The protocol operates at standard 5V Transistor-Transistor Logic (TTL) levels.
When the USB TXD pin goes Low (Logic 0), the diode conducts, pulling the CI-V bus Low.
Ensure the hex address in the software matches your radio's specific CI-V address (found in the radio's internal menu). icom ci v usb interface schematic top
A Japanese amateur radio operator, JI3XOK, published a design where he bought a semi-finished USB-COM adapter (using the CH340E chip) and added an opto-isolation circuit using a phototransistor and a simple low-pass filter (LPF) on the radio side to mitigate RF noise and ground loops. The schematic for this uses a few transistors in an emitter-follower configuration to drive the opto-isolator. This is an excellent design choice for those in high-RF environments or using inefficient antennas.
: 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 A Japanese amateur radio operator, JI3XOK, published a
The computer sees the interface as a standard virtual COM port.
For a reliable "top-tier" homebrew design, using a dedicated USB-to-TTL serial chip like the is highly recommended. ICOM CI-V - K7MEM : The standard physical connection for the radio
If you tell me which Icom radio model you are using (e.g., IC-7300, IC-7000), I can provide the exact pinout and recommended interface configuration .
Before diving into the hardware, it's essential to understand what makes the CI-V bus tick. Icom designed CI-V as a simple, yet robust, serial communication system.