To my surprise, I couldn't remember how to get the dang thing working with fldigi (http://www.w1hkj.com/) so I'm trying to capture that information here.
The interface cable I made apparently used the USB to RS232's RTS line to signal the radio to transmit (or virtually to push the PTT or push-to-talk button) so that was the first mystery. The second mystery was that I needed to use a "separate serial port" under the "hardware ptt" tab even though both USB devices turned out to be the same.
The green 8mm stereo jack line is my transmit audio cable and should be hooked up to the headphones or line out jack, a second separate 8mm stereo cable (not connected to the USB, green audio, or 13-pin accessory cable) needs to attach to the phones line on my front panel and it should hook up to the line in or microphone jack on my computer.
The black cable attached to the 13-pin accessory jack connector with an 8mm stereo connector is for the CV-I interface (multi-drop serial port that Icom uses to control radios) and hooks up in the back of the 706. It connects to the 8mm jack that is closest to the 8p8c (colloquially known as the RJ45 jack) used for the HM-103 mic.
The remaining black cable is the USB cable which is an RS232 serial emulator chip and cable and needs to be plugged into a free USB port, I'm assuming above that it's the only USB serial port you've plugged in otherwise the "device" might be /dev/ttyUSB1 or /dev/ttyUSB2 or something.
With the below fldigi settings, if you run fldigi and the radio isn't powered and the USB control cable isn't plugged into your computer, fldigi will not start! Once you plug in the USB cable and power the radio it will run.
Here is a summary of the settings I need for my interface cable:
Use Hamlib: checked
Rig: Icom IC-706
Device: /dev/ttyUSB0 (add yourself to the dialout group on Ubuntu to get permissions correct, else chmod 777 /dev/ttyUSB0 everytime you want to use it)
Baud rate: 19200
All other settings at defaults which are:
Retry interval: 1000
Write delay: 0
Post write delay: 0
PTT via hamlib command: unchecked
Audio on Auxiliary port: unchecked
DTR +12: unchecked
RTS +12: unchecked
RTS/CTS flow control: unchecked
XON/XOFF flow control: unchecked
CW is LSB mode: unchecked
RTTY is USB mode: unchecked
Sideband: Rig mode
Mode delay: 200
Polling Interval: 250
PTT tone on right audio channel: unchecked
h/w ptt device-pin
Use separate serial port PTT: checked
Use RTS: checked
RTS = +V: unchecked
Use DTR: unchecked
DTR = +V: unchecked
Use parallel port PTT: unchecked
PTT delays valid for all CAT/PTT types
Start of trasmit PTT delay: 0
PTT end of transmit delay: 0
While debugging all of this, occasionally the PTT button would get stuck "on" so I wrote this python script to force it back off:
#!/usr/bin/python3 import serial ser = serial.Serial() ser.baud = 19200 ser.port = '/dev/ttyUSB0' ser.setRTS(0) ser.setDTR(0) ser.open() ser.close()