Goal: feed audio from a PC to a circuit that will trigger a relay

Thread Starter

DavidDavidScollay

Joined Dec 5, 2021
25
There is a PC-based ham radio communications protocol which sends a series of tones for about 15 seconds seconds. Then for the next 15 seconds it "listens" to tones from the other station. After two more 15 second bursts the PC then records the exchange between the two stations.

What I want is for the audio from the PC (those tones) to do two things: feed audio to an HTX-10 ham radio (this is straight-forward, already designed a pad) but the second part is where I'm having trouble. I want the audio to also trigger a circuit (a VOX, perhaps?) which will provide +12 to the resistor in the relay circuit. (The relay is needed because in receive, the radio requires mic pin 2 to be grounded, with pin 3 NC. To transmit, pin 2 become NC and pin 3 goes to ground.)

Hope I've explained this well enough. I tried to do this with a 555 in monostable mode, but was unable to make it work. All ideas are welcome.
HTX-10 FT8 Interface.jpg
 

Thread Starter

DavidDavidScollay

Joined Dec 5, 2021
25
Here's a circuit that will drive a 60ma 12 volt relay with less then .5 volt p-p audio.
View attachment 254281
wow, thank you for this. a couple of questions:
1. The same audio from the PC that triggers the relay through this circuit also feeds the radio, do I just tap the audio before the transformer or right after?
2. You specify .5v p-p, so I will have to lower the audio level from the PC, correct?

Oh, and the relay is a TQ2-12v DPDT. https://4donline.ihs.com/images/Vip...8-1.pdf?hkey=52A5661711E402568146F3353EA87419

I am currently using a 2N3904 to drive the relay (see my original post) so I guess this circuit should be able to drive the relay as well?
 

sghioto

Joined Dec 31, 2017
3,069
For complete isolation after the transformer at C1.
You don't have to reduce the audio level if it works OK with the radio.
You can tie the collectors of Q2 and Q4 together to drive the relay manually or through the tones
 
Last edited:

LowQCab

Joined Nov 6, 2012
1,931
It would probably be a good idea to design a Filter that will only pass the Frequencies of the Tones.
Although this probably isn't necessary if no other communication is mixed-in.
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Thread Starter

DavidDavidScollay

Joined Dec 5, 2021
25
As you can see in the photo I have bread boarded up the circuit. I’ve checked the circuit three times but still the radio goes into transmit as soon as the circuit is plugged in to the mic Jack. This is even before plugging in laptop audio to the isolation transformer.

Have I placed R5 and D3 correctly- you wrote TX 12v - is that just the + supply or a pin on the relay? What do the resistor and backwards diode do?

thanks, David
 

Attachments

sghioto

Joined Dec 31, 2017
3,069
D3 and R5 are just an external way of operating the relay. D3 would normally connect to a open PTT switch to 12 volts. If you don't need an external PTT switch you can remove D3 and R5. Sorry for the confusion.
1638821971345.png
 

Thread Starter

DavidDavidScollay

Joined Dec 5, 2021
25
OK I removed both those components since I don’t need PTT.

same issue even with the laptop unplugged from the circuit as soon as I connect the collector of Q2 to pin 10 of the relay the relay engages.
 
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