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Author Topic: Interface PC and IC-730  (Read 5810 times)

Posts: 14

« on: July 21, 2001, 12:24:29 PM »

I am trying to interface my computer and IC-730 to key transmitter but the optocoupler will not create a dead short for keying the PTT in the transmitter. There is a little resistance accross the octocoupler that won't throw the transmitter fully keyed.

Any help?

Thanks in advance

Posts: 550


« Reply #1 on: July 21, 2001, 01:21:15 PM »


Opto-couplers are not linear devices so they are either ON or OFF. If it is not ON good enough, it may be defective. Make sure there is no resistance in-line with the T/R circuit... (Can you shortout the opto directly and make the T/R relay work?) Perhaps you can by-pass the opto device and use a more conventional single transistor circuit. You can find the circuits on the web or I can point you to

GL, Griff

Posts: 5

« Reply #2 on: September 09, 2001, 02:46:34 AM »

Hi Jerry -

   I set up my IC-730 on PSK-31 back in early July first using DigiPan, and then MixW v2.0.  It couldn't have been simpler:  Connect the audio from the IC-730's speaker to the computer sound card's (Sound Blaster Live!) line input (be sure to mute your line input so it won't play thru the speaker.  The next step tells you why:  don't create a feedback loop!);  Connect the sound card's speaker output to the mike receptacle's audio input pinout.

  Activate your VOX, and then audio at the mike input from the computer's transmit audio coming from the  soud card's speaker output will both key up the IC-730 and provide its transmit audio.  When you keystroke to stop transmitting the tone stops, the VOX lets go and you're back in the receive mode.  No interface, and a strict application of KISS (Keep It Simiple Stupid!).

  Works great and has gotta be the worst piece of news imaginable for the makers of buggy-whip TNCs, modems & interfaces.

             Here's the Nitty-Gritty
                  Making it work!

  Big problem, though:  You're gonna have to read your IC-730's schematic to figure out which pin of the mic receptacle is the audio in (pin 1. Gnd/common=7); and, you gotta (shudder - dare I say it in this day and age of plug & pray?) SOLDER! This is necessary to fabricate the cable that will connect the sound card's speaker output to the mike input.  Use a simple shielded mike cable, a duplicate of your IC-730 mike plug, and, of course, the proper connector to mate with your cound card's speaker output, whatever that might be.  That'll take care of the transmit audio.  The receive audio is a bit simpler:  If you're lucky enough to have a pre-made cable with the IC-730's speaker plug at one end and a phono connector at the other, you're pretty well there.  If your sound card's line input uses phono plug input, plug the phono plug into the left (white) channel.  You could get fancy and use a "Y" connector and feed your speaker audio into both left & right ... but, it isn't really necessary.  That's it - you're ready to go.

   If your computer is going to be dedicated strictly to PSK and radio work, follow these gain setting procedures (If not, you're on your own):
 1. Right click onto your speaker icon in the lower right quick start tray of your monitor screen and open up the volume controls.  
 2. Click onto "options" in the upper left corner of your screen, and then  "properties", and then click onto the "playback" radio button.  
 3. The safe thing to do at this point is check (mute) everything in sight, especially "line-in" to keep it from feeding into your speaker and then to your IC-730 mike. It still functions in mute; it just doesn't get to the speaker output.
 4. click onto the "recording" radio button and check everything there, too.  Then move directly down and check onto "OK".  You'll see a line of record volume controls, and your job here is to be sure that you've selected "line-in" for your audio input.  If you fail to do that, the IC-730 speaker output won't get to your computer's innards.  For starters, put your "line-in" setting at a notch and a half up from the bottom.
 5. Go back to the upper left corner of your screen and left click onto "options".  Left click onto the "Playback radio button", then move to the bottom and click onto "OK".  Now, you'll see the playback volume controls.
 6. It would be safe at this point to mute everything except the "wave" channel.  Your transmit audio is produced thru this channel, so don't mute it! Set the wave volume control about a notch down from the top.  Remember, the IC-730's mike is a pre-amplified device, so the audio input to the transceiver coming from the computer is going to have to be a little "stiffer" than you'd first think.  That's why the rather high wave setting.
 7. At this point, I usually minimize rather than exit from these volume controls.  You will have it ready to tweak it as you get into it.  One last thing - "Play Control", or overall speaker volume setting should fall somewhere around a notch below maximum.

  Those are the settings I use between the sound blaster live! and my IC-730.  I do it that way so the mike and speaker settings on the IC-730 remain the same as I use when I'm on SSB/voice.  You might have other ideas, have at it, and have fun!

   See you on 10, 15, or 20M PSK, Jerry - Join the fun!

Red Erickson, W2KWN/6

Posts: 3

« Reply #3 on: November 27, 2012, 02:00:46 PM »

The reason the opto will not key the IC-730 is because the PTT relay pulls almost 80 ma compared to 5 - 10 ma of most newer radios. The opto can't handle that much current. The fix is to put a darlington configured transistor after the opto to help it along. Any NPN transistor capable of 100ma or more will work. 2n4123, 2n2222, mps-a06, etc. I've done 6 or 7 interfaces for ic-730's and they all worked fine after putting the darlington arrangement after the opto. Grin
If someone can tell me how to post a pdf to this forum I could throw up a drawing.
N5CEY Clifford
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