: High-reliability designs often use a 7417 hex buffer IC as recommended in the ARRL Handbook to isolate the computer from the radio. Implementation Tips
If you are building one from scratch today, is highly recommended.
Below is the complete schematic of a well-regarded USB CI-V interface design. The circuit uses a USB-to-TTL serial adapter, a few transistors, and some passive components, drawing all the power it needs directly from the USB port.
CI-V operates on standard TTL logic levels (0V to 5V). icom ci v usb interface schematic top
Option B: The High-Performance Optoisolated Circuit (Top Recommendation)
Once the hardware is assembled, you must tell the radio and the software how to talk to each other:
There is between the computer's ground and the radio's ground, protecting your radio's delicate microprocessor from power surges. 3. The Legacy Option: Transistor-Based CI-V Interface : High-reliability designs often use a 7417 hex
Figure 2: Detailed Schematic for the CI-V Level Shifter
Here are the most popular and reliable schematic approaches for building your own interface. A. The Classic Transistor Interface (Simple & Cheap)
PC SIDE (USB Power) | RADIO SIDE (CI-V Bus Powered) | TXD ---> [ 470 Ohm ] --->|----+ +---[ 1k Ohm Pull-up ] ---> To Radio 5V* LED | | (Optional if radio lacks pull-up) | | |/ GND (USB) ----------------+ | --| Phototransistor | |\> | +-------------------------> To 3.5mm TIP | | +-------------------------> To 3.5mm TIP | |/ RXD <-------------------------+----| Phototransistor | |\> USB 5V ---> [ 4.7k Pull-up ] | | | +--->|--------------------> To 3.5mm SLEEVE | LED | | | +---[ 470 Ohm ]------> To 3.5mm TIP The circuit uses a USB-to-TTL serial adapter, a
Extremely reliable, directly connects to USB, self-powered from USB. Design Note: Use a 2N7000 FET or 2N3904 for the inverter. C. Opto-Isolated Interface (Maximum Protection)
: Use a 3.5mm mono jack . The combined TX/RX signal goes to the Tip , and the module's GND goes to the Sleeve . Key Build Tips
This circuit diagram breaks down the components inside the "CI-V Level Shift" block. It is a bi-directional level converter and bus interface.