Icom Ci V Usb Interface Schematic Top Verified

The TXD pin connects through a 1kΩ current-limiting resistor to the anode of the internal LED inside the first optocoupler.

The core challenge in building a CI-V interface is the electrical incompatibility. A standard computer's USB port outputs clean (typically +5V to -5V or +12V to -12V) on its serial communication lines, and these lines are dedicated transmit or receive. As explained above, the CI-V bus uses TTL levels on a single, bidirectional line with an open-collector driver.

High-power transmissions can inject RF energy back into your computer, freezing your logging software or disconnecting the USB device.

Unlike standard RS-232 serial connections that use separate Transmit (TX) and Receive (RX) lines, the CI-V bus merges TX and RX onto a single line.

If you are drawing your own top-level schematic in KiCad: icom ci v usb interface schematic top

The story of the is one of elegant simplicity in the face of complex technology. While other manufacturers often reinvented the wheel with every new radio, Icom’s standard has remained remarkably consistent since its introduction in the late 1980s. The Birth of a Standard

is the most common choice as it handles all USB-to-serial conversion. The "Combining" Diode

The simplest way to interface a standard USB-to-TTL module (which has separate TX and RX pins) with the single-wire CI-V bus is to bridge the signals.

: Modern schematics center around a bridge IC, most commonly the or the Silicon Labs CP2102 Go to product viewer dialog for this item. The TXD pin connects through a 1kΩ current-limiting

With the schematic understood, building the interface is straightforward.

If your interface drops its connection whenever you transmit high power on HF, wrap the USB cable around a Type 31 or Type 43 ferrite toroid right next to the interface box to choke out stray common-mode RF.

A direct connection uses a simple USB-to-TTL serial adapter directly connected to the radio. While cheap, this creates a direct electrical path between your computer’s switching power supply and your sensitive HF transceiver. This often introduces significant USB ground loop noise (RFI) into your receiver and risks damaging equipment if a voltage differential occurs.

~40×20 mm (e.g., similar to a CP2102 breakout) As explained above, the CI-V bus uses TTL

Unlike standard RS-232 serial interfaces that use separate Transmit (TX) and Receive (RX) lines, . The Connector: A standard 3.5mm mono phone jack.

Integrating an Icom transceiver with a computer opens up a world of automated logging, digital modes, and software-defined control. Icom uses a proprietary control system called the Computer Interface 5 (CI-V). While commercial USB-to-CI-V cables are widely available, building your own interface is a rewarding, low-cost project that provides excellent isolation and protection for your radio.

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.

: Since CI-V is a single-wire bus, you must connect the TXD and RXD pins of your USB chip together. A common method is connecting the RXD pin directly to the CI-V bus and using a 1N4148 diode