USB Voltage and Current Tester!! (version 2)




Introduction: USB Voltage and Current Tester!! (version 2)

About: Ex-Navy Gunner Learned to repair I.T. equipment because nobody local knew what the hell they were doing!


Since it's sometimes necessary to check your USB ports for voltage or if you are curious on what kind of Current draw your devices might be pulling, it would be great to have something to check these.

Now you can.

Instead of just hacking apart USB cables and checking these readings with a Multimeter or one of the Pen Drive style voltage checkers, this instructable will give you a tool that is painless to use.

Moving onward.....

The old version of this was OVER 13" in length with the cable, this one is only 2 1/2"!!

*NOTE: I am not using the 2 DATA wires AT ALL!! There have been some comments to use it, but if using this adapter on a HD or FLASH Device, using the DATA lines and disconnecting power frequently could/will corrupt your DATA or Filesystem.


Thank you!!!

Step 1: Parts!

First we will need a few things:
1. A Flash Drive case (or something equivalent, I used a USB Bluetooth dongle)
2. Sturdy Paperclip, maybe two
3. Wire
4. A Male and a FEMALE USB connector. I got the MALE plug from an old 128MB Flash Drive a co-worker donated to the cause (THANKS GARY!)
5. a small SWITCH from an old Flash Drive
6. Adhesive of your choice (I'm using Epoxy Putty and Epoxy again for this one
7. Spray paint of your choice to make it a little prettier (I use Duplicolor for Plastic & Vinyl)

Step 2: Step 1!!

Ok, dismantle your "sacrificial" drive or peripheral.

Let's wire the SWITCH!!

Solder ONE RED wire to the MIDDLE contact and ONE RED wire to the contact on either side.

Place the SWITCH on whatever side of the casing you desire and either use a hobby knife or a dremel to remove enough plastic to allow the SWITCH to be installed.

You will want to GLUE it into place, even if it's temporary.

Step 3: Step 2!!

Now to prep your USB connectors.

I just went ahead and pulled the "legs" I didn't need out of the connector.

I bent the outside pins so that the connector would sit better in the plastic case and make it a little easier for soldering.

Sorry, I forgot to take pics of the MALE USB connector.

Solder a RED wire to PIN 1 and a BLACK wire to PIN 4 on BOTH connectors.

If you don't know which is which, go here:
Scroll down to the section titled USB Cables.

After the wires are soldered, you will want to secure them to the case using adhesive.

Step 4: Step 3!!

Now we want to bend the paperclip into small loops using either a ballpoint pen and a pair of pliers or whatever will help you make loops.

You will need to cut and bend the wire to make a "U" shape, you will need 3 of these.

I cut a hole in the casing using a dremel to accommodate the FEMALE USB connector.

Using a drill, make the holes for the wires.

Step 5: Step 4!!!

At this point, it might be easier to paint the cover before pushing the wire through.

Step 6: Step 5!!

Now here's the fun part (pain in the butt)

Let's get this bugger soldered!

Ok, the RED wires from the SWITCH, ONE red wire goes to EACH of the loops for the POWER side (the side with TWO loops)

The RED wire from the USB MALE connector goes to the end of the closest loop to it.
Same principal applies for the FEMALE USB.

Here's a picture I cobbled together (please don't comment on it, I already know that its HORRIBLE!)

Do NOT use the pic as a reference for PIN 1 & 4! The first time I put it together I had one of them switched, just use it for reference only.

Once it is wired, TEST IT!!!!
The switch should allow you to switch between measuring VOLTAGE and CURRENT.

You might want to label on the bottom of the device which position does what.

Like before:
For Voltage, the RED lead from your multimeter to either of the TWO loops on one side.
Use the BLACK lead on the SINGLE loop.

For Current: move the SWITCH, and put the BLACK lead on only ONE of the TWO loops on one side, and put the RED lead on the other of the TWO loops.

Step 7: Finally!!!

At this point, after I insured that it worked, I filled the case with EPOXY and called it a day.

The only thing I will be adding to it is to make it look a little better or paint something on the bare spot on the top!

There you have it guys, Happy FESTIVUS or whatever you do for holidays!!!

1 Person Made This Project!


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6 years ago

Never needed something like this until today - a gr8 item and it works terrifically!!

However, I'm getting a bit too much arthritis in my hands to do this kind of detail work so it took me the better part of the day to get it completed - never did find my little 'clip stands' that I used back in the 60s & 70s to hold the small pieces while soldering!! ;-/


7 years ago on Step 7

What do you need the switch for cant u just leave it out?

I know it's been a while since you posted this, but I want to know is where did you get that switch from? I like how small and practical it is, but I can't find a similar one.


11 years ago on Introduction

This is a cool idea! I was looking for a way to check how much current an Arduino project was drawing, and your first version inspired me to make my own testing cable.

I made it much smaller than this though - I cut open an extension cable, cut the power line, then soldered a 2-3 cm wire to one end to extend it a little, and soldered each end to a 2-pin header and insulated the solder points with heat shrink tube. Then I stuffed most of it back into the cable body, and slipped a jumper - the type with the "handle" and visible metal loop - onto the header. (and then spent about 5 minutes continuity testing various combinations to be sure I wasn't shorting power to shield...) Now, to test current, I clip my probes onto the bare header so I don't lose my connection when working with things like flashdrives or smart devices like phones - if the probes short, no big deal, it'll just read "0," though insulated clips work just fine to stop that. Then, to test voltage, I disconnect the device, slip the jumper on, reconnect, and stick one probe into the hole on the jumper, and the other onto the shield of the USB cable - as long as your hub properly grounds the shield, I think it should read the same as the normal 5V to GND pin - it has for me when disconnected, and I've seen voltage drop on some devices with it.

I left the data lines intact, so I can see things like current draw when writing to a flashdrive, and in different device states, though the iPhone still realizes something is fishy and says charging isn't supported by the device when I'm in current measurement mode. My multimeter isn't top of the line though, and I wonder if it's impeding a little too much...

Anyway, thanks for the inspiration - this is really handy for debugging a USB device in progress when I'm not sure how much room I have to work with power-wise! I could put up a spinoff tutorial if you like?


Reply 11 years ago on Introduction

Sorry, seems I missed a step. The usage is similar to the original project, except with this version, we have a switch and not a binder clip.


12 years ago on Introduction

You Rock! This beats the h##l out of trying to use the multimeter straight to the computer. This is a definite build for me. Thanks for sharing.


13 years ago on Introduction

cool. I just made a usb christmas tree (I have an ible about it (that wasn't spamming bacause it relates(oh look, three parentheses))) and I just had to assume that there were 5 volts. this might have helped.


13 years ago on Introduction

OMFG!!!!! Can I BUY ONE!? I LOVE IT! If it's not available for sale, can I send a few bucks to a PAYPAL to donate to "the cause"? You have come up with some really cool stuff and I think it's worth buying ya a BEER!!!