Galvanic isolated CATaudio interface
for amateur radio
SM4XIU
Dec 10, 2004
Surely this homebrew will be stolen and copied tocomercial surface-mounted gear, cause this is not buyable anywhere (yet). But for those that want to homebrew a hi-performance interface with discrete components without paying $100 for it: This is it and it’s free, as amateur radio should be.
Background
This interface is brought to life because i wanted a cheap, hi-speed, fully galvanic isolated interface with both audio and CAT on the same board.
Isolated CAT-interfaces ther is, but none that can handle speeds up to 56700bps. Not for resonable amount of money anyway.
In the testbench 9600bps was the maximum when using ordinary opto-couplers and that was not good enough when running softwares like Ham Radio Deluxe Simon Brown, HB9DRV).So I made this homebrew to matchmy wishes.
What is it?
This homebrew is a level-converter interface,suitable for remote controling Icom, Yeasu, Kenwoodand other brands of amateur radio’s, from an ordinary PC.It also have audio transformers for the audio path.
It uses hi-speed optocouplers for the serial transmission and hardwareRTS/DTR-driven PTT-switch with an extra help-transistor to realy put the PTT-line to 0 volts.
This interface has all rules regarding groundings solved. It’s totaly galvanic isolated up to 2kV.
Power requirements
The RS232 logic and PTT logic drains the PC serial port with 10-15mA. If the serial port can’t supply that much (mainly some poor designed USB adapters), this interface can’t be used on that computer.
7-15v 15-30mA is also used from the rig or a wallmart. If you don’t use the LED’s it will consume less then 10mA.
The design
The board uses a MAX232 serial driver/converter, to get real RS232-levels,in conjunction with two hi-speed opto-couplers/drivers(6N137).
Hardware PTT is also included and isolated trough an standard opto-coupler and a help transistor to force the PTT-line to true 0 volts.
The audio-path goes through standard 600 Ohm audio transformes. VOX and CW-keying is NOT implemented.
Features:
- Totaly galvanic isolated, with 3 ground-zones (PC serial I/O ground, rigground and PC audio ground), accomplished by opto-couplers and transformers.
- The interface is powered from the computer serial port (10-20mA) and a separate 6-15v (10-30mA) feed from the rig or a wallmart.
- A flexible approach is made for connecting to computer/rig. A single 3,5mm stereoplug for PC audio, 9 pin D-sub for serial data to the PC and a Mini-DIN6 (PS/2 mouse style) connector for the rig. “Not connected holes”for soldering extra connection-cables in the box is also avalible on the board to use as you like.
- Simple construction with well known components and no SMD´s, in a “anyone can build this”-design.
- 50x110 mm PCB size.
- Components costs about $15-20 and a lot of it can be found in the junk box.
Assembling the interface
It’s made for “garage manufacture” so praticly anyone can make the etching of the board at home. The PCB is a single layer board with trackwidth 1,5-2 mm, so even poor etching would make a working result.
JP1 (beside the DB9 connector) determines DTR or RTS for PTT. Usually RTS is used for PTT(junper closest to the LED´s).
The RS232 port is a normal DTE. A straight cable (modem cable) should be used to connect the interface to the PC.
DIN6 (CON3) rig connector pinouton the interface:
- RX CAT
- TX CAT (connects to pin 1 for Icom)
- PTT
- Speaker or line out from the rig
- VCC (6-15v)
- Rig mic or line in to the rig
Ground in the shield.
Phono 3,5mm configuration:
Tip PC mic or line in
Ring PC speaker or line out
Barrel. PC soundcard ground
Components
Remember that if both the rig and PC is connected to the the same ground (protective ground), this interface don’t helpfrom ground loops.But it will not blow up anything if you get a total ground-failure as other interfaces would do.
Components
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C11uF 16v
C21uF 16v
C31nF
C41nF
C51uF 16v
C61uF 16v
C71nF
C81uF 16v
C910uF 16v
C101uF 16v
CON13,5mm Phono female
CON2DIN6 female
CON3Dsub9 female
D11N4148
D21N4148
JP13-pin jumper
LED1Red 3mm
LED2Green 3mm
R1470
R2560
R3220
R410K
R5680
R61K
R7560
R810K
R93K3
R10680
R11560
R12220
T1BC557
T2BC547
Tr1600Ohm 1:1
Tr2600 Ohm 1:1
U16N137
U26N137
U3PC817
U4MAX232A
VR11k
VR21k
Z15v1
Z25v1
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Capacitors with voltage rating is electrolytic and the voltage rating is the lowest rate that should be used.
Late changes that’s not corrected on the PCB drawing: C3,C4 and C7 are all 1nF.
And for those American friends that don’t understand what 3K3 is, I hereby translate it to 3.3k .
Some cablesand plugs is also needed. See the next two pages!
Making theconnecting cables
Rig cable
The interface connector to the rig is a standard mini-DIN 6 connector. It’s the same connactor computer uses to the mouse and keyboards (PS/2-style).
You also need the connector(s) to your ACC-socket and if it’s a specific plug for CAT-socket on the rig.
The TNC-port on moust rigs don’t supply any power, so in these examples I have not mentioned that type of port. If used you need to supply 6-15v from elsewhere.
Tip!
It can be a good idea to, already from the beginning, put ferites on the cable before soldering. It may be needed in the future when HF is hitting the cable and makes the interface go nuts. Normaly it’s good enough to put ferites on therig-cable only.
Please, note that the Mini-DIN connector is NOTdirectly compatible with the TNC-port found on some rigs.You can’t use a straight cable!
CAT interface connector (female)Icom 13 pinIcom dual 8+7pin version
ICOM with 13-pin ACC socket
CAT-InterfaceRig
1 CAT RXShorted with CAT-pin 2 and connected to tip in the 3,5mm phono plug.
2 CAT TXShorted with CAT-pin 1 and connected to tip in the 3,5mm phono plug.
3 PTTpin 3 (orange) and pin 7 (purple), HSEND/VSEND
4 to PC audiopin 12 (light blue), AF
5 Powerpin 8 (gray), 13,8V
6 from PC audiopin 11(pink), MOD
Shieldpin 2 (red), GND (GND is not needed in the CAT phono plug)
ICOM with 2 ACC sockets (8+7 pin)
CAT-interfaceRig
1 CAT RXShorted with CAT-pin 2 and connected to tip in the 3,5mm phono plug.
2 CAT TXShorted with CAT-pin 1 and connected to tip in the 3,5mm phono plug.
3 PTTACC2 pin 3 and 6, HSEND/VSEND
4 to PC audioACC1 pin 5, AF
5 PowerACC1 pin 7, 13,8V
6 from PC audioACC1 pin 4, MOD
ShieldACC2 pin 2, GND (GND is not needed in the CAT phono plug)
Yaesu/Kenwood
There are so many different plugs so I don’t even try to make the connection tables.
Cables is made in the same manner but CAT RX/TX are not shorted together on these rigs. Look in you owners manual of the rig for more information and look at the Icom-examples above.
The PC audio cable
Buy a stereo 3,5mm phono to 2xRCA audio-cable in suitable length. (It should go between the PC and the interface.) Also buy two stereo phono plugs for soldering.
The cable need some “attention”. Cut away the red RCA-plug and solder the first extra phono plug to it. The center lead should go to both the tip and ring, shield to barrel. Mark this one red.
Cut away the other black (or white) RCA connector and solder the other phono plug to it in the same way as the first.
The red one should connect to the PC soundcard mic or line in port and the other to speaker out or line out. Usually the soldering is the same on the black RCA lead (speaker/line-out plug) but if you experience problems, try to single-feed the tip or ring.
Junkbox map
Below is some suggestions where to look for needed stuff in the junk-box.
Old thunder-”bited” modems include:
One audio-transformer
DB9 female serial connector
Serial cable, DB9 female – DB9 male
3,5mm Phono-socket
LED’s
Old motherboards from computers:
Single mini-DIN 6 (PS/2) sockets for PCB-mount(from old Compaq, IBM and HP etc)
Jumper pins and jumpers
Audio transformers could also be bought from Radio Schack or as a ”Ground loop isolator” in any
car-audioshop.
Build and use this interface at own risk! Iwill not take responcibility for any fault this interface may do. I run it 100% sucessfully on my IC-706mk2G, IC-718 and others.
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Component placement with tracks
Components placement and dimentions
PCB, mirrored for best copy to film (and PCB)
Schematic
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