Icom Ci V Usb Interface Schematic Top |top| May 2026

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:

Bill of Materials (Top-Level BOM)

| Component | Value / Part | Quantity | |--------------------|------------------------|----------| | UART bridge | FT232RL or CH340G | 1 | | Optocoupler (fast) | 6N137 or PC900 | 2 | | NPN transistor | 2N3904 / 2N2222 | 1 | | Resistor kit | 330Ω, 560Ω, 1k, 2.2k, 4.7k, 10k | each | | Capacitors | 0.1µF, 10µF (electrolytic) | few | | 3.5mm TRS jack | Stereo, PCB mount | 1 | | USB connector | USB-B or micro-USB | 1 | | Ferrite beads | 600Ω @ 100MHz | 2 | | 78L05 regulator | (if radio provides >5V) | 1 (opt) | icom ci v usb interface schematic top

Signal Flow:

  1. 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).

  2. 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).

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.

5. Understanding the Role of the “Top” Schematic in Troubleshooting

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: I couldn’t find a specific top-level schematic titled

| 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) |

Where to Find Verified Schematics