A budget-friendly, compact alternative with excellent driver support.
+----------------+ +----------------+ +-------+ +---------------+ | | | | | | | | | USB Port +------+ USB-to-TTL +------+ CI-V +------+ Icom Radio | | (PC) | | Serial Adapter| | Level | | (CI-V Port) | | | | (e.g., FT232R)| | Shift | | | +----------------+ +-------+--------+ +---+---+ +-------+-------+ | | | | | | | +5V, GND, TX, RX | Data, GND | Data, GND | (TTL Levels) | | | | | +-----------------------+ | | v (Shared CI-V Bus) icom ci v usb interface schematic top
| Requirement | Why it matters | |-------------|----------------| | | CI-V is a shared bus; multiple devices can drive it low. A standard totem-pole output would short-circuit. | | Pull-up resistor (~4.7kΩ) | Ensures CI-V line idle high without current drain. | | Diode protection | Prevents CI-V voltage (5-12V accident) from back-driving FTDI chip. | | No ground loops | The interface should have opto-isolation (advanced) or at least common ground – but a direct ground is acceptable for single radio. | | Inversion as per Icom spec | Without correct inversion, commands will be byte-swapped or corrupt. | | | Pull-up resistor (~4
This is the most reliable, cleanest, and most popular design for modern ham shacks. It utilizes a dedicated USB-to-TTL breakout board (such as an FTDI FT232RL, CP2102, or CH340G) and a single switching diode to combine the lines. The Schematic Circuit: | | Inversion as per Icom spec |
There are three primary ways to design a DIY CI-V to USB interface. Below are the top schematics ranging from modern, streamlined chips to classic transistor designs.
Extremely reliable, directly connects to USB, self-powered from USB. Design Note: Use a 2N7000 FET or 2N3904 for the inverter. C. Opto-Isolated Interface (Maximum Protection)