hi
i have an arduino nano 3.0, attached to which are Bluetooth module(3v3) and ultrasonic sensor (5v) both were working fine till today but today they stopped working so i checked the stats i found that 3v3 was dropped to 2.7v while 5v to 4.1 v. i haven't checked for other digital or analog pins for error. also i tried using it with nothing attached still were dropped.
i am powering it through Li-ion 9v 1ah external battery. Also powering through usb gives 5v----4.7
3v3 ---- 2.9 ......
- no drops in battery battery is giving perfect 9v
pleaseeeeeee helppppppppppppp!!!!!!!!!!!!!!! 
What voltage are you getting out of your "9V" battery?
The 5V is derived from the voltage regulator on the board. Depending on what one is used it could have a 1V dropout voltage which means if your battery voltage drops below 6V (when connected) then the 5V to the arduino will be below what it should be.
The 5V line should not drop below 4.5V.
If the battery is putting out a solid 9 Volts under load, and the battery is the only thing connected to the Arduino Nano (via GND (-) and VIN (+) pins) you should be getting a solid 5V out of the Arduino Nano 5V regulator unless the board is faulty. Ask your vendor if you can get a replacement board.
Thanks a lot for the feedback.....
But unfortunately my vendor doesn't provide replacement...
Can there be any other possible reason that it might be not working. As it was working till yesterday, it might be my fault.
Any tips so it might not happen again...
One other thing I remember is that while fabrication of the circuit the person by mistake connected a capacitor between 5v and GND however I removed as soon as I figured it out. Can it be a reason........
Again thanks a lot for the feedback...
Typically damage will occur when the power gets shorted to ground. It can also happen when one or more output pins are grossly overloaded. It may be possible to replace the 5V regulator but that will take some soldering skill. The easiest solution is to get a new one via eBay for under $2.
My nano uses a AMS1117-5.0 in a SOT-223 package mounted underneath at the opposite end to the USB connector. You could replace it as you would probably get 50 of them for about the price of a nano but it is not particularly easy if you don't have a hot air rework station and you might end up damaging the board. For $2 the simplest and cheap solution is to get a new nano and that will also tell you if the other one is faulty.
The AMS1117 is rated for 800mA but the tab is not connected to much metal so it would overheat well before that.
2 further things I noticed were
That the person from whom I fabricated my circuit he by mistake installed a capacitor between 5v and GND .
Secondly I noticed that 3v3 and all the digital pins were also dropped.
Is it just because of the 5v regulator.
Please reply
And thanks a lot for the suggestions I ordered a new nano. From Amazon.
naman0987:
That the person from whom I fabricated my circuit he by mistake installed a capacitor between 5v and GND.
A capacitor across 5V and GND could briefly cause a high load on the regulator when power is applied but would otherwise be harmless. It might be possible that the capacitor damaged the regulator.
naman0987:
Secondly I noticed that 3v3 and all the digital pins were also dropped.
The digital outputs will always be the same as the voltage input. The 3.3V regulator in the FTDI chip SHOULD be able to provide regulated 3.3V from a 4.1V input. It's beginning to sound like the place where you attach the negative probe of your meter is a diode drop above Ground.
How do you connect your meter?
naman0987:
Is it just because of the 5v regulator.
If the input to the regulator is 9V and the output of the regulator is 4.1V then the regulator is not doing the job it was designed to do. Either the regulator is damaged or the rest of the circuit is bad.
The 3.3V is generated by the FT232 chip that gets its power from the 5V. So a faulty 5V can very well result in a faulty 3.3V
I connect the multimeter on DC voltage mode.
- point of multimeter with 5v / 3v3 / any pin
And
- point of multimeter with Gnd
*** correction I had a clone with ch340 instead of ftdi chip.