First you can try increasing the value of C1 and R4. If that doesn't work well enough leave C1 at 1uf and add transistor Q4 to make a darlington and increase the value of R4 as needed.
SG

 

Sorry, would have tried it tonight, but didn't realize there was a second page until now and don't have enough time to change it tonight.

Again thanks for the help.

 

Thanks for the replys. Now I just got to take a radio apart now to figure out the circuit.

If the radio has a "BUSY" indicator that lights up when the squelch breaks then that is the point to connect a high impedance sense circuit, such as a CD4049 or CD4050. But first you need to measure and see what the voltage is and what the change is. That may be a challenge.

 

First you can try increasing the value of C1 and R4. If that doesn't work well enough leave C1 at 1uf and add transistor Q4 to make a darlington and increase the value of R4 as needed.
SG
View attachment 146034

Thanks sghioto and sorry for the delay.

That circuit worked perfect for a 2 second delay, but there was not enough voltage to keep it latched open, so I added a lm358 to boost the voltage and then it worked perfect.

 

If the radio has a "BUSY" indicator that lights up when the squelch breaks then that is the point to connect a high impedance sense circuit, such as a CD4049 or CD4050. But first you need to measure and see what the voltage is and what the change is. That may be a challenge.

The voltage coming out of the headphone jack is approximately 0.25 v then drops to 0.02 volts on volume level 2 of 7 measured with a Fluke 117 in AC volts min/max mode.

 

The voltage coming out of the headphone jack is approximately 0.25 v then drops to 0.02 volts on volume level 2 of 7 measured with a Fluke 117 in AC volts min/max mode.

There is a circuit that uses a 555 timer IC to drive the relay and uses op-amps for the control signal to trigger the timer. The benefit of using a trigger system instead of an amplifier is that when the signal is above the trigger point the relay stays triggered for a while. You could also just use a simple 358 op-amp with the first section as a gain amplifier and the second section as the comparator to trigger the timer. This is about as small a package as you can get without needing to go to surface mount stuff that is hard to work with. Also, it is cheap and easy to understand.

 

MisterBill2,

The circuit currently works perfect. The audio goes through the op amp to increase the signal from the 2 way because the signal before was enough to trigger the transistors but not enough to hold them open and the capacitor holds it open for roughly 2 seconds which is perfect. So, a 555 timer is not needed.

I figured out the push to talk feature for the Mic by adding a switch to turn the Mic on and off.

Now, the problem I am having is the relay that I have won't pass audio signal through it. Using the multimeter when I see it switch back and forth and have a resistance of roughly 0.4 ohms.
The relay works correctly as well after I rewired it the correct way.

So do I have to go with a multiplexer, like ADG5236?

Thanks for all the replys so far.

 

Now, the problem I am having is the relay that I have won't pass audio signal through it. Using the multimeter when I see it switch back and forth and have a resistance of roughly 0.4 ohms.

Why wouldn't it pass audio? What relay are you using and how is it connected in the circuit?
SG

 

Never mind got sound once connected correctly miss read the diagram on the bottom and connected the leads wrong.

 

It happens to all of us.
SG

 

Here I drew up a Schematic of the finished circuit. Will you take a look at it and make sure it is within specs so I don't blow anything up once in use.

Note: C1 is a measured value of the cap and 2032 is the label on it.

 

Here I drew up a Schematic of the finished circuit. Will you take a look at it and make sure it is within specs so I don't blow anything up once in use.

The vox circuit looks OK from what I see, not exactly sure of the "how and why" of the audio through the relay contacts but if you say it works then fine.
My only suggestion would be replacing Q1 and Q2 with the other half of the LM358.
SG

 

Thanks sghioto,

I was able to remove the Q1 and Q2 and avoided using the other half of the LM358 by increasing the gain from 11 dB to ~23 dB by swapping out R2 with a 68k resistor.

I also removed D1, C1, R3, R4, and R5.

I added R9 and R10 to allow some music into the headphones when you are receiving a signal from the 2 way. I also added C3, C4, R7, and R8 for a High Pass Filter because I get a pop when the relay makes and breaks contact.

The reason for audio through relay contacts is so the music will get muted (or turned down way low) so the voices on the 2 way will stand out and will not be drowned out by the music. That is why the audio is going through a relay.



That is my updated circuit.

Thanks again,
FF

 

Nice job! Circuit looks clean and lean.
EDIT: I would just add that the unused input pins 5 and 6 on the LM358 should go to there respective logic levels i.e. pin5 to Vcc and pin6 to Gnd.
SG

 

Nice job! Circuit looks clean and lean.

Thanks sghioto.

Removed the High Pass Filter because one it created some weird feedback and two it did not remove a pop or click noise when the two way kicked in so I believe it is coming directly from the 2-way so I don't need it.

After looking at the datasheet one more time I seen it said to add a 0.1 uF capacitor on the power in of the op-amp. Also I tied neg. input to output and pos. input in between two 100k resistors from 12v to gnd.



Now the power source will be a running vehicle so, should I add some kind of filter to the circuit to limit electrical noise from the charging system?

Thanks,
FF

 

Now the power source will be a running vehicle so, should I add some kind of filter to the circuit to limit electrical noise from the charging system?
Thanks,FF

That's a good idea. Usual components are a choke or coil and a large value cap.
SG