Notes:
Before etching PCB or soldering on a protoboard, verify that your icom ci v usb interface schematic top includes:
The Icom CI-V USB interface is not a simple cable – it is a bidirectional, inverted, open-collector level converter. The top schematic presented here (USB serial chip → NPN inverter/open-collector → CI-V bus with pull-up) has become a de facto standard because:
Before building or purchasing an interface, compare the vendor’s schematic against this “top” design. If it lacks the open-collector NPN inverter stage on the transmit line (or uses a simple transistor without correct biasing), it will likely fail with Icom’s protocol.
For further reading, search for “Icom CI-V specification document” (Icom publishes the electrical spec) and open-source designs like “USB-CI-V by YO3FVR” or “W6IPA CI-V interface schematic.”
Building your own Icom CI-V (Communications Interface 5) USB interface is a popular DIY project for amateur radio operators. It allows you to control transceivers—from older models like the IC-735 to modern rigs—via a computer using a single 3.5mm mono cable. Understanding the CI-V Bus
The CI-V protocol is a bi-directional, single-wire TTL system. Unlike standard RS-232 serial communication which uses separate Transmit (TX) and Receive (RX) lines, CI-V combines them into one "DATA" line. Idle State: The line is held high (+5V TTL). Collision Detection: If the line is low, the bus is "busy".
Daisy Chaining: Multiple Icom devices can be connected in parallel; each is identified by a unique hex address. Core Schematic: USB-to-TTL (CI-V) icom ci v usb interface schematic top
To build a modern USB version, you need a USB-to-TTL serial converter (often based on the FTDI FT232RL or CP2102 chips). The "Two-Diode" or "Shorted" Method
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.
TX to DATA: Connect the TXD pin of your USB module to the Tip of a 3.5mm mono jack through a small signal diode (e.g., 1N4148) with the cathode facing the USB module. This prevents the TX pin from holding the bus high when it should be idle. RX to DATA: Connect the RXD pin directly to the same Tip. Ground: Connect the GND pin to the Sleeve of the mono jack. Buffered Open-Collector Schematic
For a more robust "top-tier" design that prevents data collisions and protects your radio, use an Open-Collector Buffer like the 7417 or 7407. Simple Icom CI-V Interface - QSL.net
CI-V (Computer Interface V) system is a standard protocol used by Icom transceivers for remote control. Because it uses an open-collector, half-duplex TTL-level signal, it requires an interface to convert these signals to levels a computer can understand, such as USB. Core Schematic Components A modern USB-to-CI-V interface typically revolves around a USB-to-Serial UART chip (like the FTDI FT232RL or Silabs CP2102). USB Bridge Chip : Converts USB data into TTL (0–5V) serial signals. Diode & Resistor Combination
: Since CI-V combines Transmit (TX) and Receive (RX) onto a single wire, a small circuit is needed to bridge the TX and RX pins of the UART chip. 3.5mm Mono Jack
: The standard physical connection for the radio end of the cable. Top Schematics & Design Options CI-V interface - Tučňák Wiki Tucnak - Nagano.cz Easy to make CI-V cable www.maniaradio.it Simple Icom CI-V Interface Yet Another ICOM CI-V Interface circuit | Next Electronics Next.gr Electronics Icom CI-V Interfaces and CT-17 Replacement – VK4AMG Notes: Before etching PCB or soldering on a
ICOM CI-V to RS232 interface diagram (using transistors, very small) ICOM CI-V Interface Seed Solutions CI-V interface - Tučňák Wiki Tucnak - Nagano.cz icom ci-v interface KA1MDA HOME PAGE
The Icom Communications Interface V (CI-V) is a proprietary serial communication bus used to remotely control Icom amateur radio equipment. While Icom sells the CT-17 level converter, you can easily build a high-performance USB CI-V interface using inexpensive USB-to-TTL modules. CI-V Technical Overview
The CI-V bus is an open-collector, bi-directional, single-wire system operating at TTL (5V) logic levels.
Idle State: The DATA line is held HIGH (+5V) by a pull-up resistor.
Active State: Devices communicate by pulling the line LOW (0V).
Connector: A standard 3.5mm mono jack. The tip carries the DATA signal, and the sleeve is GND. The "Top" Schematic: USB-to-TTL Method
The most efficient DIY design uses a common USB-to-Serial board (like those based on FTDI FT232RL , CP2102 The Icom CI-V USB interface is not a
, or CH340 chips). These modules provide separate TX (Transmit) and RX (Receive) pins, which must be combined into the single-wire CI-V bus. Simple Diode/Resistor Circuit
This is the most popular "top" schematic for its simplicity and reliability.
Join TX and RX: Connect the RX pin of the USB module directly to the CI-V Tip. Add a Diode: Connect the anode of a small signal diode (e.g., 1N4148
) to the CI-V Tip and the cathode to the TX pin of the USB module.
Purpose: This allows the TX pin to pull the bus low but prevents it from forcing the bus high, maintaining the open-collector requirement.
Pull-up Resistor: Connect a 4.7kΩ to 10kΩ resistor between the CI-V Tip and the 5V VCC pin on the USB module to ensure the bus idles high. Key Components List USB-to-TTL Module: FTDI FT232RL modules are highly recommended for driver stability. Diode: or similar high-speed switching diode. Resistor: 4.7kΩ (standard for CI-V). Plug: 3.5mm (1/8") Mono Phone Plug. Cable: Shielded audio cable to prevent RF interference. Software Setup
Once hardware is ready, you will need software to communicate with the rig. Popular choices include: Icom IC7300 A to Z #27 CI-V Settings
Creating a USB interface for the Icom CI-V, a protocol used by Icom radios for computer communication, involves designing a simple interface that converts the CI-V's serial signal to a USB signal that a computer can understand. The CI-V protocol uses a 9-pin D-sub connector with a specific pinout and typically operates at 9600 bps.
Below is a basic overview of how to create a USB interface for Icom devices using an FTDI chip, which is a popular choice for USB to serial conversions. This example assumes you are familiar with basic electronics and soldering.