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Topic: Using a USB only for VCC (Read 923 times) previous topic - next topic

erg144

I've been looking through the arduino schematics and I'm not sure I really understand the USB connectors.  If using USB only power, it seems the power does not go through any regulator.  Does a USB provide stable enough power to do that?  I was thinking of eliminating my barrel jack and 9 volt input and simply use a USB charger and a few filtering capacitors,  but not sure how well this would work.

In my case, I need a USB connected to a computer for setup of the micro.  Once setup, I would like to just use the USB charger for the power plugged into a wall wart (reduce the cost and size of my board).

This seems like a good idea, but if it is a good idea, why are so many boards designed like the arduin?   

 

James C4S

USB is a regulated voltage.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

erg144

is that true even is using a usb cable and a wall wart usb charger? 

majenko

Quote
is that true even is using a usb cable and a wall wart usb charger?

If it is a USB charger, and not just any old wall-wart that you have soldered a USB cable to, then yes.

It's all in the USB specs.

James C4S


is that true even is using a usb cable and a wall wart usb charger? 

If it has a USB logo, then most likely.  Keep in kind those USB supplies aren't technically chargers, they are supplies.  The charging circuit is usually built into the actual device.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

toughsled

I don't believe Arduino boards regulate the voltage coming from the USB socket as there isn't a significant voltage drop from the USB 5V supply to the Arduino 5V supply.  The DC socket is regulated however. 

Claghorn

I didn't trust wall chargers much (especially cheap ones), so I tested a few different USB sources with the results near the top of this web page:

http://home.comcast.net/~tomhorsley/hardware/arduino/teensy.html

The Staples brand USB charger I tried had the most consistent voltage from no load up to about 500mA, but actually I didn't find anything that seemed dangerous (in my very small sample size).
http://home.comcast.net/~tomhorsley/hardware/arduino/arduino.html

James C4S


I don't believe Arduino boards regulate the voltage coming from the USB socket

They don't.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

Docedison

#8
Jun 10, 2012, 01:29 am Last Edit: Jun 10, 2012, 02:28 am by Docedison Reason: 1
USB chargers are made in the same places as wall warts, they are wall warts. Buy a New one with a 9V switcher in it and buy a spare, they are inexpensive. There are also "Premium" devices available . High Reliability type Battery Chargers  The reliability for Chargers/Wall Warts aside from age or condition is more a function of the Mains Power connected to it. Line transients will destroy either type equally well. One other consideration is that the transformer types draw nearly full load current from the line, unloaded and Disconnected from the device and plugged in to the wall.The newer switcher types do not.
For most if not all the circuitry is the same for USB or 9V PSU's as there are only so many different "Off Line Switcher devices" 3 or 4 by my last count. New devices of both types are equally likely to fail from the device inside that controls the 110V in and supplies the power. The main difference is a resistor value or a different control part and the connector/s & case. If you wanted to use it on a boat or in a car there are inverters to use from automobile power connectors (cigarette lighter sockets).
What is the issue with using the regular 7 - 12V input connector, are you going to build your own board later?. The DC in connector will always supply regulated 5 Volts and at about 100 mA more than the USB port will and you won't be at the mercy of Staples... What happens if your USB charger goes bad and Staples quits selling that Exact type of charger, Buy another set for a new series of tests to select the "Right" one? It (the USB port wasn't at least in my mind meant as the primary source of power for anything except loading a sketch, IMO). On my setup the only time I connect the USB port is when I need the serial monitor or to load a sketch. If I am learning how to do most anything on my Ono or Mega, I always use an external PSU for the breadboard and the Uno as well because I know that it is tested and stable. In the beginning I have at least the sure knowledge that my power supply at least is OK., Also I have found External DC power supplies generally more reliable than computer USB ports as computers are for a number of reasons a great deal less reliable than wall warts. If you were planning on using a Hub at any time for power you will still need a wall wart to power the hub...  All I can see you doing is to change the type of Wall Wart from one with a single connector to one with not only 2 connectors but also a type which is delicate... step on a USB connector and ruin it... more often than not. Again IMO

Doc
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

Claghorn


What is the issue with using the regular 7 - 12V input connector...


Well, for me the issue is that the device I'm building has a Teensy board in it, and USB is the only (trivial) way to get power to it (plus it can talk to the computer over USB or bluetooth, so if you are talking USB, might as well kill two birds with one stone).
http://home.comcast.net/~tomhorsley/hardware/arduino/arduino.html

Docedison

Quote
I was thinking of eliminating my barrel jack and 9 volt input and simply use a USB charger and a few filtering capacitors,  but not sure how well this would work.

This was the comment that I was addressing... There is a subject that I briefly touched on and that is that there are 2 types of USB Port...
One can supply a max of 100 mA and the other can supply 500 mA. Clearly that might be a further issue for you where the external PSU will not be. Does this explain my concerns better?

Doc
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

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