About a couple of months ago when I first had my hands on Arduino Uno, I had no idea where does that 3.3V power next to the 5V pin comes from, or more accurately, I did not really think about it until I had to make my own versions of standalone Arduinos/ATmega projects. I needed 3.3V source in addition to the regular 5V for driving some of the components. I soon realized that ATmega microcontroller does not provide a 3.3V output from any of its pins as a dedicated power source, I must create it through power circuit design. So here is my humble design. There are tons of similar materials available on the Internet. I read many of them and the datasheets, and put my understanding together in my own way, to suit my own purpose. I am sharing it here in a hope that someone as novice as myself can perhaps use it readily.

Step 1: Material needed

1) Strip board, I took a 24 strip board
2) 1 Terminal block (I took a screw terminal)
3) 1 Switch
4) 3 Electrolytic capacitors (recommended two 10uF and one 1uF, but I have used all 10uF)
5) 2 Resistors (R1 & R2, where the R2/R1 ratio should be nearly 1.64. I have used R1=1k and R2=1.5k instead of 1.64k. This is why I shall get 3.13V, not 3.3V. You can use a calculator like this)
6) 2 pin Male header (optional)
7) LM7805 5V voltage regulator IC
8) LM317 3.3V voltage regulator IC
<p>These two regulators usually go hand and hand with me and are a necessity for tons of (<em>Arduino included</em>) circuits. </p><p><strong>Good job with the strip board combo Nice neat &amp; compact.</strong></p>
<p>I would like to reference this video for help to others.</p><p><a href="https://www.youtube.com/watch?v=IjJWWGPjc-w" rel="nofollow">https://www.youtube.com/watch?v=IjJWWGPjc-w</a></p>
<p>Thank you Fearce1 for complements and also for the video link :)</p>
If you make R2 an adjustable trimpot you can get the exact voltage you want.
Oh yes, I have seen people suggesting use of pot for accurate adjustment, and variable output. I first thought I would give that a try, then backed out for apparently nothing :D Thanks pfred2.
The common value to use is a 5K potentiometer. If you get a 10 turn trimpot then you do not have to worry about it coming out of adjustment on your either. I used 10 turn trimmers on this:<br> <br> <a href="http://www.instructables.com/id/Dual-POS-NEG-Power-Supply/" rel="nofollow">http://www.instructables.com/id/Dual-POS-NEG-Power-Supply/</a>
Nicely done. A well documented and thought out project. Congratulations.
Thank you very much for encouragement.

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