: For those using a basic USB-to-TTL adapter, a simple circuit using two transistors can combine the TX and RX lines into the single-wire CI-V bus.
The ICOM CI-V USB interface works by converting the CI-V signal from the ICOM radio to a digital signal that can be transmitted over USB to a computer. Here's a step-by-step explanation of the process:
Whether you are a homebrewer or a contester, mastering the CI-V bus through a proper USB interface opens the door to digital modes, logging, remote operation, and full station automation.
| Requirement | Why it matters | |-------------|----------------| | | CI-V is a shared bus; multiple devices can drive it low. A standard totem-pole output would short-circuit. | | Pull-up resistor (~4.7kΩ) | Ensures CI-V line idle high without current drain. | | Diode protection | Prevents CI-V voltage (5-12V accident) from back-driving FTDI chip. | | No ground loops | The interface should have opto-isolation (advanced) or at least common ground – but a direct ground is acceptable for single radio. | | Inversion as per Icom spec | Without correct inversion, commands will be byte-swapped or corrupt. |
Tie a from the 3.5mm Tip line to the 5V VCC line. icom ci v usb interface schematic top
+5V (From USB) │ ├──────────┐ ▼ │ ┌───────┐ [R1] 4.7kΩ │ │ │ │ FTDI │ ├───────────────● Data (Tip) ──► To Radio │FT232RL│ │ │ (3.5mm Jack) │ │ │ D1 1N4148 │ │ TXD ├──────┼─────►|────────┤ │ │ │ │ │ RXD ├──────┴───────────────┘ │ │ │ GND ├─────────────────────────────────────► GND (Sleeve) └───────┘ Circuit Operation Explained
Once hardware assembly is complete, plug the interface into your PC. Most modern operating systems will instantly recognize an FTDI or CH340 chip and assign it a COM port.
Use software like Eagle or KiCad to create a compact PCB, often designing the "schematic top" layout to fit into a small enclosure or even inside a 9-pin D-shell connector.
Open your logging or digital mode software (such as Ham Radio Deluxe, Flidigi, or WSJT-X). Software Settings: Rig: Select your specific Icom model. COM Port: Select the assigned COM port. : For those using a basic USB-to-TTL adapter,
Because it is a shared bus, data sent by the PC is immediately seen by the PC's own receiver. Software designed for Icom radios expects this local echo and handles it automatically. Schematic Architecture: USB-to-UART with Optoisolation
Wrap the USB cable around a . Keep the interface enclosed in a shielded metal box .
Solder the cathode (striped side) of a to the board's TX pin.
Searching for isn’t just about finding a random circuit diagram—it’s about understanding the topology that guarantees reliable, RF-immune computer control of your Icom radio. By following the principles and schematic blocks outlined in this article, you can build a professional-grade interface that outperforms many commercial units. | | Diode protection | Prevents CI-V voltage
The CI-V bus is an , bi-directional, single-wire system operating at TTL (5V) logic levels .
Enable the internal pull-up or solder a physical between the RX pin and the board's VCC (5V) pin. 2. Eliminating RFI (Radio Frequency Interference)
Below is the conceptual schematic layout for the interface. It is divided into the and the Radio Side (Rig Powered) .