When you solder as sloppily as me and use solder in excess, you sometimes need the epoxy! :)

Thnx!!!

Posted at 12:04 pm on Dec 17th, 2008 by Vincent (gmgfarrand)

Hmm, this hack could be a bit better… first of all, it would be more useful to connect the datalines too, for a device like a scanner which only is testable when driven by a PC. Secondly: why not integrate a shunt into the device? That’d mean you could disconnect the amp-meter without the device going haywire, and wouldn’t require the ugly clip-solution.

On another note: I’d love to be proven wrong, but it seems all electronic projects on Instructables seem to… errm… lack the quality that most electronics sites have.

Posted at 12:05 pm on Dec 17th, 2008 by Sprite_tm

And on a second note: this article could use a title, Caleb :)

Posted at 12:05 pm on Dec 17th, 2008 by Sprite_tm

Hmm, I realize it probably wouldn’t be a big issue, but the exposed wires aren’t shielded. Could easily just use a metal case connected to the ground right?

Posted at 12:09 pm on Dec 17th, 2008 by Peter

sprite: I agree, something like a toggle switch with open/shunt would be a lot easier than the clip (and you could still use an ammeter if necessary).

Also, I don’t care for the instructables format, I find a simple “handmade” page easier to read. But that’s just me.

Posted at 1:02 pm on Dec 17th, 2008 by jproach

@sprite_tm: straight-up wire taps for USB would screw up the impedance of the bus even if nothing were connected and probably cause a lot of failed transactions. Better would be to roll your own differential hi-z probe to build into the cable.

Posted at 1:04 pm on Dec 17th, 2008 by pokey

Hmm if I remember correctly, one of the features of an USB-hub is you can see the current drawn for each port in software.
You can see it in Windows in the device-manager, as one of the tabs in the properties-screen of the USB-hub.

Posted at 1:28 pm on Dec 17th, 2008 by TD-er

I was able to do this with persistance, patience, a multimeter, and just the female USB slot itself.

Posted at 1:55 pm on Dec 17th, 2008 by Link

What? I guess I need to read the instructions before I throw them away next time. What type of hub claims features like this?

Quote

Hmm if I remember correctly, one of the features of an USB-hub is you can see the current drawn for each port in software.
You can see it in Windows in the device-manager, as one of the tabs in the properties-screen of the USB-hub.

Posted at 1:28 pm on Dec 17th, 2008 by TD-er

Posted at 2:37 pm on Dec 17th, 2008 by Trevor

“can see the current drawn for each port in software.”
The Power tab under USB Root hub properties shows the power required for each device. I’m no expert but i believe this is specified by the device not an actual value. unrecognised devices default to 500mA

Posted at 4:25 pm on Dec 17th, 2008 by pip

I’m confused here. Voltage is sourced, not sunk, so every USB device should be 5v. As for the current the USB spec says that devices must not draw more than 500ma so if you’re trying to plan capacity you can just assume that each device is 500ma.

Posted at 5:16 pm on Dec 17th, 2008 by SuperJdynamite

I made a similar ‘breakout box’ USB cable earlier this year to monitor the power usage of USB drives/CD Roms etc., but I put 3 contacts sticking out the box.

The +5v line (just tapped into), and the ground lines of each end of the cable. That way I can not only measure the current but the voltage at the same time, which is handy since my Metrix MTX3282 multimeter can read+display both simultaneously and also display the watts.

I feel it’s important to read both at the same time because when you increase the power drain on the USB port the voltage drops accordingly.

Posted at 5:20 pm on Dec 17th, 2008 by Haku

Let me ask you this: why would you want to know how much current is being drawn out of your USB device?

The devices that you buy from the store will give a current rating @ 5V. You can safely assume it will never go above the max current rating. For all estimation purposes, you can assume “typical” power consumption at about 70% of the total power.

Posted at 5:48 pm on Dec 17th, 2008 by ngth

I realize that its not pretty or very functional in the grand scheme of things, but it’s just something I slapped together for basically monitoring current draw for a previous project.

I’m working on a prettier/smaller solution.

Posted at 5:53 pm on Dec 17th, 2008 by Vincent (gmgfarrand)

Also….
All devices are not created equal when it comes to current draw.

Sure the USB standard is 5V for VOLTAGE..
For example, my Lenovo USB Slimline DVD burner pulls about 120mah, my GPS when it charges about 340mah, my ZEN MP3 player, 450mah.

When modding USB devices or ports, I need to know what kind of numbers I am working with to avoid a “bad day” ;)

Posted at 5:56 pm on Dec 17th, 2008 by Vincent (gmgfarrand)

Not to nitpick, but mAh != mA

mA = milliampere, a measurement of current (coulombs/second)

mAh = milliampere hour, a measurement of charge (coulombs/second * hour = coulombs)

I’m actually surprised that your dvd burner only pulls 120 mA, a cheap optical mouse I just got pulls 100 mA (manufacturer) and it doesn’t use a laser diode.

Posted at 7:12 pm on Dec 17th, 2008 by Peter

@ngth If everything you intend to plug into your USB ports came from the store then you’re on the wrong site.

Posted at 9:21 pm on Dec 17th, 2008 by Steve

Yeah — I think you must mean 1.2a, not 120ma :)… it would take 120ma just to power up the laser on the DVD drive. I’ve seen DVD drives sometimes use a split USB cable that allows you to use two USB connectors to get within the power spec of the port.

Posted at 12:15 am on Dec 18th, 2008 by hex4def6

“On another note: I’d love to be proven wrong, but it seems all electronic projects on Instructables seem to… errm… lack the quality that most electronics sites have.”

I have to totally agree.

It’s okay and nice if someone hacks this together at home. But it’s not sophisticated, anyone who has ever done current or voltage measurement can do it by himself, without instructables.

Posted at 12:47 am on Dec 18th, 2008 by JohnZero

hex,
No, I mean 120ma.. I thought it was weird as well, which lead me to test it in the first place.

The burner actually has 2 USB ports on the back and a DC jack.

One port is just for USB power, and the other is for DATA.

Really annoying….

Posted at 6:10 am on Dec 18th, 2008 by Vincent (gmgfarrand)

“It’s okay and nice if someone hacks this together at home. But it’s not sophisticated, anyone who has ever done current or voltage measurement can do it by himself, without instructables.”

I agree as well, but sometimes, in order to come up with something more sophisticated, you need to start simple.

With the Instructables I have seen/done, when the complication level goes up, the people on the lower end of the skill spectrum bombard me with sometimes “moronic” questions, or just don’t “get it”

For the sake of those, and some of the “slower” techs I work with, I keep me better/more complicated projects to myself or to the places/people that have more skill.

Posted at 6:25 am on Dec 18th, 2008 by Vincent (gmgfarrand)

If you want to make this prettier you can build it into a Digital Multi-Meter yourself.

Cost: $3 DMM from Harbor Freight, $1 USB extension from Dollar Tree.

Matter of fact you can use two DMM and get the voltage of the connection while you are building a meter.

Posted at 8:03 am on Dec 18th, 2008 by nubie

nubie,
Nice thinking….. might have to try that..

Posted at 8:05 am on Dec 18th, 2008 by Vincent (gmgfarrand)

Thanks, it still amazes me that Harbor freight can move these Digital Multi Meters for $3, every time I visit.

I totally get that Instructables is on the simple end of the spectrum sometimes and I think it is great.

Posted at 8:03 pm on Dec 18th, 2008 by nubie

120 ma is the average current draw for the burner. laser applications (I believe) are typically pulsed current, which could be on the order of amps, but, with a low duty cycle, the average current measured on the input to the laser power supply (i.e. from the usb) is much less. for example, 1.2 a with 10% duty cycle would be only 120 ma on the input side. a cap provides this pulsed current which the input supply (usb) doesn’t see.

Posted at 10:40 am on Dec 27th, 2008 by carlton

I’ve never bothered to check the accuracy, but if you go into the windows device manager and check your USB root hubs, it tells you what devices are connected, and what the draw…or maybe just what they’re SUPPOSED to draw… Since it says ‘Power Required’

Posted at 1:52 pm on Jan 3rd, 2009 by TheBakachan

I think a DVD burner requires a wall wart power supply for power. The 120ma may just power logic in the interface.

Posted at 12:31 pm on Jan 5th, 2009 by dcsledhead