This approach is widely used in homebrew designs. Because the CI-V bus is a single wire where transmit and receive happen on the same line, you cannot simply tie your USB adapter’s TX and RX pins together—the driver stages will fight each other. The schematic must include a way to combine these signals.
Run a jumper wire from that same pin to the 3.5mm jack Tip .
CAT (Computer Aided Transceiver) is a generic term for computer control of a radio. CI‑V is Icom's specific implementation of a CAT system. Other manufacturers (Yaesu, Kenwood, etc.) use their own protocols, although many modern radios from all brands have similar physical‑layer characteristics. icom ci v usb interface schematic top
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Once construction is finished, it is time to test the interface. This approach is widely used in homebrew designs
Every seasoned builder has a story about following a schematic exactly and having the interface not work. The reason usually lies in the —the things that are not drawn on the diagram. Here are the most common silent pitfalls:
If using an isolator, draw a physical keep-out zone across all layers of the PCB beneath the isolation IC. No copper traces, ground planes, or vias should cross this line. Aim for at least an 8mm clearance gap. Run a jumper wire from that same pin to the 3
However, a computer's modern USB port speaks neither TTL voltages nor the CI-V bus logic. Its signals are digital, and the USB hardware expects to talk to something like a virtual serial port. For CI-V to work, we need an interface that does three things:
Note: This method is largely obsolete due to the cheap availability of direct USB-to-TTL modules, but it remains an excellent choice for scavenging parts from an older junk box. Bill of Materials (BOM) for the Top FTDI/CH340 Design
Controlling your Icom radio from a computer opens up a world of automated logging, digital modes (FT8, JS8Call), and seamless software-defined control. Icom uses a proprietary communication protocol called .
Match your radio's internal CI-V settings (typically 9600 or 19200 baud for older rigs, or Auto for modern rigs).