The most robust way is to use a logic gate, such as the (a hex buffer) or a NAND gate configured as an inverter, to actively buffer and combine the signals. A more common and simpler approach is the "two-transistor" method, which is essentially building a basic open-collector interface.
If you prefer not to build, several commercial products are regarded as top-tier: Icom CT-17
The is a single-wire, TTL-level, half-duplex asynchronous serial protocol. Voltage: TTL levels (0V to 5V or 3.3V), not RS-232 (±12V).
When turning this schematic into a physical printed circuit board (PCB), pay strict attention to layout isolation:
Unlike standard RS-232 which uses separate Transmit (TX) and Receive (RX) lines, CI-V combines TX and RX onto a single bi-directional line. icom ci v usb interface schematic top
High-power transmissions can inject RF energy back into your computer, freezing your logging software or disconnecting the USB device.
The Icom CI-V (Communication Interface V) USB interface is a serial communication bridge that allows a computer to control amateur radio equipment. Modern designs typically center around a , which converts USB signals into the 5V TTL (Transistor-Transistor Logic) levels required by Icom's half-duplex single-wire bus. Core Design Principles
Electrical signals are converted into light inside the chip and passed across an physical gap to a light sensor.
Have questions about a specific component or layout? Join the r/amateurradio subreddit or the Icom CI-V discussion group on Groups.io – many experienced builders share their top-side PCB views and modifications. The most robust way is to use a
This design is ideal if you already have a standard USB-to-Serial (TTL) converter board (like those based on PL2303 or CP2102) and want to interface it with the single-wire CI-V bus. 2x 2N2222 or 2N3904 NPN transistors, 2x resistors, 1x
There are three primary "topologies" for a USB CI-V interface, each with its own schematic approach. The "top" view of your PCB or breadboard will depend entirely on which of these design philosophies you follow.
The output transistor side connects to the FT232RL RXD pin with a 4.7k-ohm pull-up resistor to the USB +5V. 3. The Bi-Directional Bus Combiner (Radio Side)
) TTL signal. This signal is fed into a simple single-transistor inverter (or a dual-diode steering circuit) to combine TX/RX into the single CI-V wire. Voltage: TTL levels (0V to 5V or 3
Data from CI-V bus to PC RXD.
: Solder the USB connector to the board and connect VCC and GND to the FTDI chip.
Developed in by Icom Inc. in Osaka, Japan, CI-V was actually the company's fifth attempt at a communication interface—hence the Roman numeral "V". Its original purpose wasn't just computer control; it was designed to allow separate receivers and transmitters to act as a single, unified transceiver.
Once your hardware is built, you need to configure your software.