OctoPi doesn't see the printer

#1

What is the problem?
With OctoPi installed and running, the Pi doesn't see the printer (Ender 3).

What did you already try to solve it?
I've tried switching through 4 different USB cords, 2 Pis (a 2B and 3B), and connecting to a different power source (and even tried switching the printer to a different power source). None of this has allowed me to connect to the printer.

Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...)
Currently have OctoPrint 1.3.11 connected to an Ender 3 1.1.6 with stock firmware.

When the printer is powered on, octoprint doesn't see it at all (in the octoprint log, it never acknowledges a port is plugged in). When the printer is off, if I don't block the pin in the USB cord (so the printer 5V is powered by the Pi), octoprint does see the printer on /dev/ttyUSB0, but cannot connect.

Here's the OctoPrint log from the latest powered-from-USB run (after the two web links that keep giving me posting errors):

2019-05-14 20:16:30,420 - octoprint.server.util.sockjs - INFO - Client connection closed: ::ffff:192.168.1.102
2019-05-14 20:16:31,886 - octoprint.server.util.sockjs - INFO - New connection from client: ::ffff:192.168.1.102
2019-05-14 20:16:32,043 - octoprint.server.util.flask - INFO - Passively logging in user dummy from ::ffff:192.168.1.102
2019-05-14 20:16:46,809 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Detecting serial port"
2019-05-14 20:16:46,876 - octoprint.util.comm - INFO - Changing monitoring state from "Detecting serial port" to "Error: Failed to autodetect serial port, please set it manually."
2019-05-14 20:16:47,731 - octoprint.plugins.tracking - INFO - Sent tracking event commerror_autodetect_port, payload: {'commerror_text': 'Failed to autodetect serial port, please set it manually.'}
2019-05-14 20:17:06,461 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Detecting serial port"
2019-05-14 20:17:14,806 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Detecting serial port"
2019-05-14 20:17:15,065 - octoprint.util.comm - INFO - Changing monitoring state from "Detecting serial port" to "Error: Connection error, see Terminal tab"
2019-05-14 20:17:15,101 - octoprint.util.comm - ERROR - Unexpected error while connecting to serial port: AUTO IspError: ''Timeout'' @ comm.py:_openSerial:2611 (hook default)
Traceback (most recent call last):
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/comm.py", line 2611, in _openSerial
serial_obj = factory(self, self._port, self._baudrate, settings().getFloat(["serial", "timeout", "connection"]))
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/comm.py", line 2579, in default
port = self._detect_port()
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/comm.py", line 2560, in _detect_port
programmer.connect(p)
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/avr_isp/stk500v2.py", line 34, in connect
self.sendMessage([1])
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/avr_isp/stk500v2.py", line 108, in sendMessage
return self.recvMessage()
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/avr_isp/stk500v2.py", line 119, in recvMessage
raise ispBase.IspError("Timeout")
IspError: 'Timeout'
2019-05-14 20:17:15,997 - octoprint.plugins.tracking - INFO - Sent tracking event commerror_connection, payload: {'commerror_text': 'Connection error, see Terminal tab'}
2019-05-14 20:17:23,275 - octoprint.util.comm - INFO - Changing monitoring state from "Detecting serial port" to "Error: Connection error, see Terminal tab"
2019-05-14 20:17:23,303 - octoprint.util.comm - ERROR - Unexpected error while connecting to serial port: AUTO IspError: ''Timeout'' @ comm.py:_openSerial:2611 (hook default)
Traceback (most recent call last):
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/comm.py", line 2611, in _openSerial
serial_obj = factory(self, self._port, self._baudrate, settings().getFloat(["serial", "timeout", "connection"]))
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/comm.py", line 2579, in default
port = self._detect_port()
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/comm.py", line 2560, in _detect_port
programmer.connect(p)
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/avr_isp/stk500v2.py", line 34, in connect
self.sendMessage([1])
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/avr_isp/stk500v2.py", line 108, in sendMessage
return self.recvMessage()
File "/home/pi/oprint/local/lib/python2.7/site-packages/octoprint/util/avr_isp/stk500v2.py", line 119, in recvMessage
raise ispBase.IspError("Timeout")
IspError: 'Timeout'
2019-05-14 20:17:24,001 - octoprint.plugins.tracking - INFO - Sent tracking event commerror_connection, payload: {'commerror_text': 'Connection error, see Terminal tab'}
2019-05-14 20:17:59,772 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Opening serial port"
2019-05-14 20:17:59,788 - octoprint.util.comm - INFO - Changing monitoring state from "Opening serial port" to "Connecting"
2019-05-14 20:18:33,193 - octoprint.util.comm - INFO - Changing monitoring state from "Connecting" to "Offline"
2019-05-14 20:23:09,174 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Opening serial port"
2019-05-14 20:23:09,184 - octoprint.util.comm - INFO - Changing monitoring state from "Opening serial port" to "Connecting"
2019-05-14 20:23:42,592 - octoprint.util.comm - INFO - Changing monitoring state from "Connecting" to "Offline"
2019-05-14 20:28:36,589 - octoprint.server.heartbeat - INFO - Server heartbeat <3
2019-05-14 20:29:14,209 - octoprint.plugins.tracking - INFO - Sent tracking event ping, payload: {'octoprint_uptime': 930}

And without the USB power:

2019-05-14 20:38:39,361 - octoprint.server.preemptive_cache - INFO - ... done in 9.11s
2019-05-14 20:39:47,999 - octoprint.server.util.sockjs - INFO - Client connection closed: ::ffff:192.168.1.102
2019-05-14 20:39:49,450 - octoprint.server.util.sockjs - INFO - New connection from client: ::ffff:192.168.1.102
2019-05-14 20:39:49,609 - octoprint.server.util.flask - INFO - Passively logging in user dummy from ::ffff:192.168.1.102
2019-05-14 20:41:51,650 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Detecting serial port"
2019-05-14 20:41:51,702 - octoprint.util.comm - INFO - Changing monitoring state from "Detecting serial port" to "Error: Failed to autodetect serial port, please set it manually."
2019-05-14 20:41:52,635 - octoprint.plugins.tracking - INFO - Sent tracking event commerror_autodetect_port, payload: {'commerror_text': 'Failed to autodetect serial port, please set it manually.'}

#2

Hello,

This link may be of help to you