. These chips handle all USB protocol tasks and provide TTL-level Transmit (TX) and Receive (RX) signals.
: Solder the USB connector to the board and connect VCC and GND to the FTDI chip.
(e.g., 1N4148) is often placed between the TXD line and the CI-V bus to prevent the chip from "fighting" incoming signals when not transmitting. pull-up resistor
: Connect the interface to your radio and computer. Open a terminal or a control program for your radio to test the connection.
The TXD and RXD pins of the FTDI chip are connected together through a diode (1N4148) with the cathode facing the TXD pin. icom ci v usb interface schematic top
: Many schematics add a sub-circuit using the RTS (Ready to Send) or DTR (Data Terminal Ready) line from the serial converter to trigger a transistor (e.g., ) for PTT or CW keying. Connection Layout
: A budget-friendly, reliable alternative that uses FTDI chips. 4. Modern Approach: USB-Direct (No Interface Required) Modern Icom radios ( Go to product viewer dialog for this item. Go to product viewer dialog for this item. Go to product viewer dialog for this item. ) have . Schematic Requirement: A standard USB A-to-B cable.
Many cheap interfaces omit the inversion on TxD and just swap RX/TX – this fails with Icom because the protocol expects the idle state inversion.
If you have decided to build your own interface, following a set of methodical steps will save you hours of debugging. The TXD and RXD pins of the FTDI
Unlike standard RS-232 serial interfaces that use separate Transmit (TX) and Receive (RX) lines, . The Connector: A standard 3.5mm mono phone jack.
When the phototransistor conducts, it pulls the CI-V bus down to ground, replicating the serial start/stop bits. 2. Receive Path (Radio to PC)
: Typically, it uses a 3.5mm mono phone jack. The tip carries the data signal, and the sleeve is ground. 2. Standard USB to CI-V Schematic (FT232RL Based)
The FTDI-based schematic requires FTDI VCP Drivers to be installed on the PC. 5. Troubleshooting the CI-V Interface No Communication: Swap TX and RX wires. and the sleeve is ground. 2.
The connection to the radio's Tip is made from this junction.
This comprehensive guide details how to build a high-performance, electrically isolated USB CI-V interface. It covers everything from schematic design to physical PCB layout configuration. 1. Understanding the Icom CI-V Protocol
Building a DIY Icom CI-V USB interface is a popular project for amateur radio operators looking to avoid the high cost of official cables like the Icom CT-17
: For those using a basic USB-to-TTL adapter, a simple circuit using two transistors can combine the TX and RX lines into the single-wire CI-V bus.