Need help with USB powering options

[s4per]

The setup: I have an aopen i945gtt-vfa mobo with a T2500 cpu and 1GB of RAM. I have one powered USB hub. It has hooked to it: dvd player (storix USB2.0), OBD-II cable (vag-com), RF keyboard (gyration), Touch screen (Xenarc 700TSV), bluetooth adapter (Targus), and wireless adapter (Dlink WUA-2340) . I have a USB GPS (Bu-353) plugged directly into the mobo's USB port and a non-powered USB hub which usually has nothing plugged into it (have it for occasional thumb drive needs, etc.). Both the hub and DVD player external power is currently being supplied by the second output of the 1900.

The problem: The USB bus stays powered when the PC is in standby which drains my battery.

The current work around: To work around this, I have - in the past - cut open the USB cable, cut the +5v and ground wires, and spliced and soldered these lines (the ones leading back to the device or hub) into the respective wires of the 4-pin Molex connectors coming from the PSU. This way, power is only supplied to the USB devices when the PC is on.

The Questions: I'm building V2 of the carPC, and I'm wondering if I should follow the same approach or a slightly different one. What is the best way to power all of these devices?

1. Should I do it exactly as before? i.e. Take the USB cable for the powered hub and the GPS and splice their +5v and ground lines into the Molex connector?
   
2. Should I use just the secondary output of the 1900? Could that one output handle ALL of the USB devices mentioned above? i.e external power for the usb hub, external power for the dvd player, power for the hub's USB cable, and power for GPS's USB cable?
   
3. Should I get the additional cable for the third output on the 1900 and leave the USB hub power and DVD power on the secondary output, and then splice all of the USB cable power wires onto the third output?
   
4. Is there a better option all together?

Any thoughts or guidance is appreciated.

Thanks,
Per

[MikeB]

I assume you are using standby so you can get a fast resume when you turn the PC back on. In my tests, with no USB devices connected to a Via MII-12000, it still consumes over 1W in standby, or about 100mA from the battery. This is still enough to drain the battery over time. To some extent, the P1900's 'deadman timer' protects you. The 3 day deadman timer would limit the battery drain (at 1W) to 7.2Ah which is probably about 1/4 the capacity of a typical battery in average condition; maybe roughly the same as leaving the headlamps on for 3/4hr - which will kill many an apparently healthy battery. In my opinion 10.6V is too low for the battery fault voltage and I would be surprised if you could reliably start the car with the battery in this state.

If you're happy to live with this, then I think your current solution is probably the best you can do. I think that the 2nd output of the P1900 is rated at 3A so should be fine for a 4 port hub plus one other USB device at full current. I don't know how much current a laptop DVD drive takes.

The P2140 will give you more flexibility (when it's available) as you can set the deadman timer and the low battery shutdown voltage.

I'm not sure how well XP reacts to having the power cut when it's in standby - I'd be interested to hear some experiences. Also, as a matter of interest, what does your AOpen board do with its power outputs when it's in standby?

Mike.

[s4per]

"what does it do with its power outputs" - not sure what you mean here, you mean the power outputs from the PSU? Those are not powered during standby, that's why I use those to tap into. Not sure what else you may be referencing?

I know standby will kill my battery if i don't start and drive the car at least every 2 days. I'm all right with this; I've been in hibernate mode for the last 2-3 years and am looking forward to a more instant experience.

I'm still interested to hear which one of my options would be best. Mikeh?

[mikeh]

I would suggest running all of your USB components off of either the secondary output, or a combination of the P1900 secondary and a P5V. If you feel that the total current of your USB devices will exceed 3 amps (unlikely) you could get the P5V and split your USB load between the P5V and the secondary output of the P1900.

How are you powering your touchscreen? Are you sure it's not consuming current when you go into standby (causing your battery to discharge)? If I leave my Lilliput powered and remove the video signal (which makes it appear to be OFF), the screen continues to consume 250mA. Most people jumper their P1900 secondary for +12V and power their USB devices off of a P5V.

Also, I'm not sure why you are not jumpering your secondary output to "follow ignition". This way, your secondary output turns OFF when your ignition is OFF. If you jumper your secondary output to "follow the primary" output, your secondary output will never turn off (since the primary output stays ON in standby). Did I miss something?

[s4per]

Thanks for the response, Mike. Very good point about the touchscreen. That may very well be an issue as I do have it in standby mode when the PC is powered down / in standby. Within two weeks I'll have a different HU with screen (http://www.digitalww.com/DWW-6500.htm) and I'll make sure this standby drain is not present then (I think that will be the case out of the box).

I am using 'follow the ignition' for the secondary output which is connected to one USB hub and the external power for a DVD drive that's also connected to that hub. The problem though is even when this powers off, the USB hub and the devices connected to it still draw power through the +5v line that runs in the USB cable itself. That's why I need to doctor the USB cable to get the same 'follow the ignition' effect.

Given that, for each externally powered USB device, I have to think about TWO power sources: one for the external power, and the other for the +5v line in the USB cable leading to that device. This is what has pushed me towards utilizing the Molex connectors.

I did an experiment last night: took 2 USB extension cables, cut the +5v and ground lines on each, and connected each to the same Molex connector. Attached to the extension cables was one 7 port hub and one GPS mouse. Connected to the hub was: touch screen, OBD-II connector, RF keyboard, DVD player, and a bluetooth dongle. The results were that when I fired up the OBD-II software, I would get 'USB not recognized' errors, something which I've associated with devices not getting enough power based on prior results. All of these devices work just fine if I plug them into the USB ports as someone would normally do (i.e. no doctoring of cables). I do not have a complete inventory of how many amps each device draws...I know I need to do this.

Still, what the results of the experiment say to me is that I'm apparently drawing more than 3 amps from the GPS mouse and the USB hub combined, since the Molex based connection is apparently not giving it enough power and it's good for 3 amps IIRC.

What I'm thinking now is:

1. USB hub external power and external DVD power will be powered off of P5V
2. Screen will be powered off of PSU secondary output
3. I want to use the power from the USB ports...Here's my thoughts: cut the USB extension cables as before, but instead of connecting one end (the end leading to the peripheral) to a molex connector and leaving the other end cut, I put a relay in between the wires that gets triggered off of a Molex connection. Something like a DPST would seem to do this for 2 USB cables at a time. This would just use the power supplied to the Molex to trigger, and once turned on, the actual power being supplied to the USB devices would come from the USB ports themselves, right?

I'd really love some confirmation of #3 above. Will it work as I think it will? i.e. the power will come from the onboard USB port only and the molex would only be used to activate the relay not to supply power to all of the devices? If it works like this, I think it would solve my issues. If it works like this: what type of relay would I need (amp / voltage spec.)?

Thanks for your insight,
Per

[MikeB]

Your (3) should work. Most relays will be OK for this; the USB voltage is 5V at 500mA max.

However, I don't understand you are having problems with

"I did an experiment last night: took 2 USB extension cables, cut the +5v and ground lines on each, and connected each to the same Molex connector. Attached to the extension cables was one 7 port hub and one GPS mouse. Connected to the hub was: touch screen, OBD-II connector, RF keyboard, DVD player, and a bluetooth dongle. The results were that when I fired up the OBD-II software, I would get 'USB not recognized' errors, something which I've associated with devices not getting enough power based on prior results."

I think it may be better not to cut the ground, just the 5V as there should be a common ground in your system anyway and it's possible you're injecting some noise. On the other hand, in my experience USB is quite resilient to noise issues. One thought: are you sure your USB extension lead was rated for USB at 12Mbps? I have had similar problems using a USB lead hacked from another product to make an extension Apparently some of the cables used on mice and keyboards are 1.2Mbps USB only. If you try to hack one for use in a USB 1.1 (12Mbps) application it doesn't work reliably.

I would be very surprised if that list of USB devices consumed as much as 3A, but you could remove, say, the BT dongle or the DVD and see if the rest then work reliably.

Mike B.

[mikeh]

I really doubt that you are drawing > 3 amps from the +5V output. One way to tell for sure is to measure the +5V line with a voltmeter and see if it is still regualting to +5V. If you are overdrawing the regulator, the voltage will drop. However, I have regularly loaded this output to much more than 3 amps. If you have adequate air circulation, the secondary output can actually easily handle more than 3 amps.

I would get 'USB not recognized' errors, something which I've associated with devices not getting enough power based on prior results."

I think this has more to do with USB startup and shutdown process ("enumeration") than adequate power.

I would suggest you take a look at this post:
http://www.carnetix.com/forum/showthread.php?t=661
David has come up with a very nice, and repeatable solution for powering USB devices.

Also, as MikeB says, any relay will work as long as the contacts are rated for >500mA per connected USB device.

[s4per]

Hey Guys,

Thanks for the replys..I did some more tests last night, and it seems the cable is just not 'surviving' the cutting and soldering. Don't know why as it looks fine, but I'm not getting the right voltage at the extension cable...so that explains the problems and confirms both of your feedback that it really shouldn't be too little power based on what I have hooked up to it. I am confident, Mikeb, that it's USB 2.0 cables all around, but good thought.

The link to David's fix is great. I just want to confirm that it's the Dlink DUB-H7 (kinda' funny if it is as it's the hub I've had in my car for the last 3 years)? and - to cut the trace, do you just take a screwdrive across it or ..???

TIA,
I feel like I'm getting closer

-Per

[s4per]

OK, that worked.

Now - next issue ...secondary out shuts off IMMEDIATELY and screws up touch screen upon restarts.

I'll start another thread for that. EDIT- New thread here: http://carnetix.com/forum/showthread.php?t=692

Thanks all!

-Per