29.3) –  Gerben Mar 18 at 14:01
    
Of course, but a varying supply is something the original question needs to take into account, so that the lowest expected voltage is still going to work for that (fixed) clock frequency –  KyranF Mar 18 at 20:24
up vote 1 down vote

It is likely that the range of voltages that you have specified are acceptable.
However ...

The processor datasheet publishes acceptable clock speed and voltage "mappings".
Operating outside the specified ranges may lead to indeterminate operation. If indeterminate operation is acceptable to you then operation outside specification may work for you. If you are making products for customers or employers they may not be as accepting as you are.

"Brownout" is a condition which may occur when a processor is run at a voltage below specification. In "Brownout" anything conceivable may happen and a few inconceivable things may happen as well. In some cases the system cannot be reset with the external reset line and full poweroff is needed to restore sanity. To avoid this happening many microcontrollers incorporate an "anti-brownout" system which rests the processor if supply voltage enters the danger region. For a processor with a wide range of allowable operating voltages or several clock versus voltage zones, the anti-brownout trigger level can usually be user programmed to suit requirements. A brownout state MAY be triggered by a very short below-spec pulse on a power supply line. Anti-brownout detectors must be able to detect and react to any voltage dip which may cause processor mis-operation. In some cases, adding an anti-brownout function may increase the number of system rests occurring as pulses are acted on which do not in fact cause processor pro;lems. This is more acceptable than failing to detect dips which may cause problems.

ANY serious microcontroller system that is intended to provide reliable operation must use a properly configured anti-brownout system. Microcontrollers which do not have such a system should be avoided.

The diagram below shows how to interpret the datasheet power/clock-speed mapping for one AVR processor. Whether the bounds shown are relevant to your processor can be determined from the data sheet. Familiarity with "Dirty Harry" nomenclature will ease interpretation of the labels.

enter image description here

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inconceivable! haha. And nice Dirty Harry chart too. –  KyranF Mar 17 at 21:24
    
Rather odd. Most operating rooms don't have that shape. Must be unsafe to have an operation in those hospitals. –  Gerben Mar 18 at 20:29

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