Once built, plug the interface into your PC. Windows, macOS, and Linux usually install FTDI or CH340 drivers automatically.
Building your own Icom CI-V USB interface is an excellent, cost-effective project. Using the schematic above with an FTDI chip provides reliable rig control, allowing you to unlock the full potential of your Icom transceiver.
The USB-to-TTL adapter provides the +5V power and ground for the circuit. The critical part is the "CI-V Level Shift" block, which manages the bidirectional communication.
Open your radio control software and configure the following parameters: Select the newly assigned virtual COM port.
Note: This configuration causes the computer to "hear" its own echoes. Most software, like Omni-Rig, Ham Radio Deluxe, or fldigi, handles this automatically. icom ci v usb interface schematic top
(standard headphone jack size). Data is sent and received over the same wire, making it a half-duplex system. Core Schematic Components A modern USB-to-CI-V interface typically centers around a USB-to-UART bridge chip , such as the FTDI FT232RL
However, building from a top-quality schematic gives you complete control over isolation quality, component choice, and cost (under $15).
Because CI-V is a "half-duplex" single-wire system (the radio and the computer take turns talking on the same wire), you cannot simply tie the TX and RX pins directly together without risk of contention. However, with FTDI chips, there is a trick:
To help me tailor any further technical advice, please let me know: Once built, plug the interface into your PC
Before building the circuit, it helps to understand how Icom's communication protocol operates.
[ PC USB-TTL Side ] [ Icom Radio Side ] TXD o----[ 470 Ohm ]----+ +----o CI-V Tip (Data) | | +-----+ +-----+ | LED | | Photo| +-----+ |Trans| | +-----+ GND o-------------------+ | +----o CI-V Sleeve (GND) RXD o-------------------+ +----o CI-V Tip (Data) | | +-----+ +-----+ |Photo| | LED | |Trans| +-----+ +-----+ | VCC o----[ 4.7k Pull-up ]+ +----[ 470 Ohm ]---o CI-V Tip (Data) Use code with caution. How it works: This circuit uses two optocouplers (e.g., or 4N35 ).
Combines separate TX and RX lines into a single, bi-directional data line without causing a feedback loop.
USB SIDE (Non-Isolated) | RADIO SIDE (Isolated) | +-----+ +-----------+ | +------------+ | |--TX-->| |--Isol. TX---|--+---| Steering | 3.5mm Jack | USB | | Digital | | | | Diode | /| | Chip| | Isolator | | \ | Network |----| |--- TIP (CI-V) | |--RX--<| |<-Isol. RX---|--+---| | | | +-----+ +-----------+ | +------------+ \|--- SLEEVE (GND) | | | | | GND GND1 | GND2 GND2 The Steering Diode Network Using the schematic above with an FTDI chip
Ensure your software (e.g., HRD) uses the correct hex address (e.g., 94h for IC-7300, 4Eh for IC-706).
If you have decided to build your own interface, following a set of methodical steps will save you hours of debugging.
Integrating an Icom transceiver with a modern computer requires a CI-V (Computer Interface Five) adapter. Most modern laptops and desktops lack native RS-232 serial ports, making a USB-to-CI-V interface essential for digital modes, logging software, and remote rig control.
Building Your Own Icom CI-V to USB Interface: A Complete Schematic Guide