The output transistor side connects to the FT232RL RXD pin with a 4.7k-ohm pull-up resistor to the USB +5V. 3. The Bi-Directional Bus Combiner (Radio Side)
The bus rests at a high state (5V) via a pull-up resistor. Devices communicate by pulling this line low (0V).
FTDI FT232RL or Silicon Labs CP2102. (A CH340G can also be used as a budget alternative).
I can provide specific pinouts for your radio model or adapt the schematic for your exact parts layout. Share public link
You must set CIV USB port to Link to [REMOTE] in the radio menu to allow software to control the radio. 5. Troubleshooting the CI-V Interface
Ground loops between a computer and a radio transceiver introduce significant RF noise, hum, and can potentially damage equipment during a lightning strike or power surge.
PC SIDE (USB POWERED) │ RADIO SIDE (RIG POWERED) │ ┌───────────────────────┐ │ ┌──────────────────────┐ │ │ │ │ │ │ USB-to-UART │ │ │ 3.5mm MONO JACK │ │ Bridge IC │ │ │ (To Radio) │ │ (FT232RL / CH340) │ │ │ │ │ │ │ │ ┌───┐ │ │ TXD ───[1kΩ]───┐ │ │ │ ┌────┤TIP│ CI-V Bus │ ▼ │ │ │ │ └───┘ │ │ ┌───┐ │ │ ┌─────┼──┘ │ │ │LED│ │ Optical │ │ │ ┌──────┐ │ │ └───┘ │ Coupling│ ┌─┴─┐ │ ┌────┤SLEEVE│ Ground│ │ │ │ ───► │ │Rx │ │ │ └──────┘ │ │ GND ───────────┴────┼──────────┼──┤PT ├─┐ │ │ │ │ │ │ └─┬─┘ │ │ │ │ │ │ │ └───┼─┼──┘ │ │ RXD ◄───────────────┼──────────┼────────┼─┼──┐ │ │ │ │ │ │ │ │ │ ┌─┴─┐ │ ┌─┴─┐│ │ │ │ │Rx │ │ │LED││ │ │ │ │PT ├────────┼◄── └───┘│ │ │ │ └─┬─┘ │ │ │ │ │ │ │ │ ├──┘ │ │ │ VCC (+5V) ──[10kΩ]──┴──────────┼────────┼─────┘ │ │ │ │ │ └───────────────────────┘ │ ▼ 1N4148 │ │ ─── │ │ │ │ │ ▼ │ Use code with caution. Detailed Wiring & Circuit Logic 1. Transmit Path (PC to Radio)
Consider a small buffer IC like the . The schematic would connect the USB bridge's TXD pin to an input of the buffer. The output of that buffer then connects to the CI-V bus (the tip of the 3.5mm plug) via a small current-limiting resistor. The RXD pin of the USB bridge connects to the same bus line through another buffer, but configured to listen. This isolation prevents transmission from feeding back into the receiver, creating a proper, professional-grade interface.