Icom Ci V Usb Interface Schematic Top < 100% TRUSTED >

This document explains how to build a USB-to-Icom CI-V interface (PC ↔ Icom radio control bus), gives a recommended schematic, component values, wiring notes, and safety/EMC tips.

CI-V requires an open-collector driver.

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.”

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. icom ci v usb interface schematic top

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

, 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. This document explains how to build a USB-to-Icom

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

The term "schematic top" often refers to the high-level hierarchical view. Here is the functional breakdown of a standard CI-V USB interface: Before building or purchasing an interface, compare the

[USB Port] → [USB-to-UART bridge] → [Opto-isolation stage (TX direction)] → [Buffer/Driver] → [CI-V connector (3.5mm TRS)]
                                                    ↑
[CI-V connector] → [Signal conditioning] → [Opto-isolation stage (RX direction)] → [UART RX]

Most DIY designs use two optocouplers (typically 6N137 or PC900 for speed, or 4N35 for lower baud rates) to decouple the radio ground from the computer ground.

Below is a functional block diagram of the classic, proven “top-level” CI-V USB interface. Hundreds of online projects and commercial products (like the CT-17 or U5 Linker) follow this design.

       +---------------------+
       |   USB Connector     |
       +----------+----------+
                  |
       +----------v----------+
       |  USB-to-Serial IC   |
       |  (FT232RL / CH340)  |
       |  - TTL Out (TxD)    |---(0/3.3V)---+
       |  - TTL In (RxD)     |<--(0/3.3V)---+
       +----------+----------+              |
                  |                         |
       +----------v----------+              |
       |  Logic Inverter     |              |
       |  (Transistor/NAND)  |              |
       +----------+----------+              |
                  |                         |
       +----------v----------+              |
       |  Bidirectional      |              |
       |  Buffer / Open-     |              |
       |  Collector Driver   |<-------------+
       +----------+----------+
                  |
       +----------v----------+
       |  CI-V Connector     |
       |  (3.5mm stereo or   |
       |  2-pin phoenix)     |
       +---------------------+

Would you like a full component list, PCB layout example, or a specific IC’s connection diagram (e.g., FT232RL + 2N7000)?

When searching for "icom ci v usb interface schematic top", many users are trying to repair a non-working interface. Here’s how the top-level schematic helps diagnose faults:

| Symptom | Likely area (top-level block) | |-----------------------------|----------------------------------------------| | No control, but radio responds to CI-V commands from another device | USB-to-UART bridge (check drivers, TX/RX LEDs) | | Erratic control, especially on transmit | Lack of opto-isolation or ground loop | | Computer sees COM port, but no PTT or frequency readout | TX opto (IC2) or buffer transistor dead | | Stuck data (bus always low) | Open collector transistor shorted, or missing pull-up on CI-V line | | Interface works only at low baud rates | Optocoupler too slow (replace 4N35 with 6N137) |