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Support Forum » USB drawing too much power

August 28, 2010
by wearetherowboats
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I was trying to make the temperature monitor, everything was going fine until I got to the programming part. The first problem is entirely borne of my own ignorance. It's this bit:

"Mac users need to check /dev for a device like /dev/cu.PL2303-0000211A Using the terminal, list the files in the /dev folder, you should see a file like cu.PL2303-0000211A the last 4 numbers will change depending on which port you plug it into."

I have no idea how exactly to check /dev for devices. I have no programming experience and this is all pretty foreign to me.

The second problem is when I plug in the USB it says it's drawing too much power and that it's disabled the port. When I plug out the USB it feels pretty hot, but I can't find anywhere on the board that I may have caused a short, everything's according to the PDF instructions.


August 29, 2010
by Rick_S
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A good overhead photo of your setup could help us immensly in helping you troubleshoot. If the USB adapter got hot, that is indicative of a short. Does it get hot if you plug it in without the wires connected to the Nerdkit board? (make sure the wires do not touch each other when doing this).


August 29, 2010
by Ralphxyz
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Warning lengthly post, sorry.

The greatest thing about the current wave of operating systems (Windows 7 and OS X Snow Leopard) is that you no longer need to know where anything is any longer to get things done. The built-in search engines, Spotlight for the Mac, are so fast just type in a inquiry and you will have your answer all most instantly. It is now a whole different way of using a computer that new users no longer have to follow the, at times arduous, "Path" to get anything done. Word of warning on the Mac never remove the .DS_Store file from any directories, that is the index file that Spotlight uses to find things. It really is a brand new game allowing a entirely new mind set about using a computer.

/dev is one of the root folders in OS X that is hidden from a regular user such as yourself.

You use Terminal to check /dev. You will literally use Terminal for everything you do between your Mac and Nerdkit so you will become very familiar, and comfortable using it.

So in Spotlight (the magnifying glass in the top right corner of your desktop) type Terminal. The "Top Hit" will be just click it and Terminal will open for you. From Terminal the whole command line world of computing is opened to/for you. This is how every thing was done before the GUI (Graphical User Interface) was introduced on the early Mac's and Windows. You type in a command and hit enter/return and the computer executes your command.

Some people consider this the natural way of interfacing with a computer.

Remove your USB cable from your Mac.

Then in Terminal enter:

ls /dev/cu*

You will get something like this:

/dev/cu.Bluetooth-Modem /dev/cu.Bluetooth-PDA-Sync

Now plug the USB cable back in. Hit the up arrow on your keyboard or re-enter ls /dev/cu* and you will get something like this:

/dev/cu.Bluetooth-Modem /dev/cu.PL2303-0000101D


/dev/cu.PL2303-0000101D is my Nerdkit USB connection.

You can also type cd /dev (cd = change directory) and then ls to see everything in /dev. If you scroll up you will eventually find your USB port.

Different USB ports will give you different port ID's.

Lesson learned "The USB cable has to be plugged into your computer in order to show up". Now that might be obvious to you, but I got caught with that and spent frustrating time trying to figure out why it didn't work (obviously the Nerdkit's User Guide was wrong).

This is plugging the USB cable directly into the Mac if you use a USB Hub it may or may not work so it is best to use the USB port on the Mac itself.

As I said you will be living in Terminal to upload programs to the Nerdkit and to see output from your Nerdkit so lets make a easy way of bringing up Terminal, not that using spotlight isn't easy but try this.

In Finder, Terminal is at Applications/Utilities/ Now this is what I have done I am also new to OS X so there probable are better ways but this works. In finder right click and select Make Alias now left click and hold and drag to your Desktop (you can rename the icon if desired). Now just double click the Terminal icon and you will have your Terminal. Also you can click and hold and drag it over to the dock and you can insert the icon there to be clicked.

There are hundreds if not thousands of things you can/could do in Terminal, for starters look at these Unix Commands. You will not necessarily ever need to use these commands but if you want to know the real basics of computing it is good to start here. The GUI uses these commands but covers them up (abstracts them) from the user.

One other command you will use is Screen.

Screen is used to see output from the NerdKit on your computer screen.

Again in Terminal:

On the Menu bar under Shell --> New Window click Basic or one of the other screen choices.

You will have a new Terminal window:

Type in screen /dev/cu.PL2303-0000101D 115200 adjust for your USB port of course.

You will see output from your Nerdkit if your program is so programmed (most Nerdkit projects have pc output).

To stop (kill) the Screen type Control-a Control- (Ctrl-a Ctrl-).

Another command that you will find helpful if you want to learn Unix (the under lying operating system of OS X) is man.

In Terminal type man screen.

You can see the manual for any Unix command (not that you would want to of course).

So this should get you started, sorry about the length but it seems necessary and will be good for other new users using a Mac to connect to their Nerdkit.

Welcome to the group and enjoy.


August 29, 2010
by Ralphxyz
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That is Control-a Control-\ (Ctrl-a Ctrl-\) to kill Screen.

Darn that is the second time the forum software did that to me, the secret is to use two \\ to get the single \, each one has to be escaped.

And I thought it was me.


August 29, 2010
by wearetherowboats
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Rick - I'd obviously stupidly shorted something somewhere, so I rebuilt and problem was solved. Thanks though. Still can't figure out what the original mistake was, but there must have been one.

Ralph - Thank you so much for your help. It got me one step further along, but now I'm completely stumped again. Stuck entirely at step 10c. I haven't a clue how to get Terminal to program the chip. I've tried doing it a couple of ways, no joy. I realise that these questions are so ignorantly basic that I may as well be asking how to turn my computer on, but I really appreciate the help.

Guys at Nerdkits - your PDF may need a little dumbing down for cretinous customers like myself.

August 29, 2010
by wearetherowboats
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Addendum - worked it out. Didn't realise that I had to change directory to the initialload folder and then just type "make". I was trying things like "make initialload" and "make Makefile".

Phew, this learning lark is hard!

August 29, 2010
by Ralphxyz
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Been there done that.


March 16, 2011
by plinko
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wearethewrowboats: I had a similar problem of the USB drawing too much power. I did the same thing as you and rebuilt and the problem was solved. Here's where I think the problem was, and might help another reader: I had introduced a switch to power on/off the board. Instead of putting power into the red rail, I put it into one side of the switch. I put the middle of the switch to the red rail and then grounded the other side of the switch. This created a closed circuit (no resistance!) when the power was 'Off' and the laptop didn't know what to do with all that freedom. It's like sticking a fork in a light socket, linking + to - like that. Oops.

I'm finding working with circuitry to be about making sure I'm not setting anything up poorly -- as opposed to making sure I'm setting things up right. Like... practicing shooting a basketball by concentrating only on not throwing it outside of the hoop. Hurts the brain.

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