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I have a project which will require using a Raspberry Pi in a low power environment, but it will also require a 3G connection. I have not done any tests, yet, but I am under the assumption (and correct me if I am wrong) that a 3G modem plugged into a Raspberry Pi and connected to a network will use power, and given the environment, any extra power usage is a non requirement. So, how, programmatically, can I turn on and off a 3G modem, or the USB connector on a Raspberry Pi?

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    AFAIK You can't turn off a USB port, so it would rely on the 3G dongle having a power saving mode - it probably uses less power when not connected... but it probably uses a reasonable amount of power to connect/disconnect. – Alex Chamberlain Oct 12 '12 at 14:54
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    thing is, this will be a completely autonomous and remote unit... it should be turning on and off 3G as needed... there wont be anyone there to unplug or plug it in... hence the programmatically part... – TiernanO Oct 12 '12 at 23:11
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    As Alex said, there is no mechanism to control power to the Pi's USB ports from software - they are directly connected to the supply rail with only a passive current limiter. So unless you can tell the peripheral itself to shut down/sleep, you'll need an external power switching device, which you control over USB itself or via a GPIO pin. – Chris Stratton Oct 13 '12 at 15:36
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Sadly there is no way to fully power off with software alone. You will need to add a switching circuit connected over the GPIO pins to trigger a "hardware disconnect" by cutting power to your hardware.

Edit:

To switch with GPIO it's just a simple transistor circuit.

enter image description here

B is attached to your GPIO pin. Depending if it's HIGH or LOW the transistor is on or off. C and E you put the power line to the USB-Device (RL).

For more detailed information better look at this site: http://www.kpsec.freeuk.com/trancirc.htm#switching and specially at http://www.kpsec.freeuk.com/trancirc.htm#ic

  • Think you could go into more detail about how to do this? – Jivings Oct 25 '12 at 7:46
  • Sure. I'll edit – Mose Oct 25 '12 at 7:54
  • yea that is good- you can put that transistor in a short USB extension cable.You will need to cut it open and intercept the power lines talked here. Then you can plug 3G into the extension and control power. I like it +1 – Piotr Kula Oct 25 '12 at 11:12
  • That looks promising! Thanks! will have to have a chat with my Electrical Engineering friend to help with that, but fingers crossed! Thanks again! – TiernanO Oct 25 '12 at 12:11
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I would not advise you to turn an USB device ON/OFF just by using a transistor base switch because proper power ON/OFF protocol and electrical interface should be used as defined by the USB specifications.

I would rather use a switchable USB hub that allows you to turn ON/OFF any of it's downstream ports through software by using a simple command.

Something like this USB switchable hub should work for what you want.

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    That looks Sooo cool! I have to try that... I'm thinking this could also be handy for smart charging of phones... Hmmm.... Thanks! – TiernanO Nov 7 '14 at 23:25
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    Disclaimer: I now working at Yepkit. So you may consider me biased on this subject. – electrfunch Nov 11 '14 at 18:24
  • As a device can be plugged by a user at anytime, USB specs state that this must be handled by drivers and devices. So I don't see the point of spending 29€ when you can build simple electronics for cents with the same result and also backed by specs. – Mose Feb 21 '16 at 14:13
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You can use my tool uhubctl, it supports Raspberry Pi model B+, 2B or 3B - these models have hardware ability to turn USB power off and on. But keep in mind that this hardware only supports turning off or on all USB ports at once, not independently. However, USB and Wifi+Ethernet power rails can be controlled independently.

Use it like this:

Turn off power to all USB ports (must use port 2):

uhubctl -p 2 -a 0

Turn on power to all USB ports (must use port 2):

uhubctl -p 2 -a 1

Turn off power to Wifi+Ethernet (must use port 1):

uhubctl -p 1 -a 0

If your Raspberry Pi does not support USB power switching, you can connect external USB hub that does (see list of compatible models), and control power on that external hub using uhubctl.

2

Hi I agree with @electrfunch since I am working on a Project of controlling devices on the USB ports. Instead of on-board Electronic Circuit proposed by @Mose, I created my own Isolation Board using Relays and looks similar to the USB Switch Hub and this makes sense since even though initially ignored- Currents within the Raspberry Pi will start becoming a criterion on a longer run which might affect your Pi performance.

For what I mean, you could refer these manuals for Low Current measurements:

Reference 1

Reference 2

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