How to power board

Projects General Guidance
1

hey everyone

I have an Arduino Uno R3 https://store.arduino.cc/usa/arduino-uno-rev3

Im making a project that interprets voltage data from an oil temperature sensor in a car, to display on a screen, amongst other things. I already have another Arduino established in the car for another purpose, which is powered through its Vin and Gnd pins, which are connected to the positive and negative wires of a 5v voltage regulator connected to the 12v cigarette socket. Works great.

I've been hoping that I could use the same regulator (has a max output of 3,000ma) to power the Uno, but the problem I've encountered is that the documentation for the board states its Vin accepts a voltage of 7-12.

Of course I could wire the voltage regulator directly to the Uno's 5v pin, but I fear that as the car's voltage fluctuates between 12 and 14 volts, the 5v supply from the regulator may be unstable and I would like to retain the use of the Uno's onboard regulator.

Another option is using the USB input and splicing the 5v regulator's output into a USB cable and powering it that way, but the problem with this is I'm not sure if this uses the Uno's onboard voltage regulator or not.

Lastly I thought that If i could somehow step down the car's voltage from 12 to 7 volts, it could then theoretically stay between 7 and 12 volts as the car's voltage fluctuates, and I could then power the board through the Vin, but with my limited knowledge of electronics I'm not sure how to do it this way.

Frankly I'm a bit confused and I'm not sure what is the safest way to power the board. Any guidance would be appreciated.

2

The purpose of your external regulator is to provide a stable 5V.

Feeding the 5V into Vin is incorrect. Did you ever measure the 5V output of the Arduino when using that setup?

3

Hi,
Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html .

A diagram of what you are trying to accomplish may help, a picture of a drawn diagram would be good.

Thanks.. Tom.. :slight_smile:

4

sterretje:
Feeding the 5V into Vin is incorrect. Did you ever measure the 5V output of the Arduino when using that setup?

Thank you for this, it seems I have made an oversight as I replaced my other arduino which used to be a Nano clone, to a Nano 3.0 as I broke it accidentally, and I didn't in fact check how to power it! It does say that 5v is too low for the Vin, but nevertheless it seems to be working as intended thus far :P. No i haven't measuired the 5v output but i definitely will now.

TomGeorge:
A diagram of what you are trying to accomplish may help, a picture of a drawn diagram would be good.
Thanks.. Tom.. :slight_smile:

Well here is an image of the Uno R3 board in question .
I'm not sure what I would put in a diagram - I understand how my circuits are going to work perfectly, that's not the issue - I simply lack the understanding of the best means to provide a voltage to to the board and what amount of voltage.

5

Regulated +5VDC to the pin marked 5V Power Pin. This is the output of the on board voltage regulator