Icom Ci V Usb Interface Schematic Top -

Most interfaces are bus-powered from USB.

Alternatively, a separate isolated DC-DC converter (e.g., B0505S) can generate a floating 5V for the radio side, eliminating the need to draw power from the radio.

Best for: Beginners and those who want a reliable, compact build inside a USB cable or small box. Common Chips: FTDI FT232RL, CH340G, CP2102.

This is the most popular method today because these chips output the exact TTL voltage (approx 5V or 3.3V) that the Icom radio expects. You do not need a MAX232 chip here. icom ci v usb interface schematic top

The Schematic Logic:

The Critical Component: A Diode is Required Because CI-V is a "half-duplex" single-wire system (the radio and the computer take turns talking on the same wire), you cannot simply tie the TX and RX pins directly together without risk of contention. However, with FTDI chips, there is a trick:

Schematic Parts List (FTDI Method):

Notes:

A direct USB-to-serial chip (like FT232 or CH340) outputs 0–5V/3.3V logic (TTL). The Icom CI-V bus operates at:

Thus, a simple USB-TTL cable will not work. You need a circuit that performs: Most interfaces are bus-powered from USB

If you prefer a ready-made product, several commercial interfaces appear at the top of search results, including:

However, building from a top-quality schematic gives you complete control over isolation quality, component choice, and cost (under $15).