# USB hubs & cables for 16 arduinos running in a PC

Hello, I know it is a stupid question but I have to ask you guys before I spend money.

I have a project with 16 arduino boards eventually connected to one usb port of a PC. (The other usb ports will be used for other devices.) These arduinos are going to be arranged in a circle (with a radius of 10 feet) and those 16 arduinos are connected to total 4 usb 4-port hubs at the center of the circle, and the 4 hubs are also connected to a main 4-ports usb hub located at the same center spot with the other hubs, and then the main hub finally needs to be hooked up to a PC which is 30 feet far from the center circle. I know it's little bit complicated but they needed to be like that.

So now, I have to purchase 16 usb cables (10-15 feet long each), 4 usb hubs (4 ports each), an extra usb 4-ports hub (as a main hub for the other 4 hubs), and a 30 feet long usb cable as well as an active repeater (for the 30 feet cable) maybe??.

My question is... do I have to buy all 5 self-powered hubs or 1 self-powered hub and 4 bus-powered hub, or doesn't it matter? I know that a usb cable has a length limit to approx. 15 feet, so do I have to buy something like an active repeater for the 30 feet main usb cable connected to the pc?

I am trying to find a cheapest way to solve the problem but don't know exactly what to buy yet.

Could anyone help or even some advice for me? :-)

Thanks, bsjeon

hi

let's say 16 boards will consume 75 milliamps each (sort of the bare minimum...).

That's 16 X 75 = 1200 milliamps, or 1.2A. That's with nothing connected.

Also, each hub will consume current internally, say 5 X 50 ma = 250ma.

So you're up to 1.45 amps and you haven't connected anything the the Arudinos yet. Sounds like self-powered hubs are the way to go! You might get by with the first hub from the computer being self-powered. You'll find out soon enough, because part of the USB specification requires overcurrent protection, so they all have something called a PPTC "fuse" inside. These blow and then reset, but they never reset back completely... you wouldn't want to overtax them too often.

hope this helps

D

PS: if you want to save money then buy one 9V (2 or 3 A) regulated power supply and just string the DC power out to the Arduinos.

First, thank you, Daniel for your advice. Let me verify what you said.

I currently have one self-powered 4-port usb hub (2.0 amps) and one low-cost bus-powered 4-port hub.

I think I can use the self-powered hub with 2amps as a main hub, right? For the other 4 hubs, it sounds I can use 4 cheap bus-powered 4-port hubs since the main hub takes care of the required amps, am I right? Or just to be safe, do I have to use 4 self-powered hubs instead? In my case, all electronic devices attached to each arduino boards use different power sources so I think those 16 arduinos use only the minium current I guess.

For the connection between the PC and the main hub (self-powered/2amps) through the "30 feet-long usb cable", what do I have to do? Do I buy a regular usb cable or do I have to buy a USB active extension cable or something like that since it is longer than the limit length, 15 feet?

Could you recommend some reasonable products (hubs and active extension cables) with relatively low costs?

Again, thanks for your help. :-)

-bsjeon

I have tried a usb extender http://www.lindy.com/uk/productfolder/04/42805/index.php

with usb devices and found it very problematic - worked sometimes, not others with exactly the same setup (ie just turn the machine off and back on with out changing anything and it would not work) had to rethink project in the end as it was not reliable at all.

We used midi in the end for the long connection, but you could try a long serial run like that.

Another option would be zigbee modules (the new board is available) which would get rid of all the wiring, you would just need to get power to them.

Hi bsjeon

For the connection between the PC and the main hub (self-powered/2amps) through the "30 feet-long usb cable", what do I have to do? Do I buy a regular usb cable or do I have to buy a USB active extension cable or something like that since it is longer than the limit length, 15 feet? -bsjeon

I'm afraid you will definitly run into trouble, if your cable is longer than 5 meters (from the USB-specs) I guess the cheapest solution would be yet another cheap (Bus-Powered-) Hub that simply acts as a repeater.

Eberhard