A low cost home made USB CI-V interface with open collector and solid Windows drivers

This article describes an inexpensive USB adapter for Icom's CI-V interface.

There are four common options for USB-serial adapters:

  • Prolific;
  • FTDI;
  • WCH; and
  • Silabs.

This article describes an adapter based on an inexpensive FTDI adapter (~$5 on eBay).


You will need the module, a Schottky signal diode (eg 1N5711), wire and a 3.5mm TRS plug or two. I have connected two plugs, one wired for TS (CT-17) and one for RS (OPC-478x).

The FT232RL chip used does not have open collector output, and the CI-V specification for half duplex on one wire requires that the tx output is open collector… so we will synthesise that with the diode. (Be aware than many / most ham designs are NOT open collector.)

Make a 6way header socket to go on the board assembly or wire directly to the PCB contacts. The diode is connected anode to rx, cathode to tx, and the rx wire is connected to the radio interface along with gnd.

Prepare the ends of the cable and attach the 3.5MM TRS to one end, centre conductor to the Tip, shield to Sleeve.


There you go, all done.

For the IC7410, the CIV interface uses TS of the TRS cable (CT-17 like), but some Icom radios share the external speaker jack for CI-V and in that case it is RS of the TRS cable (OPC-478x like).