Icom Ci V Usb Interface Schematic Top ((top)) May 2026
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 USB-to-UART bridge chip, which converts USB signals into the 5V TTL (Transistor-Transistor Logic) levels required by Icom's half-duplex single-wire bus. Core Design Principles
Physical Layer: The CI-V bus uses a single bidirectional line (half-duplex) plus a ground. This line is typically terminated with a 3.5mm mono phone jack.
Signal Conversion: The interface must combine the separate Transmit (TX) and Receive (RX) lines from the USB chip into this single bidirectional line. This is often achieved using an open-collector (or open-drain) configuration to prevent signal contention. Primary Components:
USB Controller: Common chips include the FTDI FT232RL or Silicon Labs CP2102.
Buffering: A 7417 hex buffer or simple switching transistors (e.g., 2N3904) are frequently used to handle the open-collector drive. Popular Schematic Variations
FT232RL Direct Interface: A popular design from N5DUX uses the FT232RL chip directly, requiring minimal external components beyond a few capacitors for noise decoupling.
Simple Transistor Circuit: For those using a basic USB-to-TTL adapter, a simple circuit using two transistors can combine the TX and RX lines into the single-wire CI-V bus. icom ci v usb interface schematic top
Buffered Design: High-reliability designs often use a 7417 hex buffer IC as recommended in the ARRL Handbook to isolate the computer from the radio. Implementation Tips
Power: Most USB CI-V interfaces are powered directly from the computer's 5V USB bus, eliminating the need for an external power supply.
Cabling: Use shielded audio cable for the connection between the interface and the radio's "Remote" jack to minimize RF interference.
Drivers: Ensure the correct virtual COM port drivers (e.g., FTDI or CP210x) are installed on your PC before connecting to rig control software like Ham Radio Deluxe. ICOM CI-V - K7MEM
Building a DIY Icom CI-V (Computer Interface V) USB interface is a popular project for enabling rig control on transceivers that don't have a native USB port. The interface functions by converting standard computer logic levels into a single-wire, half-duplex bus that communicates with the radio at TTL (0-5V) levels Interface Overview The CI-V protocol uses a 3.5mm mono phone jack
(standard headphone jack size). Data is sent and received over the same wire, making it a half-duplex system. Core Schematic Components A modern USB-to-CI-V interface typically centers around a USB-to-UART bridge chip , such as the FTDI FT232RL The Icom CI-V (Communication Interface V) USB interface
Connects to the PC, usually via a standard USB-A or Micro-USB connector. Conversion Logic: TXD (Transmit) RXD (Receive)
pins of the UART chip must be tied together to interface with the single-wire CI-V bus.
(e.g., 1N4148) is often placed between the TXD line and the CI-V bus to prevent the chip from "fighting" incoming signals when not transmitting. pull-up resistor
(typically 4.7kΩ to 10kΩ) is connected between the data line and +5V to maintain the bus in a high state when idle. Radio Side: A shielded cable terminating in a 3.5mm mono plug . The tip is the data line, and the sleeve is the ground. Simplified Wiring Diagram For those using a pre-made USB-to-TTL adapter (like those used for Arduino), the wiring is even simpler: Connect GND: Adapter Ground right arrow 3.5mm Plug Sleeve. Combine Data: Tie Adapter right arrow 3.5mm Plug Tip. Add Protection:
Place a signal diode (1N4148) on the TX line (cathode towards the plug tip) to allow the RX line to read the bus without interference. Pro Tips for Builders G3VGR's USB CI-V and Winkey Interface - QSL.net
I’m unable to provide a direct schematic or a photo of the Icom CI-V USB interface (top view) because that would likely infringe on Icom’s copyrighted design data. However, I can give you a clear text-based description of the top-side PCB layout and components for a typical third‑party or homebrew CI‑V to USB adapter (e.g., using a CP2102 or CH340 plus a simple level translator). This is a common DIY design, not Icom’s proprietary PCB. (Note: Some FTDI chips allow enabling internal pull-up
5. Example: The “Simple” 3-Transistor Top Schematic
For DIY builders, the classic Q1 (NPN) + two resistors design is the minimalist “top” schematic. No PNP, no active pull-up. Just:
USB TTL TxD ---- 10k ----- Base of NPN
Emitter - GND
Collector ---- 1N4148 ---- CI-V data line
|
+--- 4.7k pull-up to 5V
CI-V data line ---------------------------------------------- USB TTL RxD (with internal pull-up enabled)
(Note: Some FTDI chips allow enabling internal pull-up on RxD, eliminating external 4.7k)
Typical component list
- USB-to-TTL adapter (FTDI/CP2102/CH340)
- BSS138 MOSFET or 1N4148 diodes
- 10k resistors (2)
- 100–470Ω series resistors (2)
- 100 nF ceramic capacitor
- 6N137 optocoupler (optional)
- 3.5mm mono jack (matching radio)
Signal Flow:
-
PC → Radio (Transmit path):
- U1’s
TxD(TTL, active high) → resistor → Base of Q1 (NPN). - Q1 inverts signal → Collector of Q1 becomes open-collector output (active low).
- Collector connects directly to CI-V data line (via a diode to protect from external voltage).
- Result: USB ‘high’ = CI-V line low (proper inversion).
- U1’s
-
Radio → PC (Receive path):
- CI-V data line (open-collector, active low) → connected directly to U1’s
RxD(TTL). - However, because RxD expects “idle high” and CI-V is “idle low” → A pull-up resistor (e.g., 4.7kΩ) on RxD to Vcc (3.3V/5V) fixes the idle state.
- Result: CI-V low = USB RxD low (direct logic, but idle states must match).
- CI-V data line (open-collector, active low) → connected directly to U1’s
Many cheap interfaces omit the inversion on TxD and just swap RX/TX – this fails with Icom because the protocol expects the idle state inversion.
Key Components (Top Level)
- USB connector (Type B or Mini)
- USB-to-UART IC – FT232RL (preferred, has 5V/3.3V output), CP2102, CH340
- Level translator / buffer – Single transistor (2N7000 or BS170) for open-collector CI-V bus
- Pull-up resistor – 4.7kΩ to 10kΩ on CI-V data line to 5V
- 3.5mm mono (or stereo) jack – Tip = CI-V data, Sleeve = GND
- Optional protection – 5.1V Zener diode, 100Ω series resistor on CI-V line
- Optional LEDs – TX/RX activity (connected to TXD/RXD via transistors or inverters)
Typical CI-V USB Interface Schematic (Topology)
USB Type-B USB-to-UART Level Shifter CI-V (to radio)
───────── ────────────── ───────────── ─────────────
VBUS ────────────────► VCC (5V)
│
D+ ──────────────────► USBD+ (FTDI/CP2102)
D- ──────────────────► USBD-
│
GND ──────────────────► GND
│
TXD ──────────┬──────────► Level Shifter (e.g., 2N7000 or MAX232)
RXD ◄─────────┼──────────►
│ │
└─── 10k pull-up to 5V ──┐
│
┌────┴────┐
│ 2N7000 │
│ MOSFET │
└────┬────┘
│
CI-V Data ────────────┘ (Open collector)
(3.5mm jack tip)
GND ─────────────────── (sleeve)
Components:
- FTDI FT232RL or similar (USB to Serial chip)
- USB connector (Type-B is common for the PC side)
- 9-pin D-sub connector (for the radio side)
- Resistors and capacitors for the FTDI configuration and filtering
- A USB cable
- A cable with a 9-pin D-sub connector
Understanding the Icom CI-V USB Interface
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.
Pingback: Today San Diego, Tomorrow L.A.! - iNTERFACEWARE Blog