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I'm using adafruit's usb to ttl gadget to communicate with my raspberry pi over usb. For some reason when I plug in my Raspberry Pi Ralink RT8188 wifi dongle and reboot, I can't access my raspberry pi over usb anymore. I use screen like this to access my raspberry pi:

screen /dev/ttyUSB0 115200

Any reason why I can't access my raspberry pi over usb when I am using a wifi dongle?

EDIT: dmesg output before WiFi.
Output of lsusb before WiFi:
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub.
dmesg output after WiFi.
Output of lsusb after WiFi:
Bus 001 Device 003: ID 148f:7601 Ralink Technology, Corp. Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

It seems like it kindof works when having the wifi dongle, except the output is totally broken (logged in and ran command ls):

 p
oi
rasp
rapbein:pi
Password:
Las in: r22 :1:5C  nnux rasberrypi 4.-c5+c 206lgrm dwte Nettonor oge in ursaedo*cop.
               bRRANTY, to the extent
permitted by appliable law.
piaspberrypi:~$    tmp   wa.ln.y pw.y      etp wirngi78bc
  • I think there are some diagnostics that will be useful to examine. First, let us compare to outputs from dmesg ... one with the WiFi attached and one without. Next, let us see the output for lsusb ... again ... one with the WiFi attached and one without. – Kolban Jan 22 '16 at 19:50
  • @Kolban I have added some more information. It turns out that I can actually "use" the serial console but as you can see from the output above it is very buggy when using the wifi dongle. – Linus Jan 22 '16 at 20:10
  • What I find very interesting is that the Adafruit USB device doesn't show up in your USB device list in either story. Was the UART device plugged in when you ran lsusb? – Kolban Jan 22 '16 at 21:39
  • Another thought ... what if we reduced the baud rate? 115200 is fast and what is needed for transferring large binaries ... but if what we are doing is terminal interaction, we might get away with a lot lower speed ... try with 9600. – Kolban Jan 22 '16 at 21:44
  • @Kolban why would the serial console show up as a USB device on the raspberry pi? It is plugged in on the gpio. lsusb was issued on the rpi itself, not on the host computer to which I plugged in the "USB end" of the device. I'll try decrease the baud rate. – Linus Jan 22 '16 at 22:24
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Since the USB to TTL serial is sort of working it is probably safe to rule out software configuration problems in the OS. I can think of 2 possible causes:

  1. Your power supply is not big enough. Try a different supply rated for more current.

  2. The radio signal from the WIFI adapter is somehow interfering with the USB or TTL serial signal. Two possible fixes: try reducing the speed of the serial connection or try moving the USB->TTL cable so it is farther away from the WIFI dongle.

You could try both fixes at once by moving the dongle to a powered USB HUB some distance from the Raspberry Pi.

  • I am using the offical raspberry pi psu with 1 A, and the usb to ttl serial cable is getting its power from my host computer and I have nothing else connected to my raspberry pi (A+). I don't have a usb hub available right now, but it did work better it seems when I used a usb extended, but that might've been a coincidence. – Linus Jan 23 '16 at 12:00

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