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Thread: HOWTO: Power a USB Hub for the G4

  1. #1
    Raw Wave god_of_cpu's Avatar
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    HOWTO: Power a USB Hub for the G4

    The Problem
    Depending on the number and type of devices you want to connect to the G4 you may need to use a USB and hub and if one or more of the devices consume a fair bit of power (i.e. external sound card, external hard drive), you may need to provide a power to the USB hub for it to work properly. If you don't power your USB hub, your devices may act strange when connected to it. They may not work at all, or they may appear to work, but cause errors or have erratic behavior.

    Powering a hub in the car is actually a trivial problem with a non-trivial answer. Unfortunatly, you can not simply hook up a the unregulated 12 volts readily available in the car directly to the hub. USB hubs require regulated 5 volts and what is more, they should be powered whenever the computer is on. This is actually different from when the car is on. Since the computer must go through a shutdown sequence when it goes to hibernate or standby and this sequence is initiated by turning the key off in the car and doesn't end until a number of seconds after the car has lost power, you can not simply provide power when the accessory power of the car is on. If you do, your hub will lose power before the computer shuts down and windows will detect the forceful removal of the devices and it will wreak absolute havok on the device drivers. This will result in bad things happening the next time the computer is started.

    The Solution
    Simply put, the solution is to provide power to the USB hub always and only when power on the USB bus from the computer is on. This can be implemented with a 5volt SPST relay that is triggered by the USB bus and turns on a 5 volt Point of Load (POL) power supply that in turn provides power to the USB hub. This may sound complicated, but really its pretty easy to do, you just have to make sure you connect the wires to the right places.

    Parts Needed:


    Tools Needed:
    • Wire Strippers
    • Soldering Iron and Solder
    • Heat Shrink Tubing
    • Wire 18 gauge or higher



    Before you begin, you should first familiarise yourself with the Carnetix POL power supply manual, particularly section 2.2.2 on use as a Stand-Alone POL regulator.

    First we shall make the trigger for the 5 volt relay. To do this, cut the USB extention cable completely in half at the center. You will notice there are 4 wires inside and the wire is surrounded by shielding wire. Strip both ends of the cut cable about 2 inches or so being carful to leave the metal shielding wire intact. Then strip the ends each of the 4 small individual wires on each wire.

    Now get 2 6 inch lengths of wire and strip both ends of them. Twist one wire and the two red ends of the usb cable back together and the other wire and the two black ends (negative) of the usb cable back together. Twist the grend ends together then the white ends back together of the usb cable. These are the data lines and are not used. They were just cut to make striping the wire easier. Also twist the wire shielding from both ends of the cable back together. Use solder on all 5 wire twists, place and heat the heat shrink tubing over all of them.

    The relay should have 2 poles on one side and 3 on the other, place the heat shrink tubing over solder the two loose wires coming from the USB cable you just made.

    On the side of the relay with the 3 poles, you should connect the cars unregulated 12 volts to the input pole, usually the stand alone one and the other to the pole that is active only when the 5 volt trigger voltage is applied should be soldered to the green wire from the POL power supply.

    Finally hook up the rest of the wires on the point of load power supply. Providing the cars unregulated 12 volts and ground where indicated in the manual and hook the red and black output wires to the positive pole and negative outside of the USB hub.
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  2. #2
    Variable Bitrate
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    Question couldn't I use the blue amp turn on wire to trigger the realy on instead of loosing one of my usb connections off of the g4 ?

  3. #3
    Raw Wave god_of_cpu's Avatar
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    Quote Originally Posted by lagunatl2k View Post
    Question couldn't I use the blue amp turn on wire to trigger the realy on instead of loosing one of my usb connections off of the g4 ?
    Unfortunatly no, the amp line is actually turned on after the system is started and before it completely shuts down.

    The only extenal wire that turns on and off when USB is suppose to turn on and off is the USB ports coming from the G4.
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  4. #4
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    nice howto! very helpful!

    i suppose it is the same procedure powering up a usb hub at every PC not only at g4, right?

    what if i need more usb ports than a 4-port usb hub can provide? sth like 8-ports (one 8-port usb hub OR two 4-port usb hubs) let's say..

    do i need one more carnetix attached the same way as the first in a different mobo usb port for thw two 4-port usb hubs solution?
    if i use the 8-port solution does carnetix provide enough power to the 8-port hub? (500mA x 8 = 4A, i think carnetix provide just 3A max, right?..)

  5. #5
    Raw Wave god_of_cpu's Avatar
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    Quote Originally Posted by Nazx View Post
    nice howto! very helpful!

    i suppose it is the same procedure powering up a usb hub at every PC not only at g4, right?

    what if i need more usb ports than a 4-port usb hub can provide? sth like 8-ports (one 8-port usb hub OR two 4-port usb hubs) let's say..

    do i need one more carnetix attached the same way as the first in a different mobo usb port for thw two 4-port usb hubs solution?
    if i use the 8-port solution does carnetix provide enough power to the 8-port hub? (500mA x 8 = 4A, i think carnetix provide just 3A max, right?..)
    Yes, it should work for other systems, but there are easier ways if you access to the power supply and extra power, just power the hub directly from the 5 volt rail of the power supply and your done. You can't access this on the G4, so you need an external power supply.

    The carnetix has a max of 4 amps which means if you hook up 8 devices that draw the max of .5 amps for each usb device, you will need a bigger power supply. If you have alot of devices that don't draw that much power, your not going to max out the 3 amps. Better yet, you should just add 2 4 port hubs, power 1 for your high power USB devices and use the other for the lower power devices that can just use bus power and you won't have to worry if your overloading the power supply.
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  6. #6
    Low Bitrate drakino's Avatar
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    On a related USB note, I'm going to pick up one of these for adding USB ports to the G4. Looks pretty slick, should allow for some good custom installs with USB ports hidden away, and this has been the only "squid" hub I've seen with extra power. Just need to feed it down the 5v line of the red USB connector.

    http://www.radioshack.com/sm-gigawar...i-2498117.html

    Not in stock online, but shows in stock at most of the stores near me. Will report more on how it works later.

  7. #7
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    May be slightly off-topic here, but nevertheless: if you are running short of available USB ports, you might consider one of those combo wifi/bluetooth adapters. Have no idea of how good they really are, probably worth experimenting.

  8. #8
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    Quote Originally Posted by god_of_cpu View Post
    Yes, it should work for other systems, but there are easier ways if you access to the power supply and extra power, just power the hub directly from the 5 volt rail of the power supply and your done. You can't access this on the G4, so you need an external power supply.

    The carnetix has a max of 4 amps which means if you hook up 8 devices that draw the max of .5 amps for each usb device, you will need a bigger power supply. If you have alot of devices that don't draw that much power, your not going to max out the 3 amps. Better yet, you should just add 2 4 port hubs, power 1 for your high power USB devices and use the other for the lower power devices that can just use bus power and you won't have to worry if your overloading the power supply.
    thanks for the tips!

    i didn't know that g4 is so inaccesible..!

    i know that in an ordinary pc i can use the PSU's 5v rail to power up the usb hub, but i don't want to drain more power from the PC's PSU and push it to the limits. besides in this case i can also use the hosts usb hub (mobos usb hub) without adding any external usb hub! i just don't want to drain PSU's power..

    anyway, i haven't thought using the two 4-port usb hubs solution, using one for the high power USB devices and the other for the low power USB devices that can just use bus power, therefore i'll consider that as a very good option!

    in any case i will need a bigger power supply than the 3A carnetix powering let's say an 8port usb hub, do you have any suggestions? Sorry for the off topic!

    Many thanks!
    Nazx
    TK

  9. #9
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    Is there a reason why you can't eliminate the relay and wire the GRN/BLK wire of the CNX-P5V directly to the USB power from the G4? Also, wouldn't it be a good idea to fuse the 5v output prior to the device or hub?

  10. #10
    pim
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    Can anyone recommend a relay that I can order from Conrad?

    I see a lot of Omron relays there, but not the one linked to in the original article.

    Thanks,
    Pim

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