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: The simplest schematic involves connecting the RX line directly to the CI-V data line and connecting the TX line to the same data line through a small signal diode (like a ). This prevents the TX line from "fighting" the RX line. Buffer ICs : More robust designs use a buffer like the 7417 Hex Buffer icom ci v usb interface schematic top
| Pitfall | Consequence | | ------------------------------------------------------------ | ---------------------------------------------------------------- | | No open‑collector driver on the UART TX line | Weak signal, data corruption, or damage to the radio | | Ignoring the CI‑V bus pull‑up requirement | Unreliable communication, intermittent lock‑ups | | Selecting a USB‑to‑TTL adapter that does not supply 5 V on its I/O | Signals too low for the radio to recognise (especially with 3.3 V UARTs) | | Using the same baud rate for the radio and the software incorrectly | No communication or garbage data | | Forgetting that DTR (or RTS) might be needed for power in RS‑232 designs | Interface appears dead when connected to a USB‑to‑RS‑232 converter that does not generate ±12 V | This public link is valid for 7 days
CI‑V connector: Tip (data) ──┬─ 4.7k pull‑up to 5V or radio Vcc └─ drain of Q1 and 1k to RX Ring ──────── GND Sleeve ────── (optional +5V out) Can’t copy the link right now
Enable the internal pull-up or solder a physical between the RX pin and the board's VCC (5V) pin. 2. Eliminating RFI (Radio Frequency Interference)