The simplest schematic—and often the first homebrew design that emerges when you look online—uses two NPN transistors (e.g., 2N2222A) and a handful of resistors and diodes. The signal flow works as follows:
: Solder the 1N4148 diode and 10k resistor between the TXD and RXD pins as specified in your chosen schematic to create the single-wire bus. Wire the 3.5mm Jack Connect the of the 3.5mm mono plug to the combined TXD/RXD line. Connect the to the GND pin of the USB module.
to convert USB signals into standard asynchronous serial UART signals (TX and RX). Level Shifting/Interface Logic icom ci v usb interface schematic top
This path carries data from PC TXD to the CI-V bus.
This schematic uses the highly stable (or a pre-assembled FTDI/CH340 breakout board) alongside a simple diode-steering network. Required Components The simplest schematic—and often the first homebrew design
Connect the TXD pin of your USB module to the Tip of a 3.5mm mono jack through a small signal diode (e.g., 1N4148) with the cathode facing the USB module. This prevents the TX pin from holding the bus high when it should be idle. RX to DATA: Connect the RXD pin directly to the same Tip . Ground: Connect the GND pin to the Sleeve of the mono jack. Buffered Open-Collector Schematic
CI-V requires an open-collector driver.
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.
Are you interested in adding to fully protect your PC from ground loops? Share public link Connect the to the GND pin of the USB module