Most desktop systems use a 12 volt standard, and laptops 5 volts. Troubleshooting showed me that my laptop was only putting out 5 volts.
I put in a 1.2k resistor, and nothing happened. On my initial design, I assumed we were dealing with 12 volts. Breakdown voltage is only 6 volts, so we better put a dropping resistor in there! I put the reverse bias diode, so if we have reverse voltage, it has somewhere to go, and doesn't build up to the breakdown voltage. This LED only requires 1.18 volts (1.5 max) with a current draw of 100mA. Since the only connection is light, you maintain your isolation. When you light up the LED, the transistor conducts. Inside the opto isolator, there is an LED and a phototransistor. Unfortunately, this does NOT provide total electrical isolation. one way is with a transistor as a switch. This circuit could have been done several ways. On my ham rig, the ptt circuit floats high, and when you pull it down, you transmit.
#Interface rtty software
What this means, is when the software wants to transmit, that pin goes high (positive voltage). Most software will toggle either the RTS or the DTR line. Next, you need to control transmit / receive. This completes the audio portion of the circuit. Every piece of software I looked at uses the left channel (tip), so connect there.
#Interface rtty Patch
The cable I used was an old shielded patch cable, which I cut the RCA ends off. This is only so I can tell which one is which. In the pictures you will notice that I have one plastic plug, and one metal one. Since I didn't want any possibility of ground loops, I did not connect the grounds together.
#Interface rtty windows
I was able to use the sound control panel within Windows for all my audio adjustment. Computer sound cards are also at line level, so this part is super simple. I was happy to discover during testing that both the modulator input and the output on the 13 pin connector are at line level. You do not want to use step-up or step-down, as they will change the levels. The audio is coupled through 1:1 transformers. I found one at HRO - it is for a Kenwood, but they are universal. The only part I had trouble finding was the 13 pin DIN connector. I do NOT recommend Radio Shack for parts, as they are very overpriced, if they even have the part! If you do not have an electronics store in your neck of the woods, I would suggest looking online. For the parts I did not have, I found them at All Electronics, which is a electronics surplus store about 10 miles from work. Many of the parts I used were from my junk box. Computer hash in your HF rig will make you miserable, and RF in the computer.isn't Windows unstable enough? You don't want to create ground loops connecting it all directly. The main purpose of this device is to provide total isolation between the computer and the rig. As a bonus, If I can build it myself - need I say more? Since I know that I can not be cured, I had to put it to use.
#Interface rtty manual
After purchasing my Icom IC-718, I discovered the page in the manual where that mysterious 13 pin accessory connector on the rear was documented.
I am the type of person who likes to push every button, twist every knob, and try every option on any piece of electronics I get my hands on. I used one plastic one and one metal one to tell them apart. (1) RS-232 Cable (mine was an old Null Modem Cable). Kenwood rigs have a similar port, however the pin outs are different so beware! This should work on any Icom rig that has a 13 pin accessory port, however I have only tested it on my 718. This was designed and tested on an Icom 718 HF rig and a Dell laptop. If you don't, hey, no hard feelings, but if you do and mess something up, don't blame me. Do this at your own risk! It's your choice to do this. WARNING! This page describes a modification that you plug in to your radio and computer. KG6MVB's Rig to Computer interface KG6MVB's Rig to Computer interface for Icom 718
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