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We are making a circuit which harvests power from an audio jack.

The growing prevalence of smartphones, even in developing regions of the world, means that using an audio jack for power could meaningfully impact individuals the world over by providing a small source of DC power.

Step 1: What You Need

Tools
Oscilloscope & lead wires
Device that plays audio and takes microphone over a 3.5mm audio jack (we are using a Samsung Galaxy Vibrant).
Breadboard
LCR Meter

Parts
3.5mm TRRS Audio Cable (1)
Varied values of resistors, between 1Ω and 15 kΩ
1.5 mH inductor (1)
Schottky diodes (4)
Magnet Wire

Assumed Knowledge
You can use a breadboard. If you’ve never used one before, see http://www.instructables.com/id/Breadboard-How-To/.
You can use an oscilloscope. If you’ve never used one before, see http://www.instructables.com/id/Oscilloscope-How-To/.

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<p>Nice instrcutable. I also liked this video here, it uses no transformer, just schottky diodes and a voltage multiplier:</p><p>https://www.youtube.com/watch?v=7C6z_xCyqG4</p>
<p>I am still not very sure about how to choose the smoothing capacities. The link you provided teaches us to calculate a capacity based on frequency and R_load. But how to calculate the other two capacities you illustrated in your circuit?</p>
<p>well stick to portable chargers or keeping fully charged batterys long car rides to places</p>
<p>well stick to portable chargers or keeping fully charged batterys long car rides to places</p>
<p>well stick to portable chargers or keeping fully charged batterys long car rides to places</p>
<p>well stick to portable chargers or keeping fully charged batterys long car rides to places</p>
<p>I don't see where you added the 1.5mH inductor onto the circuit... Or did you use the inductor to make the 1:20 transformer? </p>
Replace the silicon diodes with germanium ones. You will lose only about 0.2V instead 0f 0.7V per diode.<br> <br> Use a center tapped transformer (see <a href="http://en.wikipedia.org/wiki/File:Fullwave.rectifier.en.svg" rel="nofollow">here</a>) You need twice as much windings, but there is only one active diode, so you'll lose only 0.7V instead of 1.4V (or only 0.2V with germanium diodes)<br> <br> Or... switch of the smart phone, open it and take out the accumulator. Voil&agrave;. Stable DC voltage with very low impedance! (Of course, you can't surf the internet any more...)
Airplane power? :o

About This Instructable

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Bio: A maker, addicted to sewing, cooking, and crafting. Sometimes an engineer. Spent a summer at Instructables; got a degree in E: Neural Engineering at Olin ... More »
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