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Many of us have surplus 5 volt AC/DC chargers for cell phones we no longer use. Those chargers could be useful for a variety of power sources if there were a way to attach a female USB connector to the cord and do it for little or no cost. But, stores like Radio Shack do not list a female USB connector in their on-line inventory. USB cords with a female end are expensive unless you happen to have a non-working USB cord with a good female end. Improvising one's own female connector becomes an attractive option and others have done that. But, the base material for a connector needs to be quite sturdy, thin enough, and there needs to be a way to attach thin circuit traces. This Instructable is an approach I attempted. It worked with some devices, but not with others.

The photo shows the female USB connector on a car charger for a USB device.

Step 1: Tools and Materials

An almost ideal material for a female USB plug that connects to a male USB cord end is an old circuit board from a defective computer power supply or some other defunct piece of electronic equipment.

Materials
  • An old circuit board
  • Solder
Tools
  • Low wattage soldering iron
  • Dremel with a cutting wheel
  • Sandpaper
  • Drill and bit

Step 2: Safety Concerns

The photo shows one of four 220 volt 820 micro-farad capacitors inside my old computer power supply. These capacitors hold a charge long after AC power was last applied to the power supply. PC guru Scott Mueller (Upgrading and Repairing PCs) tells his readers never to open a computer power supply because of the lethal charge of electricity stored by these capacitors. I cautiously opened the power supply case and visually located the capacitors. I determined which pins on the circuit board were connected to these capacitors. Then I shorted the pins on each capacitor with a screwdriver as shown in the photo. The screwdriver has an insulated plastic handle. Shorting the capacitors removes the charge they hold. In my experience it is good to short each capacitor three or more times to be certain the capacitors are fully discharged. Then it is safe to handle the circuit board and to desolder parts from the circuit board. 

Step 3: Cut a Suitable Section of the Circuit Board

There are four circuit traces inside a USB connector, whether male or female. The two outermost traces in any USB connector are the power connections. On center these outermost circuit traces appear to be 7.2mm from one another. Look for traces on the power supply circuit board that are very close to that same dimension apart from one another. Failing that, it would be possible to use an area totally covered with one large circuit trace. Later the copper material could be ground away where it is not needed. This would make two circuit traces exactly where you need them. 

I used a Dremel tool with a cutting wheel to cut away a portion of circuit board with two suitable circuit traces. I cut it larger than necessary so I can trim it more precisely later.

Step 4: Trim Component Sealant

This part of the circuit board held the large capacitors shown in step 2. A sealant was used on the board, perhaps to keep the capacitors from vibrating and making noise. Trim it away clean with a knife.

Step 5: Desolder Any Components

A small capacitor still needs to be removed from the section of circuit board I am using. I am using a 15 Watt soldering iron to desolder the remaining part.

Step 6: Other Preparations

The side of the circuit board with the traces also has a small surface mount diode that connects the two traces. I was not able to desolder it, so I used the cutting wheel on a Dremel tool to break the connection from the diode to one of the traces. Notice the tan color where there should be green.

I also used my soldering iron to smooth bumps in the solder on the traces. 

Step 7: Trim the Circuit Board to Fit a Male USB Connector

Here you see the circuit board portion aligned with the opening on a male USB end. The red lines indicate the position of the traces in the male end. This picture gives an idea of how much of the circuit board needs to be removed on each side. (In use, the circuit board will be inverted.) I can use the face of a cutting wheel in a Dremel tool, but will need to be very careful and check my work often.

The photo shows a USB extension cable with a good male and female end. I want to save this for its original purpose and do not want to take an end from it.

Step 8: Preliminary Fit

I have a good preliminary fit. The circuit board portion fits nicely into the male USB end. In places, the solder presented too much thickness. I turned the circuit board face down on a piece of very fine sandpaper resting on tabletop and made a figure 8 motion to sand the solder to a uniform thickness that fit. Just to be safe, I want to remove whatever is necessary to prevent a short to the inner traces inside the USB connector. 

Step 9: Raise the Traces for Better Connections

After some experimentation, I found I needed to make the traces a little elevated above the circuit board. The easiest way to do that was to lower the circuit board material by grinding it away with a cutting wheel on a Dremel. This also allowed me to narrow the traces for a better match with the traces in the male end. In the photo you can see the beige colored board material that appears when the green surface coating is ground away. You can also see the proper polarity for the male USB connector. The red (+) wire goes to the left side as shown and the black (-) wire goes to the right side. 

And, I drilled two holes in the circuit board material to make a strain relief for the cable. The cable goes down through one of the holes and up through the other. Then the bare ends are soldered to the traces.

Step 10: Connecting the Ends

I inserted my new female end into a standard male USB end. The fit was a little loose so I used some folded paper to make it more firm and the contact more certain. 

I wish I could say this works in every situation. It worked well with one USB device I have, but did not make adequate contact on another for which I really wanted to use it. Perhaps I need to make the traces more precisely fitted to match their counterparts in the male USB connector. Still, this may work on an application you need and may be worth a try. 
<p>Seriously? You read Scott Mueller?</p><p>Ok so now everyone knows you are a genius lol ;)</p><p>Good work here by the way.</p>
Thank you. I once picked up a copy of the 13th edition of his &quot;Upgrading and Repairing PCs&quot; on a sale table after the 14th or 15th edition had been published and decided to read it cover-to-cover. I learned a lot of things, but did not understand everything. Later I bought a copy of his volume on repairing laptops and read it cover-to-cover, too. The 'genius' label might be appropriate if I had understood everything.
<p>pssst</p><p>I read them as well and didn't understand it all either lol.</p><p>But even so. Just being able to read those tombs is enough to say congrats to. :)</p>
<p>can i connect it to usb dc dc step up converter? </p>
I suppose you can. It needs to be made so it connects in a reliable way.
Phil, while going thru my box of spare computer gadgets, I found several of these female USB connectors. They are used to connect to a five pin something-or-other, but I have never needed them. I plan to find which two of the five pins go to the + and - connections on the USB side and solder them to the 5v cell phone charger wires.
Bill, <br><br>One of my steps shows the correct connections and polarity. The power terminals are the outermost strips. Imagine your connector without the shroud, the brass strips facing you, and the front end pointing upward, the + or red will be on the left and the - or black will be on the right. You can also find polarity diagrams for various USB connectors on the Internet. A 5 volt power supply for general use can be very handy.
Thanks Phil, I needed that info.<br><br>Have already used my only old 5v cell phone charger, will make a trip to the local Goodwill to find another.
Thanks Phil, I had the need to make a similar connection, see my Instructable: https://www.instructables.com/id/Make-a-great-little-book-light-from-recycled-elect/ <br> <br>My Instructable mainly explained, as you did, that the voltage supplied from many cell phone chargers and the voltage from USB is the same, 5 volt DC, so you can interconnect devices. But what I lacked was a good way to connect them. You provided that!
Thanks, Bill. I like your book light. I wish I could say my USB connector from part of a circuit board worked perfectly in all applications. For a long time it has seemed there ought be something that could utilize old circuit boards.<br> <br> I was in the nearest Fred Meyer store a couple of days ago and just outside the electronics department I saw a USB port with one male end and four female ends. It looks a little cheap, but functional. The price is under $7 and the female ends have short wire leads on them that beg to be cut and soldered to something else.<br> <br> Did you see my Instructable on the <a href="https://www.instructables.com/id/Ramps-for-a-Low-Car/" rel="nofollow">homemade car ramps for a low car</a>? I included a pressure switch operated by the front left tire. The switch turns on a 5 volt flashlight bulb resting on my lap or the shift console. It is powered by a phone's car charger.
Nice improvisation! That reminds me the way I used to improvise a serial cable for my Garmin GPS device from a plastic credit card and a serial cable ended with DB9 connector.
Thanks. I have usually thought of old circuit boards as waste. Something like this can give parts of them a new life. Your Garmin cable sounds interesting.
A good job, Phil. I love your creative solutions. Another good source for female USB connectors is old system boards.
I stopped at a computer repair shop and asked if any old boards with a female USB connector were available, but, they said they had none. I did find a short USB extension cable for under $5, which is not too bad. Thanks for looking and for commenting.

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Bio: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying ... More »
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