, which bridges the computer's USB port to the radio's single-wire TTL bus. Core Schematic Components : Modern designs often use the or Go to product viewer dialog for this item.
Modern laptops lack RS‑232 ports, so a USB‑native interface is the most practical choice today. This approach uses a (such as the Silicon Labs CP210x series or an FTDI FT232R) to generate TTL‑level signals directly.
The TXD pin on the FTDI chip connects through a diode to the shared CI-V line. The RXD pin connects to the same line, allowing for bidirectional communication. A 4.7kΩ resistor acts as a pull-up to ensure stable 5V TTL levels [N5DUX].
Using an FT232RL requires soldering an SSOP-28 package. Use fine solder wire, plenty of flux, and a clean chisel tip iron to prevent bridging between the pins. icom ci v usb interface schematic top
Integrating an Icom transceiver with a modern computer requires a CI-V (Computer Interface Five) adapter. Most modern laptops and desktops lack native RS-232 serial ports, making a USB-to-CI-V interface essential for digital modes, logging software, and remote rig control.
The ICOM CI-V USB interface has numerous applications in amateur radio, including:
In this design, a USB-to-UART bridge chip (like the FTDI FT232RL, CP2102, or CH340E) replaces the traditional RS-232 transceiver. The schematic shows the bridge chip's TX and RX pins connected directly to the custom bus driver circuit, eliminating the need for an extra RS-232 level shipper. This is the most modern and efficient design. , which bridges the computer's USB port to
If using an isolator, draw a physical keep-out zone across all layers of the PCB beneath the isolation IC. No copper traces, ground planes, or vias should cross this line. Aim for at least an 8mm clearance gap.
Connect all radio-side grounds together: , Pin 5 of IC 2, and Pin 5 of IC 3. Configuration and Software Setup
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: This approach uses a (such as the Silicon
This is the minimalist's dream. The schematic often uses two general-purpose NPN transistors, such as or 2N3904 , along with a few resistors and diodes. It works by using one transistor to drive the bus when transmitting, and another to buffer the received data. This circuit is simple, low-cost, and effective for a single radio. However, it may not have the current sinking capability to drive a bus with multiple devices.
Connect the collector of the TX optocoupler's output transistor directly to the CI-V signal line. Connect a high-speed switching diode (such as a 1N4148) between the TX line and the input of the RX optocoupler. How it works: