Arduino Mini PRO 5v at VIN Possible Damage

Hi,

Before posting this question, I have gone through several posts that advocate that anything 5V regulated should go to VCC and I absolutely respect the logic behind that. I have a simple setup whereby I have connected the following through a Step Down Buck convertor that brings down a vehicle's unregulated 12v to 5.1v.

Arduino Mini PRO 5v version
DS3231 RTC
SSD1306 OLED.

The step down is performed by this module. which also powers all other modules including the Arduino.

As the module powers the Arduino through VIN, I observe 4.5v at VCC. There are no modules connected to Arduino on the VCC pin, although I/O functions are performed to and fro other modules with the Arduino.

Another aspect of the setup requires it to remain active for some time even if power is disconnected to the Arduino. There's a 5.5v 4F supercapacitor that is employed to perform that function. Here, as the voltage drops below 3.5v, the Arduino begins to reboot for about 3-4 times until, it can no longer do so as the voltage drops further.

There are few things about which I need guidance regarding this setup. I'm aware its not ideal and the Arduino is being run in an undervolt condition.

  1. Do I run a risk of damaging the Arduino or any other component or module in this setup?
  2. Even though its not recommended, can I continue to run this safely?

Please suggest some solutions if necessary.

Thanks.

Why is the voltage dropping? The capacitor on the time chip has enough power to maintain time on it only. There is a small pot on the power step down module perhaps you can adjust that to get 5 v output. When the voltage is low the Arduino will not perform properly.

rogertee:
Why is the voltage dropping? The capacitor on the time chip has enough power to maintain time on it only. There is a small pot on the power step down module perhaps you can adjust that to get 5 v output. When the voltage is low the Arduino will not perform properly.

Thank you for replying. The voltage regulator on-board Arduino is leading to about 0.5v voltage drop as I observed on the VCC pin since the Arduino is powered through RAW or VIN pin.

As you state that the Arduino may not function correctly, is it possible that it may also get damaged in this setup?

Thanks.

I have gone through several posts that advocate that anything 5V regulated should go to VCC and I absolutely respect the logic behind that.

So why are you putting the 5.1 V into a different pin ?

UKHeliBob:
So why are you putting the 5.1 V into a different pin ?

Well, theoretically we can power an Arduino board through Vin, however it needs to have a headroom, say 6v? But if we apply 5v to Vin, Arduino will have less than 5v to work with, In this case, it is 4.5v. What I need to know is that do we risk damaging it? In that regard, is it safe since the rest of the modules in this setup are working at 5.1v.

Thanks.

Antrix:
As the module powers the Arduino through VIN, I observe 4.5v at VCC. There are no modules connected to Arduino on the VCC pin, although I/O functions are performed to and fro other modules with the Arduino.

The reason the Vcc voltage is dropping ie because you are feeding 5V into Vin, this needs 7V or more to give you 5V at Vcc.
Between Vin and Vcc is a linear regulator that needs over 7V on its input to give 5V out.
It is safe to connect the 5.1V of your converter to the 5V pin of the Arduino. it is built to enable you to use an external 5V supply.
5.1V is within the tolerance of the board.
Tom... :slight_smile:

You never really answered the simple direct question in reply #3.

TomGeorge:
The reason the Vcc voltage is dropping ie because you are feeding 5V into Vin, this needs 7V or more to give you 5V at Vcc.
Between Vin and Vcc is a linear regulator that needs over 7V on its input to give 5V out.
It is safe to connect the 5.1V of your converter to the 5V pin of the Arduino. it is built to enable you to use an external 5V supply.
5.1V is within the tolerance of the board.
Tom… :slight_smile:

Thanks a lot! The reason I connected the output of Step down buck convertor to Vin is because I have observed these modules to alter their voltage through the course of time, perhaps there’s something to do with the variable potentiometer. So I suspect its accuracy.

aarg:
You never really answered the simple direct question in reply #3.

The reason I stated about having read various posts that advocate supplying regulated 5v or less power supply to VCC, is that I couldn't find if there could be a damaging effect to components if done so. Also as I stated in the previous post, I have seen these type of step down convertors to vary their output over time. I don't know if this is due to the potentiometer or some other factors are involved. So perhaps I was extremely cautious :s?

Thanks.

The absolute limit the processor can take is 5.5V or even 6V (have to check the spec sheet) so 5.1V is well within spec (and that 0.1V can also be inaccuracy of your multimeter, those things are also not perfect).

wvmarle:
The absolute limit the processor can take is 5.5V or even 6V (have to check the spec sheet) so 5.1V is well within spec (and that 0.1V can also be inaccuracy of your multimeter, those things are also not perfect).

Thank you, I have connected the power at VCC. The datasheet indicates input voltage of 1.8-5.5 volts. I hope the buck convertor would hold its voltage at 5.1v as measured by the Multimeter. Yes I understand these devices may introduce their own inaccuracies in measurement, moreover the buck convertor pot was difficult to manipulate to yield an absolute 5.0v output, it was either less or more by a few millivolts, that's when I settled at 5.1v.

I think, there is no harm under-powering an Arduino board otherwise it would've been mentioned somewhere on the forum.

Thank you for support!

Antrix:
I think, there is no harm under-powering an Arduino board otherwise it would've been mentioned somewhere on the forum.

If the voltage is reduced, the maximum clock speeds are lower.

aarg:
If the voltage is reduced, the maximum clock speeds are lower.

Yes, that's what I learnt from various existing discussions. Just that there is no mention of a catastrophic component failure in an Under-volt scenario. Thank you for emphasizing about the clock speed though.

Just that there is no mention of a catastrophic component failure in an Under-volt scenario.

You never get component failure from under voltage. Electronic fact of life.

Grumpy_Mike:
You never get component failure from under voltage. Electronic fact of life.

Mike, I'm not an expert in electronics. I merely read some discussions on Arduino forums. The only probable component failure discussed was regarding MOSFET operation and Gate voltage. I could have misunderstood the discussion, so please attribute that to my lack of experience in this realm. I just wanted to be sure that Arduino is not affected by this scenario.

Thanks.

The fact that something isn’t mentioned in this forum or others definitely does not mean that it doesn’t happen. Discussions should only guide you to original sources of information.

aarg:
The fact that something isn't mentioned in this forum or others definitely does not mean that it doesn't happen. Discussions should only guide you to original sources of information.

That's what I have been asking since the first post.

I recall minimum voltage for the maximum 20 MHz clock is 4.5V, so the 16 MHz Arduino uses would need a little less.

Antrix:
That's what I have been asking since the first post.

You're asking in a forum instead of downloading the data sheet. It is exactly the behaviour I am trying to steer you away from.

aarg:
You're asking in a forum instead of downloading the data sheet. It is exactly the behaviour I am trying to steer you away from.

Please try to understand. What I'm asking does not emanate from datasheets. My question involves experience of people who have have been pationately driven by electronics all their life. The question is simple. Will the Arduino get damaged if used with 5v at VIN pin instead of VCC, while the rest of the peripheral work at the same voltage. The datasheet will not answer the query, only people who have used it in different scenarios.