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Silly problem with power over USB

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#1 Wernfried


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Posted 27 October 2014 - 05:15 PM

I bought a W-LAN router (TP-Link TL-WR710n) since it has an USB port. I assumed I can use it as WLAN and power supply as well.


After I configured the WLAN router  to be able to get Access to the Internet with my Netduino 2 Plus, I was happy and started to coding a bit further. All works well, when I connected with USB to my Laptop and the Ethernet-Link to the router. My application sends a mail message to my account when the application starts.


Thenafter I connected the USB to the router and have been supprised not getting the mail message. At the first glance Netduino seemed to work, the LEDs on board are on and the Ethernet-LED is blinking some times.


To more dive into the reason I added some code to the start of my programm to switch the Onboard LED on and off and on. This works great when USB is linked with the laptop. But it doesn't work, when I put the USB-cable to the router. The router specification says USB has 5V, 100mA. Is this too less for Netduino working? It is sufficiant to power my Smartphone.


Anyone any ideas?

#2 Paul Newton

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Posted 28 October 2014 - 12:32 PM

Hi Wernfried,


I think your USB port will not be able to supply enough current to drive the Netduino Plus 2 when active. The difference between the Netduino and a phone is that the phone has a battery that will smooth out the demand on the supply - e.g when the phone needs a higher current, the battery will supply it - the rest of the time the battery charges.


I was going to refer you to the Wiki page that has a comparison of Netduino boards, but the power supply figures for the Plus 2 are not in the table. However, looking at the Plus v1 in the table, it is listed as taking 80mA when active. The Plus 2 will be similar, so it is a safe bet that when your program turns on an LED, it could easily be taking the current consumption too high for the supply you have.


It might be better to take the power from the same supply that the router uses. Assuming the power goes into the router through a barrel connector, you could make a simple splitter using a plug and a pair of sockets, and pass the power to the barrel connector on the Netduino.


Hope this helps - Paul

#3 Wernfried


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Posted 31 May 2015 - 04:55 PM

I will reopen this thread.


I beleaved, the given answer was correct, that my TP-Link router will not provide enough power to run the N2P.


Yesterday I've got a Raspberry PI 2 and I've been installing Windows 10 IoT on it and could get it to run. Then I prepared the PI2 to work with the TP-Link router. Then I've powerd it up with the USB of the router trying if it can support the PI2 and suprisingly it did.


 I thought the PI2 needs much more power then the NP2. Spec says that the PI2 consumes 420mA in idle state, which is 5 times of hat N2P.


Can someone explain me, where my fault is or if the N2P has a problem.

#4 Chris Walker

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Posted 01 June 2015 - 05:17 PM

Hi Wernfried,

The router specification says USB has 5V, 100mA

As Paul wisely noted, the port on your router is not a standard-power (~5V, 500mA) USB port. It only provides 100mA and is designed for lower-power USB devices and self-powered (i.e. battery- or wall-adapter-powered) USB devices.

Netduino does require quite a bit less current than x86 mainboards, but you'll still want to power it off of a standard-power USB port since its current requirements may go above 100mA.

This also applies to USB hubs... If you plug a bus-powered USB hub (i.e. no external power adapter) into your computer it will typically take the 500mA of power it received and allocate only 100mA to each port. This is fine for keyboards--but you need a powered USB hub (which provides 500mA to each USB port) for Netduino and other more powerful devices/devboards.


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