I built this CI-V interface and the additional circuitry to provide PTT from RTS so I could interface my Icom IC-7000 to my computer to run the digital modes using FLDigi. This circuit comes from G3VGR. I built it using manhatten style construction, which is amazingly fast way to build up a project.
Photo of the computer connections. Standard DB-9 for the serial port connection with RCA jacks for soundcard MIC and SPEAKER input. My computer, probably like most newer computers, doesn't have a serial port. I use a generic run-of-the-mill USB->Serial converter.
Example FLDigi Configuration
Taking a look down from the top, you'll see the circuit isn't all that complicated. The big white squares are isolation transformers from old computer modems. Keeps my multi-megabuck radio from direct electrical connection to the soundcard.
CI-V Interface Overview
Manhattan construction for building projects is very easy to do. Mainly just punch out some PCB material into little circles using a hand punch for metal. Use super glue to mount it to a larger board. I had perfboard on hand but you could use an unetched PCB board as the base. The latter is what you really want to use because it creates a very nice ground plane. At audio levels, I didn't need a significant ground plane so I used a strip of PCB material to create a central ground.
That's about it for this project. Can be completed in about an hour! Total cost, $2. Bought the case at the swapmeet.
Slightly Blurry Close Up of Manhattan Construction.
The radio connections use a 6-pin mini-DIN connector. Now, don't go all crazy and buy an expensive brand new connector, just find an old busted keyboard that has a mini-DIN connector on it and cut it off right where it enters the keyboard. Ring out the wires so you know which color goes to which pin. The CI-V remote control jack uses a standard 1/8" 3.5 mm plug.