Regulated Supply

I'd like to run the UNO with an external regulated 5V supply and not provide the 7-12V recommended through the power jack. I only have a 5V source available to my circuit and it is well regulated (through a 7805, capacitor, etc.). I will have no PC connected to the USB, so that's no help. How can I do this without modifying the internal circuitry (i.e., bypassing the internal voltage regulator)? Thanks in advance for any tips ...

JK

Connect to the 5V and GND pins on the power header.
This bypasses the reverse protection diode and the regulator - don't get them backwards!

I have 14 promini's at my fencing club powered this way.

jubinkiaie:
I'd like to run the UNO with an external regulated 5V supply and not provide the 7-12V recommended through the power jack. I only have a 5V source available to my circuit and it is well regulated (through a 7805, capacitor, etc.). I will have no PC connected to the USB, so that's no help. How can I do this without modifying the internal circuitry (i.e., bypassing the internal voltage regulator)? Thanks in advance for any tips ...

JK

@jubinkiaie:

You have your answer, and that's good - but my question is: Why did you have to ask this in the first place?

The schematics for the Arduino UNO is available online, and one glance at it would have told you what you needed to know. So:

  1. Did you not know that the schematic was available?
  2. Do you not know how to read a schematic?

If you answered "yes" to number 2, then I highly suggest you learn how to read schematics, as well as learn how to understand from the schematic how a device works; electronics is not a "plug and play" enivironment; knowing how to read and understand a schematic (and ultimately, how to draw one yourself), is vital to understanding electronics. As an analogy, not knowing how to read or draw a schematic, is - well - like being able to speak a language, but being unable to read or write it.

Thank you for your response, but actually I have a degree in electrical engineering, I have run my own automation/robotics company for 12 years and do know how to read schematics. From my experience, it is not good practice to inject external voltage to the output of a voltage regulator since some IC's can short out and it can destroy the whole circuit. Having just purchased the Arduino board and new to this system, I just wanted to ask someone who had experience with this to ensure that I wasn't going to blow something up. I didn't expect to get scolded for asking ...

Crossroads: Thanks for the advice. I tried it with an LM317 set at 5.04V and it works great. Reallly appreciate it. Sorry for asking obvious questions, but it is not clear from the documentation that it is kosher to place voltages at this pin ...

jubinkiaie:
but it is not clear from the documentation that it is kosher to place voltages at this pin ...

From the documentation page (http://arduino.cc/en/Main/ArduinoBoardUno):
"5V. The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply."

Looking at the schematic, it is pretty clear that 5V is being supplied to the output of the on-board regulator when powered by USB, which is just another example of "another regulated 5V supply."

jubinkiaie:
Thank you for your response, but actually I have a degree in electrical engineering, I have run my own automation/robotics company for 12 years and do know how to read schematics. From my experience, it is not good practice to inject external voltage to the output of a voltage regulator since some IC's can short out and it can destroy the whole circuit. Having just purchased the Arduino board and new to this system, I just wanted to ask someone who had experience with this to ensure that I wasn't going to blow something up. I didn't expect to get scolded for asking ...

Given that the UNO is one of a (fairly) long line of Arduinos, I would think the designers would have seen this issue long before then; still, asking isn't a bad thing, and I wasn't scolding you: First, from your post, there was no indication as to your level of experience. Most of the time when someone asks a question like this, with such little information, it is reasonable to assume that the poster is a newbie at electronics period. I made this assumption (incorrectly, as it turns out), and wrote what I did in an attempt to hopefully instill a sense of responsibility toward education for a certain type poster that I thought I was addressing. I was wrong in that assumption, obviously; my intent was not meant to scold - not in the least.

Thanks to all for helping out on this, I really appreciate the input. The next time I will spend much more time going through the schematics and manuals before I post a question. Thanks again ...