Technology Musings by John Spade
iPad USB charging hack
Last Updated on Wednesday, 28 July 2010 13:40 By:
ADVANCED: This article describes how to update your USB drivers on certain systems to allow higher current charging if only one device is plugged into that group of ports. I will be updating this as i go along but this works on my PC's with ASUS motherboards ( ASUS and HP ) and so far it is working on my Lenovo Thinkpad T400. This may provide the perfect marriage with the Y USB power splitter cables. If anyone has pinout for one of these cables, please contact me. Amazon and other vendors sell such cables but I'm curious as to the construction. Just marrying the +/- 5V does not appear to be correct. DISCLAIMER: warning, there is a chance that this could burn out your USB port or device, though most good boards should protect themselves. Not responsible for damages, no warranty expressed or implied, risk of fire, etc.
This seems to work on boards with Intel ICH9 and 10 chipsets. ASUS has published a driver update that seems to work on some boards with Intel USB root hubs. I have not tested it yet with the iPad battery below 80% where it would draw more power but it worked in the top end. I was able to have the device awake playing Pandora and it shows charging AND the battery level increased. When I attempted to plug it into a port where there was another USB device on the same 'hub' it disabled the internal hub and both devices lost power. Was able to reset it and separated out all my devices.
iPad Charge Cable
Last Updated on Wednesday, 28 July 2010 09:31 By:
Some people have noticed that the iPad will not charge on some after market cables, especially if they are longer than the standard charge and sync cable. In fact I have seen this on standard length cables where the iPad battery drops even though I have it plugged into the 
charger it came with and it says charging.
The reason for this is pretty simple. USB charges around 5 volts and if you are expecting the over 1 amp ( 5 watts ) on the standard cable, it better not be very long. This is because the size / gauge / AWG / diameter of the wires is too small. By specifications, USB 2.0 cables can have wires with AWG as high ( small ) as 28.
First a table of solid core wire AWG for power transmission ( most USB cables have stranded wire for more flexible cables ). The following is a table that shows common iPhone or iPad charging methods, for nerds the values are approximate and designed to carry the 'concept' and length is length of cable but AWG for true 'round trip'. Smaller AWG means a thicker wire. Data from Powerstream calculator.
| Charger | Current/Power | 3ft AWG | 6ft AWG | 10ft AWG | Approx Voltage Drop |
| PC USB | 0.5A/2.5Watts | 28 | 26 | 24 | 0.4 |
| iPhone 3GS | 1.0A/5.0Watts | 26 | 24 | 22 | 0.5 |
| iPad | 2.1A/ 10Watts | 22 | 20 | 18 | 0.5 |
iPad charging and cables
Last Updated on Friday, 16 July 2010 08:35 By:
The iPad needs more current to charge. Not a big surprise. What is surprising is that Apple did not include ( or accessorize ) a USB power injector that allows you to sync and charge at the same time. The iPad will charge slowly off USB if the screen is off and seems to stay about even if the screen is on and hooked to a computer USB.
It also appears that some aftermarket or longer cables will not charge the iPad even if plugged into the included 10 watt power cube. I assume this is due to more resistance on longer cables or cheaper or inferior wires on the aftermarket cables. What is very strange is that it seems to happen on older geniune Apple cables also. The Apple Store only sells one 'universal' cable, so perhaps the current one is better.
The dual ended USB cables commonly used to power portable USB hard drives do not seem to help much with iPad charging. This is probably due to negotiations and safety built into the iPad so that it doesn't over draw from the USB ports and burn them out.
Finally, the slow sync and backup issues with the iPad and different cables. There may be something to this. According to the USB specifications, different data rates are allowed at different charge rates. This could be to avoid inductive noise when more power is transiting the cables or it could be to not tax circuits that are being forced to provide current and transmit data. It seems that a longer or inferior wire would lower the line voltage due to resistance and thus increase the amperage drawn. This may be the reason the data rate drops. Or not.
I can say that I have seen the battery drop when plugged into the 10 watt brick while using it with some cables. I switched cables and it began charging. Both times it showed to be charging. Disassembly of an Apple cable shows very small gauge stranded wires. Thinking of trying to build a custom cable with more robust 5V and ground wires, just to see.
iPhone iOS4 and Exchange Server
Last Updated on Friday, 16 July 2010 08:34 By:
Apple has published a fix/patch that may help with any some iOS4 issues you have on your iPhone 3G, 3GS, or 4 for those of you who updated software or phones. Rather than do this and by combining what I leared from Apple, I made a change on my Exchange 2007 configuration that seems to have helped based on information in this link from Microsoft. I lowered my minimum heartbeat time from 60 to 30 seconds and this seems to have helped, or I seem to be able to send attachments now. I am guessing that large attachments may fail still. Problem seems to occur on iPad iOS 3.2 also, but less frequently.
If your company assigns a .local domain via VPN then it will fail also as wireshark seems to show it trying to multicast with no failover ( or maybe just timeout ) to unicast addresses. It looks like Apple has a RFC out for this but seems like poor judgement to implement it in production.
[update]
Wondering if apple did any testing at all with enterprise users.
watch world cup on iphone / ipad
Last Updated on Friday, 16 July 2010 08:34 By:
espn3.com is streaming the world cup games live but it won't work ( currently ) on Apple devices such as iphone, ipad, or ipod touch. Orb has been kind enough to fix this with these instructions. It is $9.99 for the app, but pretty handy for other streaming to your iDevices also. I have used it for some time to watch live shows when travelling as it allows you to stream at different rates. What is nice about this solution is that you do not need a TV tuner card for it to work.
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