Using a PTT desk mic on a PC

So in this post, I'm going to talk about a cool project that I finished a few weeks ago.  I like to use EchoLink (http://www.echolink.org/) to chat with people all over the world.  One of the uses for EchoLink, and the only thing that I use it for, is to connect to a repeater that you are too far away to hit using RF alone.  This software connects you to that repeater, and broadcasts what you say into your PC mic as if you were using a radio.  That being said, I like to feel like I am talking into a real rig, instead of talking on Skype or some other VoIP application when I am using EchoLink, especially since it is only accessible by other licensed Hams.  To that end, I had an old mic laying around, so I decided to connect it to the computer.  There were several obstacles that needed to be surmounted, the first being that the mic used an 8-pin connector for Kenwood HF radios, and the second being that you needed the press the PTT (Push-To-Talk) button in order for your audio to be sent out of the mic's audio pins.  The final issue was that the EchoLink software needs to be "keyed" as well by pushing down the space bar on your PC.  Here is how I solved these issues:

To convert from 8-pin to something that the PC could accept, I wired up the audio pins from an 8-pin male connector (the mic has a female, although it seems as though the names should be reversed) to an 1/8" female audio jack.  I mounted both in a small project box to make the assemblage a little easier to use.  This took care of getting the audio into the PC, but I still had to hit the space bar to "key" EchoLink, and at the same time hit the PTT button on the mic to connect the mic element to the audio pins inside the mic.  This was annoying to say the least.  Enter the Teensy USB Development Board:

This board connects to the PC and is recognized as one of several devices, a keyboard, a flash device, a MIDI device, etc.  The main one that I am concerned with was the ability to emulate a USB keyboard.  I soldered a connection from the PTT pins in the mic jack to one of the digital pins on the Teensy board, and another one to the ground pin.  This allows me to detect when the PTT button is depressed on the mic.  I then took this detection, and triggered a key press event to key EchoLink!  Now I can use EchoLink just like a normal radio, via the desk mic, without keyboard input.  Just for fun, I added a red LED to know when the mic PTT key is depressed (to hopefully avoid "hot-mic" issues).

My Parts List:

• 1 x Teensy USB Board ( http://www.pjrc.com/teensy/)
• 1 x Project Box
• 1 x 8-pin male mic connector
• 1 x 1/8" (3.5mm) audio connector
• 1 x Red LED
• 1 x 220-Ohm resistor

Time to Completion:

• About four hours including figuring out the code for the "sketch" on the Teensy board.

Here is the simple schematic:

Here are a few pics:

Here is the code that I used on the Teensy board (which uses the Arduino IDE environment):


#include <Bounce.h>


Bounce button0 = Bounce(0, 10);


void setup() {
  pinMode(0, INPUT_PULLUP);
   pinMode(12, OUTPUT);
}


void loop() {
  // Update all the buttons.  There should not be any long
  // delays in loop(), so this runs repetitively at a rate
  // faster than the buttons could be pressed and released.
  button0.update();


if (button0.fallingEdge()) {
   // press and release CTRL
   Keyboard.set_key1(KEYPAD_PLUS);
   Keyboard.send_now();
   Keyboard.set_key1(0);
   Keyboard.send_now();
   analogWrite(12, 200);
  }


 if (button0.risingEdge()) {
   // press and release CTRL
   Keyboard.set_key1(KEYPAD_PLUS);
   Keyboard.send_now();
   Keyboard.set_key1(0);
   Keyboard.send_now();
   analogWrite(12, 0);
  }
}

Well, that's all for this post, I hope that you have enjoyed it, I certainly enjoyed making it!

73,

Richard, KK4JDO