Looking for IR Capture cable schematic diagram to build my own cable for use in IRScrutinizer.

Preferably for a serial port but a USB cable schematic will also do as I have a few USBtoTTL cables lying around.

Any help is greatly appreciated.

I am not sure if there is a misunderstanding here; IrScrutinizer captures irsignals with a device of some sort, not with a "cable". The ones supported are IrWidget, GlobalCache, IrToy, Arduino, CommandFusion. The current development version [Link: github.com] adds support for /dev/lirc (on Linux) and replaces "Arduino" by general "Girs client". For more details, see the documentation, or ask.

You may try this: [Link: harctoolbox.org]