Yaesu ht PTT circuit?

Discussion in 'General Technical Questions and Answers' started by KD0KKV, Jul 26, 2010.

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  1. KD0KKV

    KD0KKV Ham Member

    I'm trying to make a ptt circuit for the com port on my computer. I'm still not sure which pins on the com port to use. I have the ct-44 adapter and a Yaesu ft-60r. I'm attaching the diagram included in my radio's manual for the ct-44 and a diagram I drew. Can someone tell me if I have this correct?
     
  2. KD0KKV

    KD0KKV Ham Member

    Not sure why they moved this thread from circuits to here instead of digital modes or the audio subforum. I've asked this here before and got nil, and this time I did all the research I could. I guess I should just try it and hope I don't destroy my radio. Can someone at least tell me if that's a possibility?
     
  3. W0HU

    W0HU Ham Member

    Keying circuit

    Hi Scott,

    Your drawing is a little baffling to me, but let me explain how the adapter should work for you:

    To key the transmitter (causing it to transmit), you have to apply "ground" to one side of the 2K resistor that is shown connected to the center pin of the "mic" side of the ct-44 adapter. That should be accomplished by whatever pin in the serial connector is designated "ptt". The "ground" side has to be connected with the "ground" side of the serial connector for this to work.

    Jerry W0HU
     
  4. KF5FEI

    KF5FEI Ham Member

    You don't actually attach your serial port direct to the mic connector. Ideally you should use an opto-isolator, like a 4N28 to make sure you don't damage the radio or PC. The serial port drives an LED in the opto-isolator, which in turn triggers a photo-transistor, which keys the radio. If you Google opto-isolator keying circuit you can find several examples, like this:

    http://www.qsl.net/sv1bsx/keyer/key.htm

    While it is for a CW transmitter, it should work for an HT as well.
     
  5. KC2UGV

    KC2UGV Ham Member

    It's pin 5(GND) and 7(RTS) :)

    What I usually do, in this instance, is I have the GND go to common ground for the circuit, and pin 7 drives a transistor.
     
  6. KD0KKV

    KD0KKV Ham Member

    Thanks for all the information guys. I've decided this is all way over my head and am just going to save up for the pre-made cables since they're only $80. I just don't know enough about resistors and circuitry to pull this off.
     
  7. KC2UGV

    KC2UGV Ham Member

    This is a $20 job in parts... I'd say go for it. Never a better time to learn, right?

    Easy peasy job. 1 transistor, 2 (Maybe 3) mono connectors, 3 resistors, and a diode.
     
  8. KD0KKV

    KD0KKV Ham Member

    Yea, I know its cheaper, I just can't find clear instructions or help on how to construct it :)
     
  9. KC2UGV

    KC2UGV Ham Member

    Well, take the circuit schematic you have, and place a transistor across the "gap". Collector or emitter pins depends on the transistor you use. Connect the base to the RTS pin of the comm port. Voila! You know have PTT control :)

    You may need the diode, may not, depending on the noise. I only needed in on a rig, because if I turned the volume up too high it started to cut in and out.

    Basically, remember: A transistor is a switch, and you are using the "Button" (aka Base) to turn it on. In order to "power the switch", you connect the base to the signal pin (RTS pin in this case).
     
  10. KD0KKV

    KD0KKV Ham Member

    Ok, that makes some sense. What about the ground connection on the com port? Do I just not use that? Also, does a transistor flip with just a jolt, or a constant current? Sorry about all the beginner questions, I'm more of a software guy than hardware.
     
  11. N4CR

    N4CR XML Subscriber

    A transistor requires a bias voltage to turn on, it is not latching. When the com port voltage goes high (RTS), the transistor turns on. When it goes low, the transistor turns off.

    I'd use an opto-isolator instead of a transistor as mentioned before.
     
  12. KC2UGV

    KC2UGV Ham Member

    The opto-isolator would be a better choice. You might be able to scavenge one from an old electronic device which uses a remote control (The Opto-isolator is a 4 pin, sometimes 6 pin, chip right near the IR sensor). Or, buy one brand new.

    The opto-isolator separates the two circuits, so you are almost guaranteed no hum

    The ground pin connects to the circuit's common ground. Be careful though, and read your manual. I know my HTX-420 (Which uses a similar PTT) will get damaged if the rx and tx audio have a common ground.
     
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