The is the brand's protocol for remote control of its radios. Designed as a bidirectional bus, CI-V uses an asynchronous serial communication system at TTL voltage levels (+5 V for a logic "1", 0 V for a logic "0"). Virtually all Icom transceivers from the last few decades are compatible, which is why the CI-V system remains so popular.
On most Icom radios, the CI-V port is a , typically labeled "REMOTE" . The connector has two conductors:
(typically 4.7kΩ to 10kΩ) is connected between the data line and +5V to maintain the bus in a high state when idle. Radio Side: A shielded cable terminating in a 3.5mm mono plug . The tip is the data line, and the sleeve is the ground. Simplified Wiring Diagram For those using a pre-made USB-to-TTL adapter (like those used for Arduino), the wiring is even simpler: Connect GND: Adapter Ground right arrow 3.5mm Plug Sleeve. Combine Data: Tie Adapter right arrow 3.5mm Plug Tip. Add Protection: icom ci v usb interface schematic top
While commercial cables exist, building your own CI-V to USB interface is an excellent, low-cost weekend project. This guide provides a highly efficient, field-tested schematic design to link your Icom rig to any modern USB port. Understanding the CI-V Hardware Protocol
Include a small pinout graphic on the top silk showing and Sleeve = GND . Add status indicator LEDs to the top layer: TX LED (Red): Blinks when the computer sends data. RX LED (Green): Blinks when the radio responds. PWR LED (Blue): Indicates active USB bus power. 5. Construction and Troubleshooting Tips The is the brand's protocol for remote control of its radios
pins of the UART chip must be tied together to interface with the single-wire CI-V bus.
Unlike standard RS-232 serial interfaces that use separate Transmit (TX) and Receive (RX) lines, . The Connector: A standard 3.5mm mono phone jack. On most Icom radios, the CI-V port is
: It uses a standard asynchronous serial format (NRZ).
This circuit diagram breaks down the components inside the "CI-V Level Shift" block. It is a bi-directional level converter and bus interface.
The most efficient DIY design uses a common USB-to-Serial board (like those based on , CP2102 Go to product viewer dialog for this item.
One of the most documented and frequently cited homebrew projects is . This design is a "top schematic" in the best sense: it combines a USB‑to‑TTL converter (FTDI DLP-2232M), a 7417 buffer, and additional support for PTT and a Winkey keyer. Because all components run from the USB +5 V bus, no external power supply is needed.