PC SIDE (USB Power) | RADIO SIDE (CI-V Bus Powered) | TXD ---> [ 470 Ohm ] --->|----+ +---[ 1k Ohm Pull-up ] ---> To Radio 5V* LED | | (Optional if radio lacks pull-up) | | |/ GND (USB) ----------------+ | --| Phototransistor | |\> | +-------------------------> To 3.5mm TIP | | +-------------------------> To 3.5mm TIP | |/ RXD <-------------------------+----| Phototransistor | |\> USB 5V ---> [ 4.7k Pull-up ] | | | +--->|--------------------> To 3.5mm SLEEVE | LED | | | +---[ 470 Ohm ]------> To 3.5mm TIP
Solder the cathode (the side with the black band) of the 1N4148 diode directly to the TXD pin of the USB module.
Launch your logging or radio control software (e.g., N1MM Logger, Logger32, WSJT-X, fldigi, or wfview ).
Check for TX and RX swapped at the transistor level.
: Install any necessary drivers on your computer. FTDI provides drivers that allow the USB interface to appear as a virtual COM port. icom ci v usb interface schematic top
Option B: The High-Performance Optoisolated Circuit (Top Recommendation)
Connects to the PC, usually via a standard USB-A or Micro-USB connector. Conversion Logic: TXD (Transmit) RXD (Receive)
For most users, a PCB based on the offers the best balance of speed, stability, and simplicity.
(Invoking related search suggestions...) PC SIDE (USB Power) | RADIO SIDE (CI-V
. Icom's CI-V bus uses a single-wire, bi-directional TTL (0–5V) signal where both transmit (TX) and receive (RX) data are combined onto one line. USB Controller FTDI FT232RL
A budget-friendly, compact alternative with excellent driver support.
Open your computer's (Windows) or type ls /dev/tty* (Linux).
: If using a pre-made CP2102 or FT232RL breakout board, identify the Solder the Bridge : Install any necessary drivers on your computer
Icom radios use a standard 3.5mm (1/8") mono phone jack for the CI-V port. The tip carries the shared bidirectional data signal, and the sleeve provides the common ground.
Place a signal diode (1N4148) on the TX line (cathode towards the plug tip) to allow the RX line to read the bus without interference. Pro Tips for Builders G3VGR's USB CI-V and Winkey Interface - QSL.net
Ham shacks are filled with stray Radio Frequency Interference (RFI). Without protection, RF energy leaking down the CI-V cable will crash your computer's USB controller during transmission.
The CI-V port is a 3.5mm mono jack that acts as a bidirectional, open-collector bus. TTL (0V to 5V or 3.3V). Wiring: Tip is Data, Sleeve is Ground.
The TXD pin connects through a 1kΩ current-limiting resistor to the anode of the internal LED inside the first optocoupler.
Once hardware assembly is complete, connect the device to your PC and radio to initialize communication. Driver Setup