Introduction: How to Build a Circuit Which Converts AC Power From a Bike Dynamo to the USB Standard

What: I will show you how to build a circuit which converts AC power from a bike dynamo to the USB standard for charing USB devices.
What will NOT be covered: Attaching and using a bike dynamo, the fine details of soldering,detailed information about electrical circuits, attaching the circuit to your bike.

Difficulty: Moderately Hard, due to soldering requirements.
 How To Solder for beginners:

Time: 1-3 hours
Required Tools/Equipment: Bike, Bike Dynamo (Bottle or Hub), Soldering iron, Electrical Solder, Wire strippers/cutters, Volt meter(Optional for testing), housing to attach the circuit to your bike.

NoteNote:  Make sure you use electrical (rosin core) solder and NOT plumbing solder.  Using plumbing solder can damage the connections and circuit components because it uses a stronger acid flux.
Required materials (I will list the part numbers which I used from Newark):
OKI-78SR-5 (7v-36v  to 5v DC voltage regulator)                                    $4.69
GSIB1580-E3 (Single-Phase Single In-Line Bridge Rectifier)                  $2.11
2222 021 16682(25v 6800 microF capacitor)                                         $5.83
2222 138 36109 (25v 10 microF capacitor)                                           $2.08
292303-1 (USB type A receptacle)                                                      $1.51
VECTOR ELECTRONICS – 8001 – PCB (Printed Circuit Board)            $25.66
WH18-00-25 (Hook-up wire 25FT 18 AWG)                                           $5.57
                                                                                       Shipping:     $10.00
Total(Without Tax):    $58.66

Why: Imagine yourself cruising along on your bike and suddenly you get a flat.  You pull off to the side of the trail and start rifling through your saddle pack to grab your  cellphone and call for back up, but you discover that there is a problem, your phone is dead. Now you are stuck and the only thing you can do is walk to the nearest town, luckily it's only 10 miles away.  Now lets imagine a situation that is even worse than that, you are a cruising a long and your tunes cut out.Your iPod has died, and you were only half way into your ride. You cannot stop now but there is no music to keep you going, this is a problem.  What a nightmare that would be.  Now lets imagine that you had some mystical device, from the heavens themselves, which could power any USB device that you own. 

Disclaimer: I am not an electrical engineer, and this circuit has not been tested due to my soldering failures.  This is merely a DIY work in progress that I am posting for feedback and future improvements.
CautionCaution: Use at your own risk!

Step 1: Obtain Parts

As listed in the introduction I obtained my all of my circuit components from The reason I did so online is because a lot of these components cannot be found locally, so be prepared to order online and pay for shipping.  There are other sites online that will offer the same parts, but I chose Newark for price and availability. The first thing you will need to do is get online and order the circuit components from the site of your choice.  If you goto you can follow this list:

OKI-78SR-5 (7v-36v  to 5v DC voltage regulator)                                    $4.69
GSIB1580-E3 (Single-Phase Single In-Line Bridge Rectifier)                  $2.11
2222 021 16682(25v 6800 microF capacitor)                                         $5.83
2222 138 36109 (25v 10 microF capacitor)                                           $2.08
292303-1 (USB type A receptacle)                                                      $1.51
VECTOR ELECTRONICS – 8001 – PCB (Printed Circuit Board)             $25.66
WH18-00-25 (Hook-up wire 25FT 18 AWG)                                          $5.57
                                                                                       Shipping:     $10.00
                                                                         Total(Without Tax):    $58.66

Caution Caution: circuit components can be fragile and vulnerable to Electrostatic Discharge. Avoid working with components on surfaces such as carpet. 

Step 2: Understanding the Circuit

It is my belief that an understanding of what this circuit is doing is important to successfully assembling the circuit.  The reason I believe this is because if you know how things are working, you are more likely to understand how they come together.  This will help prevent you from missing mistakes that you may make in the next step.

The first thing that you need to understand is that a bike dynamo will generate AC(Alternating Current) power. We cannot directly use this power to charge/power our USB equipment because digital equipment almost always uses DC(Direct Current) power. In fact, for any USB port there are standard specifications which must be met to make it a USB port. Direct Current at five volts is the current USB standard; however, the current supplied by the port may vary depending on the device connected to it.

The second thing to know is that the voltage and power output of the dynamo will vary with the rotation of the generator itself.  Since the generator spins synchronously with the wheel of the bike, the faster you go the more power is generated at higher voltages. As stated above the USB standard is 5 volts, so we must find a way to regulate the incoming voltage.
CautionCaution: Failing to regulate voltage may damage any USB device that is connected to the unregulated source.

The final thing to be aware of is that the current output of our circuit will also vary.  Most devices will only draw the current that they need so this should not be an issue; however, there are some devices that may be sensitive to the amount of current output. 

CautionCaution: Use this circuit at your own risk, it could potentially damage sensitive electronics!


Step 1: Convert AC to DC using the GSIB1580-E3 (Single-Phase Single In-Line Bridge Rectifier)

Step 2: Use the 6800 microFarad capacitor to smooth out the power.  This step is needed because after you do step 1 you will have a DC power source but because the AC power was alternating, the DC power given will have humps that go from 0 to peak voltage and back down again.  The capacitor will charge as the voltage rises, and it will feed power to the circuit while the voltage drops, thereby giving a steady voltage. See Diode Bridges for a more detailed explanation.
NoteNote: The capacitors will be connected in parallel with the rest of the circuit.

CautionCaution: Electrolytic capacitors (the ones used here) have negative and positive terminals.  The negative terminal will  
be connected back to the negative terminal of our diode bridge.  The postive terminal will connect with the next            
component in line.

Step 3: Use the OKI-78SR-5 Voltage Regulator to bring the varying DC voltage (8.4-25V) down to a steady 5 volts.

Step 4: Use another 10 microFarad capacitor to again smooth the power output from step 3, as there may be slight variances from using this device.

Step 5: Connect the USB A receptacle such that the pin 1 is connected to the positive DC lead, and pin 4 is connected to ground(or the -terminal of our bridge rectifier).  See  to see how the pins are numbered.

CautionCaution: Do not reverse the ordering of the pins (connecting pin 4 to +5V dc and pin 1 to ground).  Doing so may cause harm to the plugged in device!

Step 3: Place Components Onto the PCB and Solder in Place

Understanding the board:
When you receive the PCB (Printed Circuit Board) you will notice that the particular board that we using has sets of 3 holes connected with each other.  These groups are separated from the rest of the board.  There is also a large interconnected area that separates those columns. The reason these pads are set up in such a manner is to allow you to connect certain component leads together, while keeping them separate from others.  For example, with a capacitor you do not want both the leads to be on the same pad! The capacitor will not charge because it has been shorted out. What you would do is connect the positive terminal to one pad, and the negative terminal to a pad that is connected to ground.  Since there are a few things in our circuit that need to be connected to ground, we will ground the main area of our PCB.

Step 1: Place the bridge rectifier on the PCB so that the 4 leads are all on separate pads, with one of the middle leads connected to the main area. See the attached image for reference.

Step 2: Cut two peices of hook-up wire from your spool. You will want to leave yourself about 2 foot pieces, long enough so that you can hook them to wires from your bike dynamo without yanking on your finished board. Strip one end of each wire.  We will be using these wires as the AC connection to our circuit.  Notice the bridge rectifier has two connections for AC, they are in the middle and labeled with a wavy line(that stands for AC). After you have the pieces cut, feed one of the stripped wire ends through the top(non-metal) side of the board and make sure it comes out of a hole within the main area, we will make this ground.  Label that wire with a piece of colored tape or some kind of marking. Feed the other wire through a hole that is connected to the other middle lead of the rectifier.  

Step 3: Notice in my image referenced in step 1, the two outside leads are both on their own strip of three. These leads are the positive and negative DC terminals and they are labeled with a + and - sign for each respective terminal.  Find the pad that corresponds to the positive terminal. Take the 6800 microFarad capacitor and drop the positive terminal of the capacitor through a hole that corresponds with the same pad as the positive terminal of the rectifier (so they can conduct). Align the negative end of the capacitor so that it connects to the pad which has the negative rectifier terminal. It may be handy to use a piece of wire to connect a few pads to the negative rectifier terminal because there will be multiple connections leading back to it.
NoteNote:Switching the terminals of the capacitor (positive and negative) will cause the capacitor not to charge and will make this circuit non-functional.  Make sure you figure out which terminal of the capacitor is negative and which is positive.
The 6800 mF capacitor has arrows pointing to the negative terminal.

Step 4: Now find the OKI-78SR-5 voltage regulator.  Notice that it has three terminals, the far left(with the hexagonal black piece facing towards you) is DC current in (+), the middle terminal is to be connected to ground (main area), and right terminal is the  DC out(-).  You will want to align the regulator so that each terminal has its own respective pad.  Use small pieces of wire to connect the positive terminal back to the positive terminal of the 6800 microF capacitor and the middle terminal to the main(ground) area of the board.

Step 5: Now connect the positive terminal of the 10 microF capacitor to the same pad as the negative terminal of the voltage regulator. Connect the negative terminal of the 10 microF capacitor with the negative terminal of the rectifier, just as you did with the first capacitor.

NoteNote:Switching the terminals of the capacitor (positive and negative) will cause the capacitor not to charge and will make this circuit non-functional.  Make sure you figure out which terminal of the capacitor is negative and which is positive.
The 10mF capacitor has a black stripe closest to the negative terminal.

Step 6: Locate and examine the USB A receptacle. Notice that it has 4-pins connected to it, the middle two are data pins which we will leave disconnected.  The outside two are our DC power pins, pin 1 is +5DC and pin 4 is ground (DC -).

                                                                                            USB A Receptacle Pins:
USB pinout
Notice that with the connector facing towards you pin 1 is in the far left; however, if you were to turn it around it will now be on the right.  This is the pin (pin 1) that you want to connect with the positive terminal of the 10 microFarad capacitor. Pin-4 is on the far right if the connector is facing towards us, but on the left if it is turned the other direction. Connect this pin back to the negative terminal of the rectifier.

CautionCaution: Reversing the connection of Pins 1 and 4 may cause harm to the USB device connected to this circuit.  Pay close attention to these pins and double check that they are correctly connected!

Step 7: 
Once the components are set in place you should follow your way through the circuit and ensure that everything is in the proper place.  A good way to do this is to act as if u were the current and start from the beginning.  Once you have double checked all of your connections you may begin to solder. Keep in mind that soldering is really an art and you should practice soldering until you are confident before you begin work on this project. I do not cover proper soldering techniques as it is out of the scope of this project.

Step 4: Conclusion

As stated in the introduction my initial attempt at completeing this circuit was not successfull.  This was completely due to improper soldering equipment and lack of soldering experience.  This is why I cautioned many times throught this instructable that soldering experience is a must.

Assuming that all went well for you, you will end up with a circuit about like the one attached to this slide.  Mine has many more wire leads because I needed to fix many initial soldering problems so do not worry if it does not exactly match up.  You may want to test this circuit prior to plugging any cellphone or sensitive device into it.  To do so:
Step 1:Get a volt meter and set it to 20 v DC test mode.
Step 2: attach the red lead to pin one of the USB receptacle. 
Step 3: attach the black lead to pin four on the USB receptacle.
Step 4: Observe the voltage as you turn the pedals on your bike.  The voltage should stay steady around ~5v.  If it is not, it is not safe to plug in you USB device! You may re-check connections and re solder as needed.