Icom appears to delight in charging outrageous prices for all transceiver accessories, so many Hams improvise instead. A few circuits have been published for CI-V interfaces, most of which use the MAX232 IC. Here is a very simple CI-V interface, originally described by OK2WY . I’ve made small changes to the modem control signals connections. Although the circuit doesn’t conform exactly to the RS-232 specification, it does work well and has the advantage of being easily constructed inside a 9 pin D-type shell. Please note that the resistor value 4K7 means 4700 ohms. The transistor types are not critical, I just happen to have plenty of 2N2222As.
I’ve used this interface on various PC’s and also Dell Latitude Notebooks with both an IC735 and IC706MkIIG. No problems have been experienced even at 19200 baud with the IC706. It has also worked successfully when using a USB/Serial adapter from a notebook. If a PTT function is required from the COM port, pin 7 (RTS) can be used to provide this facility.
The circuit is powered by DTR (pin4). I experienced some problems with YPLog using this power source. If YPLog is configured to use PTT from either the Parallel port or a different serial port from the one used by the CI-V Interface, the program drops the DTR signal, resulting in no power to the interface. This is easily resolved by powering the circuit from RTS (pin 7) instead of DTR (pin4).
I have also used this interface to program my Yaesu FT50R. Only a change of connector to a 4 pole minijack plug was required. Probably the interface can be used with other HTs, although I have not tried it.
Document originallly found at http://www.iv3sbe.webfundis.net/html/Cat.htm