Raspberry pi Project, powering it with a USB hub through one cable. AKA Back-powering
Made a step in my project to Integrate a RasPi A Model with a USB Hub as a co-unit. Removed the Dual USB connector from RasPi #1. I hardwired two USB cables directly to the board. The Gray cable has a Mini USB connector to connect to the USB hub. The Black cable is to a Female USB A connector. I did not want to lose a USB port. I now have 4.73V at TP1/TP2 instead of 4.35V. I also removed the 700ma polyfuse from F2 and replaced it with a solid wire jumper.
Just plugged in my Linksys WUSB54GC WiFi. Network Manager shows it as connected. disconnected the wired. Wifi is running off of F1 no reset. It is connected. When I attach a USB stick to that cable my voltage drops to 4.76v. I do not experience a reset while plugging or unplugging the memory stick. I also can hotplug the USB HDD without a reset. I could not hot plug anything before, so I am considering this experiment successfull.
The next step will be to remove the Mini USB connector from the hub side (gray wire) and hardwire it also. Then I will remove the hub case and stack it under the RasPi. this will then be a single unit. At that time it will lose the Micro USB connector too. I could also remove F3. So basically I have 5 USB ports right now with 4 full, 2 to USB HDD, 1 for keyboard/mouse wireless combo and 1 (on RasPi) for the WiFi. The gray wire can also be used a port, but is lost when used with the hub.
I will work on it some more before next week. Really cannot wait for an A Model to try it all out with. I am worried that the new revision to the PCB could cause me to start all over. The 0 ohm resistors are even gone now. So adding a little resistance back into the USB, to stop reset problems, is not going to be easy now. But it wouldn’t be a challenge if it was all easy. The A model should be perfect for a Lapdock and Wifi on a single Micro USB female to A male cable. No more playing with adapter cables. I guess you could put an inline switch in the cable to turn the RasPi off.
I have installed the USB powered Raspi in a Deaths Head Pencil Box. Also inside is the Modified USB Hub and a USB HDD. Everything is powered by the USB hubs power supply, aq 5V 2A wall wart.
This is a top view with the RasPi on and working. The usb wires come from underneath. The black wire (top of board at USB) is a female USB dongle. This gives this RasPi a total of 5 USB ports.
This is a bottom view the pads where the original Mini USB connector was were just too small for me to work with. I soldered the Data wires on top of the diodes that led to the connector. The Power and Ground werre brought up near the power connector. The power wire is soldered to the output side of the hubs polyfuse, the ground is soldered to the connector ground post pad.
This RasPi now has 1/10″ pin headers install now. these are much more convenient than the hardwiring is. The USB holes are not 1/10″ spacing, but with a little wiggling you can get them in. the pins will be splayed out some. Then I soldered them in place. Next I bent them up straight. Then I built some connectors to attach to them.
I did have some trouble with this RasPi though. This was the 4th time I had soldered to the board and there was a lot of flux build-up around the USB port area. When I tested the board the USB was dead! I then went to RasPi #2 and installed pins on it. It worked just fine. I found I could SSH into RasPi#1. So the USB was not fried. I removed the front set of pins and inspected the board. In the build-up there was small pieces of solder, lots of them. I used a mild brush and some rubbing alcohol (50%) to scrub the area clean. I also used a wooden toothpick to scrub, between the pins and over those USB traces, that go between the pins on the top and on the bottom. I then retested it. It now works just fine. I reinstalled the other set of pins and now it is a backup to RasPi#2!
You can use a 8 pin, or two 4 pin connectors to connect to the pins. I also have used old 4 wire CD-ROM audio cables as connectors.