The Icom CI-V system is a serial communication protocol used to control Icom radios. It uses a simple two-wire interface (Data and Ground) that operates at TTL logic levels (5V).
Modern computers no longer have serial ports (RS-232), and CI-V is not directly compatible with USB. Therefore, an interface is required to bridge the gap. The schematic design depends entirely on which USB chip you choose to use.
Here are the three most common schematic topologies, ranging from the easiest to build to the most traditional.
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.”
I couldn’t find a specific top-level schematic titled exactly “ICOM CI-V USB Interface Schematic Top” in public databases. However, the CI-V (Computer Interface V) is ICOM’s proprietary control bus for radios (e.g., IC-703, IC-706, IC-718, IC-7300, etc.). A typical USB-to-CI-V interface uses a USB-to-serial bridge chip (FT232RL, CP2102, CH340) combined with a level converter (since CI-V is TTL-level, not RS-232).
Here’s a useful reference schematic (top-level) derived from common amateur radio designs:
Before etching PCB or soldering on a protoboard, verify that your icom ci v usb interface schematic top includes:
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 uses inverted, open‑collector logic (one‑wire bidirectional data).
The USB side (UART) is standard TTL (non‑inverted). So you need:
Simplest working schematic (top‑side parts):
USB‑UART IC (CP2102) TX pin ──┬─ 10k resistor to 3.3V └─ gate of 2N7002 (Q1) RX pin ──────────┬─ 1k resistor ── drain of Q1 ──┬─ to CI‑V data line └─ (optional 2nd transistor for correct idle polarity)
CI‑V connector:
Tip (data) ──┬─ 4.7k pull‑up to 5V or radio Vcc
└─ drain of Q1 and 1k to RX
Ring ──────── GND
Sleeve ────── (optional +5V out)
Best for: Builders using older laptops with serial ports or standard RS-232 to USB adapters. Common Chips: MAX232, MAX233.
This was the standard design in the 1990s and 2000s. It converts USB to RS-232 voltages (+/- 12V), and then converts that back down to TTL for the radio.
The Schematic Stages:
If you prefer a ready-made product, several commercial interfaces appear at the top of search results, including:
However, building from a top-quality schematic gives you complete control over isolation quality, component choice, and cost (under $15).
The Icom CI-V system is a serial communication protocol used to control Icom radios. It uses a simple two-wire interface (Data and Ground) that operates at TTL logic levels (5V).
Modern computers no longer have serial ports (RS-232), and CI-V is not directly compatible with USB. Therefore, an interface is required to bridge the gap. The schematic design depends entirely on which USB chip you choose to use.
Here are the three most common schematic topologies, ranging from the easiest to build to the most traditional.
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. icom ci v usb interface schematic top
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.”
I couldn’t find a specific top-level schematic titled exactly “ICOM CI-V USB Interface Schematic Top” in public databases. However, the CI-V (Computer Interface V) is ICOM’s proprietary control bus for radios (e.g., IC-703, IC-706, IC-718, IC-7300, etc.). A typical USB-to-CI-V interface uses a USB-to-serial bridge chip (FT232RL, CP2102, CH340) combined with a level converter (since CI-V is TTL-level, not RS-232).
Here’s a useful reference schematic (top-level) derived from common amateur radio designs:
Before etching PCB or soldering on a protoboard, verify that your icom ci v usb interface schematic top includes: The Icom CI-V system is a serial communication
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 uses inverted, open‑collector logic (one‑wire bidirectional data).
The USB side (UART) is standard TTL (non‑inverted). So you need:
Simplest working schematic (top‑side parts):
USB‑UART IC (CP2102) TX pin ──┬─ 10k resistor to 3.3V └─ gate of 2N7002 (Q1) RX pin ──────────┬─ 1k resistor ── drain of Q1 ──┬─ to CI‑V data line └─ (optional 2nd transistor for correct idle polarity)
CI‑V connector:The Icom CI-V USB interface is not a
Tip (data) ──┬─ 4.7k pull‑up to 5V or radio Vcc
└─ drain of Q1 and 1k to RX
Ring ──────── GND
Sleeve ────── (optional +5V out)
Best for: Builders using older laptops with serial ports or standard RS-232 to USB adapters. Common Chips: MAX232, MAX233.
This was the standard design in the 1990s and 2000s. It converts USB to RS-232 voltages (+/- 12V), and then converts that back down to TTL for the radio.
The Schematic Stages:
If you prefer a ready-made product, several commercial interfaces appear at the top of search results, including:
However, building from a top-quality schematic gives you complete control over isolation quality, component choice, and cost (under $15).