Sunday, October 9, 2011

The $10* Icom CI-V Computer Interface

The $10* Icom CI-V Computer Interface

For Computerized Rig Control or Logging

Utilizing No External Power and all parts from

DB9 Serial Port Connections

The DB9 serial port pin 2 is the RxD and is applied to the LTC1383 pin 14
The DB9 serial port pin 3 is the TxD and is applied to the LTC1383 pin 13
The DB9 serial port pin 5 is a common ground in the circuit
The DB9 serial port's DTR (pin 4) and RTS (pin 7) supply voltage to the input lead 1 of the 78L05 5 volt regulator. You should be able to measure +5 volts output between lead 3 (output) and lead 2 (ground) of the regulator (with a digital voltmeter!). Voltage is applied to pin 16 of the LTC1383.

Parts List

QTY Description RS part # Cost/Piece Total cost

1 Linear LTC1383 5v RS232 to TTL converter IC 900-6407 $5.63 $5.63
2 Ferrite Beads 900-5005 $0.25 $0.50
2 22 uf 16 volt electrolytic caps 900-7665 $0.15 $0.30
4 0.47 uf electrolytic capacitors 900-7674 $0.14 $0.56
2 1N5818 diodes 900-3178 $0.49 $0.98
2 1uH RF chokes 900-4954 $0.49 $0.98
1 100pf capacitor 900-2201 $0.16 $0.16
1 78L05 5 volt regulator 900-4491 $0.36 $0.36
1 DB9 Female Connector See text $0.00 $0.00
1 1/8" miniature phone plug 910-0755 $0.89 $0.89

* Not really $10 - but definitely about $20 when all is said and done. Parts shipping is extra, but got me the parts in 2 days since they shipped USPS Priority! Optional parts all from Radio Shack retail store: 16 pin DIP socket, aluminum case, metal standoffs, IC PC Board material (276-159B), grommets - all about $6 more. These parts can be ordered online if you are not near a store, but shipping on these parts took over a week when ordered online since they come UPS ground from a different warehouse apparently.

What rigs will this work with?

The answer is found in your manual. If the CT-17 is listed as an option, this circuit should work. Check the back of the rig - the CT-17 interface is usually labeled "REMOTE" and requires a 1/8 inch mono phone plug. These rigs should be OK: IC-761, 765, 706, 756, 775, 781, 746, 271, 471, 275, 475, 725, 726, 728, 735, 736, 737, 970, R71, R72, R700, R7000, R7100, and R9000. Some older Icoms like the 751a required a UX14 option since they were CI-IV and not CI-V. And some rigs with digital readout like the IC-701 lack the internal microprocessor to be able to be controlled by computer.

Do I Need to do anything to my rig to set it up?

Once again, read your manual. The software will want to know the rig's CI-V Address and its baud rate. For more modern transceivers, set the menus for "Transceive Mode", and "Auto" Baud Rate. For example, on my IC-746, the address is 56h and baud rate is set to Auto. I tried all software at rates up to the maximum of 19,200 baud and the 746 recognized them all. If your older radio has a fixed baud rate, be sure to set your software to match.

What Software Can I Use?

· IC-746 software (RS-746) looks so much like a real IC-746, it is scary! It can be found at:
---register for e-groups to download (if you don't mind looking at a 746 onscreen, you can even use this software to operate the IC-706 if you put in its CI-V Address). I don't believe that this software is "free", so contact Icom to register.
· Software for the IC-706, 706MkII, and 756 can be found at:
This software developed by this dedicated group of hams is FREE!
· TRX-Manager is from Laurent, F6DEX in France and offers a free (time/use limited) demo. It has the most features by far and does some logging too. Highly Recommended. Works with most Icom models:
YP Log Program (Logging with some feature/frequency control):

Where can I learn more about CI-V Codes and also how do I test my newly constructed interface?
As for programming the CI-V interface, Ekki DF4OR, is one of the worlds experts. He has a great site at

Lots of info and other CI-V interface circuits besides mine.
AA6YQ has developed excellent freeware called "CI-V Commander". You can verify that the LTC1383 is sending commands in both directions and that the circuit is wired correctly. In fact, anyone building the interface should try this software to verify that they built the interface properly and that their Icom's CI-V address, baudrate, etc. are set correctly:

It is also a great tool to learn about CI-V commands

Will this circuit help me do computer-based SSTV, RTTY, PSK31, ETC?
No. These modes require an interface to your soundcard, speaker and mic. See these references:
Soundcard Interfacing:

Can I hook up multiple Icom radios in parallel on the interface as with the original CT-17?

I'm not sure (untested as of yet). Each radio must have its own unique address (so if you were lucky enough to have two IC756Pros, one of them would have to have its default address changed in the setup menu). Also, one knowledgeable ham/engineer named Mario (Marijan Miletic, S56A, N1YU) has suggested a modification to my circuit to limit the current on the CI-V bus to 5 ma. He states that this will eliminate the possibility of software errors if multiple radios are connected in parallel. Here is a diagram of his suggestion. It will require 2 additional parts, so you might want to order these up front if you would like to try his suggestion:

Will this interface work with my Yaesu, Ten-Tec or Kenwood?

Some Ten-Tec's need a level converter just like the Icom's, so I have a feeling this circuit will work as-is. Yaesu splits their TTL lines into "serial in" and "serial out" - so you should be able to use separate leads from IC pins 11 and 12 (with their own chokes and 100pf caps to ground) as well as the ground connection. You would then use a 2 conductor shielded cable to the proper sized DIN plug for your model Yaesu. Pin 11 would go to "serial in", pin 12 to "serial out" and shield to ground on the Yaesu DIN plug. This has not been tested, so let me know how this works. The Kenwood is a bit more complex from what I hear. Many models use an IF10 interface in addition to a TTL/RS232 interface. You may be able to adapt my circuit to include a hex converter IC from pins 11 and 12 and power it from the same 5 volt source. Please let me know if you are successful.

Theory of Operation

The ICOM CT-17 RS232 computer level converter is both costly and requires external power. By using a cheap, readily available ultra low power TTL to RS232 converter IC, the Linear LTC1383, one can make a self-contained unit, which derives its power from the serial port itself. Although the IBM PC serial port was designed without a DC power pin, early mouse designers figured out a way to squeeze some low-current DC power from RTS or DTR lines (or from BOTH in the case of the design shown above). The LTC1383 draws only about 220uA at 5 volts - far less than most mouse circuitry. The above circuit should work with just about any serial port, including some otherwise finicky PC laptop ports. The LTC 1383 IC does all the work and requires only 4 capacitors to charge the internal pump circuits. Although one can use tiny 0.1uf non-polarized caps for the 4 charge caps, I chose some 0.47uf miniature polarized radial electrolytics to be extra sure of speedy response times in the heat of DX J . All parts are available at the time of this writing online from, but might be hard to find at the retail stores. I have no affiliation to Radio Shack, but enjoy their excellent website and variety of fairly cheap parts.

I chose to use some pre-punched general purpose DIP circuit board, a 16-pin DIP socket, 4 standoffs, 2 grommets and a tiny aluminum case to wire the circuit - which would add about $6 to the cost. Anal-retentive hams can etch and drill their own circuit boards! I'm sure some industrious hams will figure out a way to package the whole circuit inside a DB9 shell!

Instead of purchasing a DB9 female connector, I pilfered the connector and cable from an old broken Microsoft™ serial mouse. I not only got a "free" DB9 connector, but I found that the 4 conductor shielded cable used by the mouse already had my 5 connections made to the right pins! I even used a couple of feet of the same cable (after cutting off the 3 unused leads) as a single conductor shielded cable to run from the aluminum box to the 1/8 inch miniature phone plug for my IC-746. One builder found that he had a short in his mouse cable, so definitely test it thoroughly before using my mouse suggestion. If the thought of harming an innocent mouse is too hard to take, buy a db9 female and plastic or metal shell.

IMPORTANT: If you want to use a DB25 serial connector instead, remember that the ground pin is 7, DTR is pin 20, RTS is pin 4, TxD is pin 2 and RxD is pin 3! This would certainly give you more room in the casing to house the circuitry if you decide to go that route.

A note about the ferrite beads. Order two of part number 900-5005. I received 2 packs of 25 beads and wasted $0.25. But others have only received 2 beads and were happy that they ordered quantity "2"! So life is like a box of chocolates. You won't know what you get till you open the Radio Shack box.