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dreaming is offline dreaming
2006-01-12 , 02:53
Posts: 27 | Thanked: 0 times | Joined on Dec 2005
#31
Originally Posted by Simon
OK. I put some pics of my little powered USB box up at http://www.asciimation.co.nz/770

The page is really crappy but hey, it's 1 am here and I should be asleep!

I haven't tested it fully yet since I am am waiting for the batteries to be fully charged first.

I can't really provide full instructions since 1, I made it up as I went along and 2, it doesn't need to be this complicated. I just like an excuse to waste time making gadgets!
Awsome! Nokia owes you some cash.
 
Mike Cane is offline Mike Cane
2006-01-12 , 04:53
Posts: 949 | Thanked: 14 times | Joined on Jul 2005
#32
Originally Posted by JMills
I'm a bit surprised that either of these (USB Type-A socket to Type-A socket "gender changer" and the hub) work... it suggests that certain USB _peripherals_ (hubs, etc...) are providing power on the upstream side, which IIRC is a violation of the USB spec.
This is also why the entire affair is so confusing to non-EEs like me.

I appreciate all the efforts people have made to get things to work with the 770's port. Heroes all.
 
Simon is offline Simon
2006-01-12 , 06:08
Posts: 191 | Thanked: 9 times | Joined on Nov 2005
#33
Excellent! It's not a paperweight! Using instruction in the forum I just tried mounting my USB pen drive and that worked! It seems to appear as /dev/sda. I was able to link it to /home/user/MyDocs then fire up FileManager and there was the pen drive in the view. I was able to play a random MP3 and some film clips I had sitting on the pen drive even. Can't wait until my keyboard arrives to try. Thanks to everyone for all their tips and hints to get this to work!

One thing I noticed (and I don't recommend doing this!) is I switched off my little box halfway through playing a MP3. It reverted back to being able to read the MMC card which is good and I was then able to switch it back on and the pen drive appeared again automatically. But then when I played that MP3 it stoped halfway! At the same point as when I unplugged it in fact. I also tried unplugging the pen drive then plugged it back in and it said there were no files on it. I turned off the 770 and then restarted it with everything connected and remounted and relinked the drive and it all works again so no permanent damage done.

Like with any computer I don't recommend plugging or unplugging things whilst they are being accessed! The little LED on the pen drive seems to flash the whole time it is connected to the 770.

I will set up some scripts I can run in Xterminal to make all this stuff easier to do. I already have those set up to tun on and off host mode. What I would really love to do is write apps that run from the desktop to do all that. Is that possible? Better start learning how Maemo works I guess.

Simon
 
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meshsmooth is offline meshsmooth
2006-01-12 , 12:46
Posts: 32 | Thanked: 2 times | Joined on Oct 2005 @ australia
#34
my curent isues are with not being able to mount the drives as user, not because i cant gainroot but the interface operates as user, so if you want save files using the gui you need write acess as a user. the ohter isue is it mounts as dos file system meaning only 8 character names. any ideas on fixing this?
Last edited by meshsmooth; 2006-01-12 at 12:48.
 
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CrossBow is offline CrossBow
2006-01-12 , 14:01
Posts: 58 | Thanked: 5 times | Joined on Dec 2005
#35
As one of the "inventors" who has made a back-feeding battery powered USB Hub, I would like to report a discovery, and a small note of caution.

Appearently, Low batteries in these devices cause crashes. When I first built mine, I used whatever "AA" batteries I found lying around. It seemed to work fine with several keyboards and several flash drives, but a Dell Multi-media keyboard would crash the 770.

A few days later, I started getting crashes using the Apple keyboard that I had been using for days.

Suspecting the batteries, I changed them with a fresh set. Now even the Dell Keyboard works fine.

Doing some testing, I found that the Dell keyboard reports itself as wanting 100ma (hub) + 50ma (keyboard) = 150ma from the USB bus. The Apple reports 50ma (hub) + 50ma (keyboard) = 100ma total. The Dell keyboard has a bunch of LED's that are lit anytime it is plugged in.

BTW, the LED on my batterypack/hub combination was bright at all times.

So all you USB power hackers may want to save your work often as the batteries get low.
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Mike Cane is offline Mike Cane
2006-01-12 , 14:06
Posts: 949 | Thanked: 14 times | Joined on Jul 2005
#36
Originally Posted by Simon
I will set up some scripts I can run in Xterminal to make all this stuff easier to do. I already have those set up to tun on and off host mode.
Clarify this. Do you mean you can now switch between host/client at will, without reflashing every time?!
 
bhima is offline bhima
2006-01-12 , 15:44
Posts: 79 | Thanked: 1 time | Joined on Nov 2005
#37
Originally Posted by CrossBow
Appearently, Low batteries in these devices cause crashes.
Did you build in any regulation or not? I'm planning to build a battery powered one to complement my current externally powered unit, and would obviously like to avoid the crashing problem. I'm hoping that a regulator which simply cuts out totally rather than slowly drops the voltage will help fix that.

Another issue to be aware of is that you are violating the USB spec if you provide live data to a device without providing power first - USB cables are designed to ensure you get power first. I don't know if this will cause damage, but some semiconductors are unhappy if you do that.
 
Simon is offline Simon
2006-01-12 , 17:06
Posts: 191 | Thanked: 9 times | Joined on Nov 2005
#38
Originally Posted by bhima
Did you build in any regulation or not? I'm planning to build a battery powered one to complement my current externally powered unit, and would obviously like to avoid the crashing problem. I'm hoping that a regulator which simply cuts out totally rather than slowly drops the voltage will help fix that.

Another issue to be aware of is that you are violating the USB spec if you provide live data to a device without providing power first - USB cables are designed to ensure you get power first. I don't know if this will cause damage, but some semiconductors are unhappy if you do that.
Given what you say I might remove the power switch from mine. It is unessary anyway. If I can I might put in a low current LED that switches off when my battery voltage drops too low. Maybe using a zener somehow? Tricky with NiMH since when considered flat they are still giving out about 1.1 volts I think? I tbelieve most regulators like 7805s and so on just stop regulating when the input voltage drops too low rather than switch off. They need so many volts above the regulated output to keep regulating. When the input voltage drops below their cut off point you just get out what goes in. I used a low drop out type (2940 from memory) which regulates down to .5 a volt above rated. So my 5 cell NiMH battery will give say 6 volts fully charged (actually more) and 5.5 volts flat which is where the regulator stops regulating anyway. I need my LED to turn off then so I know to recharge it.

Be aware I an not an EE! I am just a tinkerer Things I say or do probably make real EEs cringe! I am actually a low drop out EE. I did the first year of the EE degree then changed to computer science. Much less maths!

Mike, there are instructions on how to enable and disable host mode from within a terminal with a Linux command but you need to have root access to do so. I am a little rushed now or I would post the links for you but if you search the forum for the text 'echo host >' you should find the relevent posts.
 
Simon is offline Simon
2006-01-12 , 17:34
Posts: 191 | Thanked: 9 times | Joined on Nov 2005
#39
Oh, can't take the switch out to put in an LED because I would still need a switch since otherwise the LED will be the thing draining the battery!

Mike, that enabling host mode on the fly was posted by Aaron here: http://www.internettablettalk.com/f...p=6622#post6622
 
bhima is offline bhima
2006-01-12 , 19:57
Posts: 79 | Thanked: 1 time | Joined on Nov 2005
#40
Originally Posted by Simon
If I can I might put in a low current LED that switches off when my battery voltage drops too low. Maybe using a zener somehow? Tricky with NiMH since when considered flat they are still giving out about 1.1 volts I think?
I don't remember the exact numbers, but that's about right. The voltage of a battery is constantly lowering as you draw power from it.

When it's "dead" is not really an absolute, precise number. However, if you lower the voltage beyond a certain point, you will damage the battery...

I think your circuit ideas may be reasonable, but I'm not sure what is normally done. I'm planning to use a fancier DC/DC switched mode converter.

Originally Posted by Simon
I did the first year of the EE degree then changed to computer science. Much less maths!
When I started at Carnegie Mellon, the degree they offered was "Math/Computer Science." From what I've seen, CS at Carnegie Mellon actually involves more math than EE. It's a lot more symbolic, with a lot more discrete math and combinatorics. You see less numbers, but more math.
 
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