About: Space Monkey Pirate Robot

(Yet Another 9 Volt USB Charger)

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Step 1: Parts and Testing.


5v regulator (Lm7805)
Female USB port
Braided wire (20g)
Used 9v battery (Walgreen's brand)
5 minute liquid epoxy
Non-conductive epoxy putty

The circuit design is from http://ipod.hackaday.com/entry/1234000270029372/ All I did was add an LED so I could see if the battery was good. He's got nice diagrams of the USB and regulator to help you wire this together.

Step 2: Disassemble the Battery:

Pry the metal lip back from the bottom of the battery and straighten the edges as much as possible with pliers. Carefully pull out the plastic base and save. After that the innards should slip out without much trouble. Cut the negative lead going down the side and save the connector. Save the case.

I chose to use a Walgreens brand battery because it has nice thick plastic on the top and bottom. Duracell uses paper.

Step 3: Solder the Circuit Together:

For the USB I just drilled three holes in a row and cut out the rest of the rectangle with an Xacto knife. The USB should be mounted in the plastic before you solder the connections.

So the USB, LED, and resistor are on top and the regulator is on the bottom. The wire lengths are just to have enough room to epoxy the top in before the bottom, 2"-3".

Step 4: Prepare the 9v Case:

Sand the paint off the case with 400 grit sandpaper and rubbing alcohol. Carefully epoxy the LED and USB to the plastic base. Just use enough to tack it in place, don't get it in the USB.

Cut the case at about the 2/3 mark.

Score the inside of the case with a file or an awl to give the epoxy some kind of mechanical hold.

Step 5: Epoxy Putty the Top:

Put just enough epoxy putty to cover the components on top. Don't put it all the way to the edge, you want it to fit in the case.

Once the epoxy putty has cured (not fully, just enough that it doesn't deform when you push on it), put the top half into the case and seat it against the lip. While holding it against the lip drip a small amount of liquid epoxy around the edge to hold it in place.

After the top is held in place fill the remainder of the case with putty, leaving just enough room for the bottom to be pushed in. Push the wires into the case and force the top into the putty 1/16"-1/8" past the edge of the case.

Step 6: Close the Case:

While the epoxy starts to harden, cut 1/8" slots at each corner to help them fold over. When the epoxy has pretty much set up bend each edge over to close the case. Burnish or sand any sharp edges.

Step 7: Finished:

Test with a multimeter before plugging in your USB powered device.

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378 Discussions


3 years ago

what type of resistor is it

Please change the title! This was an awesome tutorial but, it took me forever to find it because the title was confusing. Had it not been me searching on google images for it, I would not have found this.


4 years ago on Introduction

Nice idea for the housing of it, but I always wonder how much capacity a simple 9v batterie shall have. I would rather put the transformer on a batterieholder containing AA or bigger primary cells.


4 years ago

i have some problem in making the circuit how can i fix it..??? tried it twice with new parts but doesnt work..

i think it wil damage cell phone coz cell phone need 4 volts and it supliies 9v??
can resistors decrease the voltage?
please rply someone

8 replies
swestonPranjal Joshi

Reply 5 years ago

your right that's is why you use a +5V fixed voltage regulator (7805) between the battery and the female usb and led.

Pranjal JoshiCekpi7

Reply 7 years ago on Introduction

i made a project same to it..
but aftr charging my cellphone shows "bad contact of charger".. so wat can i do to repair dat??

Pranjal JoshiCekpi7

Reply 7 years ago on Introduction

i chkd usb cable..
der is no fault..
n i nt yet got a multimeter to test output voltage.. :(
did u mean for 1st few mins. the voltage is more than 5v bt den it decreases below the minimum charging capacity of battery hence it shows bad charger contact????
if yes then wats the solution on it..

Roshy10Pranjal Joshi

Reply 7 years ago on Introduction

you can get 2 100k ohm resistors and put one from positive to pin 2(data) and the other from pin 3 to positive(data) this will trick you phone which probably is realy trying to say "I'm not connected to a computer so I refuse to charge" (because it might be too many volts and over charge you phone.)


Reply 8 years ago on Introduction

It probably could, but I would not recommend it. That 7805 regulator is rated for 1 amp, and is going to get dangerously hot, even with a heatsink, burning off 4v of power to regulate 9v down to 5v. Not to mention that a linear regulator is TERRIBLY inefficient in this particular instance. A better option would be a switching regulator such as this one:

The switching regulator is still extremely small, and would easily fit if you left the casing only slightly longer. Also, switching regulators don't burn off the excess voltage, but instead use pulse. By turning the flow of current on and off VERY quickly, it simulates lower voltages. A linear reg gives you about 55% efficiency, whereas the switching reg gives you close to 90%, which means that battery will last longer also. Not to mention the added safety because that switching reg is rated up to 10 amps.


Reply 7 years ago on Introduction

You forgot to mention the addition of a needed 1k ohm resistor to the data pin on an iphone charge plug. Without it, it won't charge.