Turn on a switch from audio jack.

[spec]

Thanks again spec,
What is the benefits of the opamp in this application and how fast would it turn on as compared to the lesser circuit? A very fast turn on would be important to me.
Thanks.

Hi Baxter

This version 3 audio detector and switching circuit is much better toleranced and predictable.

The turn on delay would be about 50mS as opposed to around 500mS for version 2 (depending on the individual transistor characteristics).

As the MOSFET will turn on and off fast (due to the Schmidt trigger formed by the second opamp), the dissipation in the MOSFET in version 3 will be greatly reduced.

The loading on the audio input is less with version 3 of the circuit.

Version 3 will have more flexibility so that the sensitivity and the timing can be more easily adjusted.

Version 3 will be less dependent on component characteristics than version 2. After a detailed analysis I found that the performance of version 2 depended rather heavily on the characteristics of the input transistor.

Version 3 will be less susceptible to noise and interference.

In conclusion, I would recommend that you go for version 3 of the circuit.

spec

 

[baxterdmutt]

Hi Baxter

This version 3 audio detector and switching circuit is much better toleranced and predictable.

The turn on delay would be about 50mS as opposed to around 500mS for version 2 (depending on the individual transistor characteristics).

As the MOSFET will turn on and off fast (due to the Schmidt trigger formed by the second opamp), the dissipation in the MOSFET in version 3 will be greatly reduced.

The loading on the audio input is less with version 3 of the circuit.

Version 3 will have more flexibility so that the sensitivity and the timing can be more easily adjusted.

Version 3 will be less dependent on component characteristics than version 2. After a detailed analysis I found that the performance of version 2 depended rather heavily on the characteristics of the input transistor.

Version 3 will be less susceptible to noise and interference.

In conclusion, I would recommend that you go for version 3 of the circuit.

spec

Spec,
Great, that sounds perfect. Now I just have to find the time to put it together.
I'm thankful that you've taken this much time to do this for me. You've saved me a ton of time.

 

[spec]

Spec,
Great, that sounds perfect. Now I just have to find the time to put it together.
I'm thankful that you've taken this much time to do this for me. You've saved me a ton of time.

No problems Baxter,

Once again I hope that circuit version 3 works OK. It is a bit more complex than the version 2 circuit but the cost of the parts is not great and I think you would be better off investing your time in Version 3.

spec

 

[cowboybob]

Hello, Baxter. I've being fllowing this thread and thought I'd throw in my 2 cents worth (with all due respect to spec ).

Circuit below is a pretty simple 555 timer set up. Biasing of the 2N2222 may need to be adjusted a bit for your situation. "Audio In" levels will also affect response. C2 and the timer pot can also be changed to suit your "Amp on duration" needs.
Note 5% setting of pot for the first graphing...

and the 100% setting for this one.

My "Audio In" is from a bass guitar .WAV file. With no audio in, the bias 0.621 Vdc. Some of it is lost in C1.

73s
Paul

 

[spec]

Hi Paul,

Pretty neat idea using a 555 for this application.

(perhaps put a 4.7K resistor in series with the input transistor and make R1= 100K)

Chuck

 

[baxterdmutt]

Hello, Baxter. I've being fllowing this thread and thought I'd throw in my 2 cents worth (with all due respect to spec ).

Circuit below is a pretty simple 555 timer set up. Biasing of the 2N2222 may need to be adjusted a bit for your situation. "Audio In" levels will also affect response. C2 and the timer pot can also be changed to suit your "Amp on duration" needs.
Note 5% setting of pot for the first graphing...
View attachment 101429
and the 100% setting for this one.
View attachment 101430
My "Audio In" is from a bass guitar .WAV file. With no audio in, the bias 0.621 Vdc. Some of it is lost in C1.

73s
Paul

Thanks Paul.
This is kinda what I was initially thinking of doing but without a timer circuit and without the relay. I was going to just do the on/off switching with a transistor. I feel bad because I now realize that the circuits that have been designed for me can handle way more than the 66ma that the amp would draw on these circuits. I'm not having to switch on the power to the amp, just the built in relay (probably a transistor or MOSFET inside it). I thought I mentioned that but looking at what I wrote I see I didn't. I hope I haven't wasted anyone's time. All the circuits will work for me so from my point of view I'm golden and you guys have been great. I like the 555 timer idea. I never thought of adding that. That idea could come in handy depending on how irritating it could be having the amp click off and on with closely followed transmission.

 

[baxterdmutt]

I do have a question that I still don't understand. I thought audio was more an alternating current than it was dc. But to me it doesn't look like any of these circuits rectify the voltage to dc. Am I missing something?

 

[spec]

Thanks Paul.
This is kinda what I was initially thinking of doing but without a timer circuit and without the relay. I was going to just do the on/off switching with a transistor. I feel bad because I now realize that the circuits that have been designed for me can handle way more than the 66ma that the amp would draw on these circuits. I'm not having to switch on the power to the amp, just the built in relay (probably a transistor or MOSFET inside it). I thought I mentioned that but looking at what I wrote I see I didn't. I hope I haven't wasted anyone's time. All the circuits will work for me so from my point of view I'm golden and you guys have been great. I like the 555 timer idea. I never thought of adding that. That idea could come in handy depending on how irritating it could be having the amp click off and on with closely followed transmission.

Hi Baxter,

You have no reason at all to 'feel bad'. I like the challenge of evolving circuits, rather like some people do cross word puzzles and, to me, the more circuits that are posted the better. I even appreciate it if someone finds a valid error in my circuits. The other thing is that you nearly always learn something new when you respond to a question on ETO. It is totally up to you to chose which circuit you would like to use.

spec

 

[spec]

I do have a question that I still don't understand. I thought audio was more an alternating current than it was dc. But to me it doesn't look like any of these circuits rectify the voltage to dc. Am I missing something?

Hy Baxter,

It is quite true that audio is an AC signal. In fact audio comprises a mixture of AC signals (sine waves) in the frequency range 20Hz to 20KHz. Generally, the amplitude of the AC signals in an average audio signal reduces as the frequency increases.

You are quite right: circuits version 1 and 2 do not have rectifiers as such, but circuit version 3 does.
(1) In version 1 and 2 circuit, the input transistor only conducts on positive excursions of the the input sine waves. The transistor does not respond to the negative part of the sine wave. When the transistor conducts it discharges the capacitor, which causes the PMOSFET to turn on (gate negative).
(2) In version 3 circuit, the first opamp charges the capacitor to the positive peak voltage of the input sine wave (peak detector) via the transistor. In this case the transistor acts like a diode (with current gain to charge the capacitor fast). The transistor turns off when the transistor's base is less than 600mV with respect to the transistor's emitter. The positive voltage on the capacitor causes the Schmidt trigger, formed by the second opamp, to flip and turn the PMOSFET on (gate negative).

spec

 

[cowboybob]

(perhaps put a 4.7K resistor in series with the input transistor and make R1= 100K)

You can add an input resistor if you like - sort of depends on the input sig's level, but R1 is part of the voltage divider (R3 & R1) providing the "helper" bias of the 2N2222.

... the input transistor only conducts on positive excursions of the the input sine waves. ...

As spec points out,we're only interested in a positive going input signal's variations as a trigger to fire the NPN input transistor into conduction. In my circuit's case, this takes the positively biased trigger of the 555 to ground, thereby starting its timed (and variable), monostable output.

I'm not having to switch on the power to the amp, just the built in relay (probably a transistor or MOSFET inside it).

Swap out the relay with another 2N2222 (or equivalent NPN) switch:
Currently:

Positive trigger for amp:

Negative trigger for amp:

Adjust R5 to alter "Amp trigger" level appropriate for the Amp relay controller.

 

[baxterdmutt]

Hy Baxter,

It is quite true that audio is an AC signal. In fact audio comprises a mixture of AC signals (sine waves) in the frequency range 20Hz to 20KHz. Generally, the amplitude of the AC signals in an average audio signal reduces as the frequency increases.

You are quite right: circuits version 1 and 2 do not have rectifiers as such, but circuit version 3 does.
(1) In version 1 and 2 circuit, the input transistor only conducts on positive excursions of the the input sine waves. The transistor does not respond to the negative part of the sine wave. When the transistor conducts it discharges the capacitor, which causes the PMOSFET to turn on (gate negative).
(2) In version 3 circuit, the first opamp charges the capacitor to the positive peak voltage of the input sine wave (peak detector) via the transistor. In this case the transistor acts like a diode (with current gain to charge the capacitor fast). The transistor turns off when the transistor's base is less than 600mV with respect to the transistor's emitter. The positive voltage on the capacitor causes the Schmidt trigger, formed by the second opamp, to flip and turn the PMOSFET on (gate negative).

spec

Spec, thanks that makes sense. This has been very educational. I'm hoping to get to this on the weekend.

 

[baxterdmutt]

You can add an input resistor if you like - sort of depends on the input sig's level, but R1 is part of the voltage divider (R3 & R1) providing the "helper" bias of the 2N2222.

As spec points out,we're only interested in a positive going input signal's variations as a trigger to fire the NPN input transistor into conduction. In my circuit's case, this takes the positively biased trigger of the 555 to ground, thereby starting its timed (and variable), monostable output.

Swap out the relay with another 2N2222 (or equivalent NPN) switch:
Currently:
View attachment 101434
Positive trigger for amp:
View attachment 101438
Negative trigger for amp:
View attachment 101437
Adjust R5 to alter "Amp trigger" level appropriate for the Amp relay controller.

Cowboy,
Very good. I could have figured this part out but I nevertheless appreciate that you did it for me. I have to divide which of these to put together now. Probably my hardest decision now!

 

[MikeMl]

I throw my hat into the ring, too.

This VOX circuit uses readily available components (almost any NPNs will work), operates from 12Vdc (likely the same supply that runs the radio and audioamp), has fast attack time, adjustable hold time, will work with audio from a headphone jack on Ham rig, and is not effected (much) by the volume control setting on the radio.

Q1 is an AC-coupled limiting amplifier and detector (makes it volume insensitive). Q2 is a DC-coupled emitter-follower relay driver. C2 sets the hold time. Make it bigger if you need longer hold time. If you modify R3, the relay could have a 9V, 8V, 6V or 5V DC coil.

The simulation is repeated with bursts of 500Hz audio at amplitudes of +-500mV to +-4V to show that the relay pick-up and release is quite independent of audio amplitude.

 

[baxterdmutt]

I throw my hat into the ring, too.

This VOX circuit uses readily available components (almost any NPNs will work), operates from 12Vdc (likely the same supply that runs the radio and audioamp), has fast attack time, adjustable hold time, will work with audio from a headphone jack on Ham rig, and is not effected (much) by the volume control setting on the radio.

Q1 is an AC-coupled limiting amplifier and detector (makes it volume insensitive). Q2 is a DC-coupled emitter-follower relay driver. C2 sets the hold time. Make it bigger if you need longer hold time. If you modify R3, the relay could have a 9V, 8V, 6V or 5V DC coil.

The simulation is repeated with bursts of 500Hz audio at amplitudes of +-500mV to +-4V to show that the relay pick-up and release is quite independent of audio amplitude.

View attachment 101447

MIke,
Thanks for this. It was very close to the idea I had. So it's the one I've tried first. It's also the quickest one to throw together. It does work but the problem I'm having is that on low volume it kicks off. I'm not sure if adjusting R2 and/or R1 would help with that. As shown it cuts off between speaking the words "Testing,one,two,three" so I've increased c2 to 10uf and in the brief moment I had before I got called away, at least that part seemed better but that of course doesn't help on low volume.
Thanks.

 

[baxterdmutt]

MIke,
I'm not sure if adjusting R2 and/or R1 would help with that. As shown it cuts off between speaking the words "Testing,one,two,three" so I've increased c2 to 10uf and in the brief moment I had before I got called away, at least that part seemed better but that of course doesn't help on low volume.

On looking closer I realized that if I completely remove C1 from the circuit the low volume issue is fixed as long it's a steady tone (like forcing the squelch open or humming into another radio on the same frequency.). If the volume is low and you're speaking words with sufficient space between them, it will cut out after C2 is depleted and it won't come back on without retransmitting a signal from the other radio(even yelling into the radio won't bring it back). I think what happens on low volume is the first spike that comes through when the squelch opens is enough to charge up C2 but as you speak there is insufficient energy to keep C2 charged. That's my theory anyway

 

[MikeMl]

I have done this before. Plugging into the headphone jack on most radios cuts out the internal speaker, removing the 8 Ohm load. The voltage between tip and sleeve is easily more than 500mV at any reasonable volume control setting. I do not understand why the volume needs to be set low. What happens if you simply turn up the volume?

 

[MikeMl]

I have done this before. Plugging into the headphone jack on most radios cuts out the internal speaker, removing the 8 Ohm load. The voltage between tip and sleeve is easily more than 500mV at any reasonable volume control setting. I do not understand why the volume needs to be set low. What happens if you simply turn up the volume?

 

[baxterdmutt]

I have done this before. Plugging into the headphone jack on most radios cuts out the internal speaker, removing the 8 Ohm load. The voltage between tip and sleeve is easily more than 500mV at any reasonable volume control setting. I do not understand why the volume needs to be set low. What happens if you simply turn up the volume?

Hi Mike,
It works if I turn up the volume but it has to be too loud or it's choppy. Maybe it's because this is squelched audio from a portable transceiver. I don't know why, but maybe they've done something different with the audio gain on this device.

 

[baxterdmutt]

Hy again Baxter,

Here is a better defined circuit which switches the 12V on and off sharply after a short delay to turn on and about a second to turn off.

spec

View attachment 101428​

Spec,
I finally got around to putting this one together on the breadboard and it stays on (high) all the time even without the audio connected. I have checked all my connections so I thought I'd see if you had any ideas.

 

[baxterdmutt]

Spec,
I finally got around to putting this one together on the breadboard and it stays on (high) all the time even without the audio connected. I have checked all my connections so I thought I'd see if you had any ideas.

Spec,
Disregard my last post. I feel dumb now. Always read the component before using! I had one remaining lm358n that was left in the little plastic bag that it came in. The bag had the component id printed on it but when I look now it's an lm741. There's a good reason why this isn't working!