The CI-V port is a 3.5mm mono jack that acts as a bidirectional, open-collector bus. TTL (0V to 5V or 3.3V). Wiring: Tip is Data, Sleeve is Ground.
Connect the RX pin of the USB module directly to the CI-V Tip . Add a Diode: Connect the anode of a small signal diode (e.g., 1N4148 Go to product viewer dialog for this item.
, or chips). These modules provide separate TX (Transmit) and RX (Receive) pins, which must be combined into the single-wire CI-V bus. Simple Diode/Resistor Circuit
Data from CI-V bus to PC RXD.
If you hear noise, you may need an optically isolated interface (like XGGCOMMS) to separate the PC ground from the radio ground. Conclusion
[ USB Breakout Board ] +---------------+ | GND |------------------------+---- (3.5mm Jack Sleeve / GND) | | | | TXD |-----[ 1N4148 Diode ]---+ | | |===>| | | RXD |------------------------+---- (3.5mm Jack Tip / CI-V Data) +---------------+ Use code with caution. How it works:
Would you like a , PCB layout example , or a specific IC’s connection diagram (e.g., FT232RL + 2N7000)? icom ci v usb interface schematic top
For those who prefer discrete builds, a simple two-transistor circuit can shift RS-232 levels (if using a serial-to-USB cable) or module levels to the CI-V bus.
The CI-V bus operates at standard standard 5V TTL logic levels.
I remember staring at the , a clean blueprint of logic in a world of messy RF. At the heart sat the FT232R chip , the silent translator converting USB’s frantic data into the steady, open-collector pulses the ICOM radio understood. To its left, a single 1N4148 diode stood guard—a simple gatekeeper ensuring the TX and RX lines played nice on the single-wire bus without talking over each other. The CI-V port is a 3
Connect the anode of the diode to the RXD pin using a small piece of hookup wire.
Before examining the schematic, it’s critical to understand the CI-V electrical interface. Unlike RS-232, CI-V uses:
Plug the USB interface into your computer. Windows 10/11 or modern Linux distributions should automatically download the FTDI or Silicon Labs drivers. Connect the RX pin of the USB module
This is considered one of the most reliable DIY schematics. The FTDI FT232RL IC handles the conversion from USB to UART levels perfectly. FTDI FT232RL IC 2× 1N4148 Diodes 4.7kΩ Resistor 3.5mm Jack
The Ultimate Guide to Building an Icom CI-V USB Interface: Top Schematics and DIY Guide