Repeaters: 146.700- Mhz | 146.970- Mhz | 443.700+ Mhz | 445.075- Mhz | PL: 100 hz

Time-out timer for computer controlled radios.

Last week the echolink computer had a hard crash and kept the PTT closed. Luckily the local repeater has a time out timer so the TX lock up did not killed the repeaters finals, but nobody could access the repeater for a couple of hours due to the input being locked.

The suggestion was to enable TOT on the radio, but the radio is an older  Azden PCS 7000 that does not have this feature.

The way how the PTT is activated from the computer is through the serial port. The signal RTS is set to high and together with the ground it closes the PTT, either by using an opto-coupler or a transistor. The solution I thought about was using the PIC12F683 and is described bellow.

The PIC12F683 is a small 8 pins micro controller. You can define what the pins do and load it in to the part. I used the RTS signal from the computer to power up the PIC. The PIC was loaded with a C++ code that set one output to high, waits 3 minutes and 20 seconds and then set it to low.

The code was written using the demo version of the MikroC from Mikro Elektronika. The demo version is good enough for this little program:


void main() {
ANSEL = 0;          // Turn off analog input
CMCON0 = 0x07;      // Turn off Comparators
TRISIO = 0x00;      // Set all pins as output
GPIO = 0xAA;        // Set Pattern 10101010

Delay_ms( 200000);  // Delay in ms 200000 = 3 mins, 20 seconds
GPIO = ~GPIO;       // Invert pins
}

 

The components I used were:

  1. Radioshack 276-1537 – 9 Position-Male D-Sub connector
  2. Radioshack 276-1538 – 9 Position-Female D-Sub connector
  3. Radioshack 276-148 – General Purpose Dual PC Board (used only 1)
  4. Microchip pic 12F683 – Microchip has free samples, you can buy them from anywhere, mouser, jameco, digikey, etc.
Parts

Besides that you will also need a pic programmer available for purchase on the internet or you can build your own.  Soldering iron, solder and a small amount of wire.

The circuit is as follow:

Schematics

Other pictures:

Back
Front

At the end the project worked as expected on the first test run, cannot complain about that. If you wish to duplicate this and have any questions or comments, please leave a message bellow, I will try to answer your questions.

73′ s de KC2UEZ

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3 thoughts on “Time-out timer for computer controlled radios.

  1. EDGAR
    NICE JOB BUT I DON’T HAVE A CLUE WHAT YOUR TALKING ABOUT…BUT NICE JOB ANYWAY…I’M NOT VERY ELECTRICAL AS YOU KNOW….I HOPE I CAN DO THE MATH THAT IS REQUIRED AT THE BOTTOM TO PROVE I’M NOT A ROBOT…HI HI

  2. Great Job Edgar!

    Glad we have you as part of our group as most of the rest of us would be lost without your help.

    Thanks

    Steve

  3. Nice job as always Edgar, you make it seem so easy.. Glad to have you on our team, like Steve said, we’d be lost without you!!

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