5V on 5V pin or VIN

Development Tools IDE 1.x
1

Hello

I know this question is far from original and I have read a lot of answers to similar questions. But the answers differs wildly.

I do not want to rely on the Arduino's in-built regulator only because it would need to supply 5V(likely around 300mA) to other components as well and it would have to step down the voltage from 14V. I need 15V because on of my components need 14V. So I am using a LM2596. I just cannot decide whether to put 5V on 5V pin or VIN.

Pros and cons to putting 5V on VIN:

  • Increases protection in case of the LM2596 failing unsafely.
  • Increased protection when connecting USB while also having 5V on VIN.
  • Only around 4.0-4.2V after the in-built voltage regulator

Pros and cons with 5V on 5V pin:

  • 5V for the Arduino microprocessor
  • No protection in case of the LM2596 failing unsafely
  • No protection when connecting USB while also having 5V on VIN(although I have done that before without issues).

I really would like to use VIN but the low voltage is a concern. However I did a (very unscientific) test and put a "LED blink" sketch on the Arduino and powered it externally through the VIN. Then I lowered the voltage until I could see the LED blinking irregularly. I had to lower it lower than 3V, almost down to 2,5V before I could easily "see" the microprocessor struggling. I know problems can occour way before I can see it with my eyes(likely especially with serial communication etc.) but still 2,5V volt is far from 4V.

So would I be crazy to ignore the "theoretical" problems with feeding only 4-4.2v to the microprocessor and enjoying the benefits that VIN gives?

/SeaAnt

2

Yes, but you should first check that how much voltage the microcontroller recieves when you connect 5v to the VIN. Measure that voltage and consider what to do next.

.. Arnav

3

Thanks for the reply Arnav

I believe that I did measure the voltage going to the microcontroller as i meassured the voltage on the 5V pins(so after the arduino's voltage regulator) when power was supplied on the VIN(before the arduinos voltage regulator). To my knowledge the voltage on the 5V pins are the same voltage that the microcontroller recieves.

/SeaAnt

4

seaant:
Thanks for the reply Arnav

I believe that I did measure the voltage going to the microcontroller as i meassured the voltage on the 5V pins(so after the arduino's voltage regulator) when power was supplied on the VIN(before the arduinos voltage regulator). To my knowledge the voltage on the 5V pins are the same voltage that the microcontroller recieves.

/SeaAnt

So the obvious answer is to use the VIN pin. The microcontroller would have no voltage problems. It would work like normal.

..Arnav

5

ArnavPawarAA:
So the obvious answer is to use the VIN pin...

Another bold statement from you there.... Seems you are willing to help everywhere but it seems you very often fail to provide good guidance. It appears to me after reading some of your affirmative answers / bold claims that you lack the relevant knowledge and/or hands on experience. Can I ask you to please adjust your recommendations to things you've tested, you know are true or provide context and documentation supporting your claims ? That will help keep the forum a place where good information is shared.

To the question, there is nothing obvious as an answer and @seaant initial pros and cons are well researched. I would say that I've seen more than one cheap adjustable LM2596 fail miserably overtime esp. if deployed outside where moisture can impact the potentiometer (favor those with sealed potentiometers, not those with the very small metallic ring).