well technically you are not supposed to pull more than 0.5A (500mA) from a USB port. If you have a self powered hub, and it isnât smart enough to monitor load current on each hub port, you may get it to deliver 2A. The contacts on a USB connector are probably good for 1-3A depending on the connector. Most servos will run down to mid 4V range well enough but you also have to remember the power (torque/speed) of the servos is going to drop with supply voltage.
Why not just buy 2 or 3 battery packs and a quick charger, like for RC cars? It may be cheaper than a bench supply capable of running a full biped without servo stalls.
Why not? There are many things you can buy that are powered by USB. I seen a USB cup warmer, USB clock, USB fish tank (fake fish), USB you-name-it! They are all powered by USB.
well if your gona just run programs on the atom bot board, I guess there is no harm. If you plan to run 20 servos from this source, the servos will cause a nice load and who knows what might happen.
And they all draw under 500ma (0.5A) OR have their own external power supply.
So if you power the servos from somewhere else you can probably power the micro part from the 5V, but do not try to power the servos from the USB or you risk smelling the special smoke.
Well, thereâs always the DIY approach to making a power supply.
Going from memory, whatâs needed is a transformer (two inductors, a.k.a. âcoilsâ, wrapped around an iron ring) to step down the voltage.
Then a fullbridge rectifier (thatâs just four diodes aranged nicely) to modify the AC sin wave into a positive âbouncingâ current.
And then a bunch of filter caps (and an inductor?) to smooth out the âbounceâ into a proper DC current.
Anyone done this before?
I think I found this in a Digital Electronics book that I got from the library.
When I go back, next, Iâll see if I can get it again, so I can post a schematic.
Now youâre talking about commercial devices! Before you were talking about soldering wires onto a DB9, which is directly powering something from the PCâs internal power supply! The USB port may be fused, or some other protection may be in place.
Actually Jim, I was talking about both. DB9 and USB. I mentioned that USB has a 5v power thingy in one of its pins and thought that might be useable for a powersupply while your developing with the ABB or SSC-32⊠I also asked if it would be possible to somehow get 6v to the DB9 from the computerâs internal power supply.
The USB port can probably power the boards, but not any attached motors. Most computer power supplys supply +5v and +12v. The +12v supply is usually weak compared to the +5v part. You can use a +5v regulator and a diode or LED on the regulator ground to get colse to +6v when connected to the +12 supply. I wouldnât try powering any motors from the computer power supply. External power supplys are fairly inexpensive.
I canât help anyone out with specific part numbers, since I havenât built this circuit myself, nor plan to.
I donât like playing with household AC, when I can help it.
Looking at this, though, Iâm wondering if youâd even save money buying the parts and making it yourself, since a regulated 5V wallwart is only about 15 bucks.
::points down at red disclaimer::
I will not be held liable, nor pay your medical bills, or even rush over to the hospital to pat your hand and mutter simpathies when you electricute your self.
Be warned.
Uh, well you have an idea what it feels like anyway.
Nick, do you want to tak about this circuit or are you just fulfilling a mission to post it? It graphically potrays the concept at an acceptable level but it needs some help with the text and values shown. Iâll just leave it at that unless people want to talk more.
