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line level input switch

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danrogers

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line level sensor input auto power switch (audio)

hi all. I'm thinking about trying to make a circuit that would automatically switch on my subwoofer when a signal is detected on the line input.

I think line level is around 2v but im not sure on that? Also how would you suggest to avoid it turning off on areas of audio with little or no signals coming into the sub?

thanks
 
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Look at VOX circuits. You would need to determine a delay-off time that would allow for pauses in the bass. But, VOXs also requires a small amount of time between signal onset and turn on.


Ken
 
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The maximum line voltage may be a volt or so, but typically it's less, so you need to detect signals of a few tens of millivolts or so.

You would probably want a delay of at least 30s before turning off the sub after no signal is detected.
 
google seems to chuck up a few circuits designed to work with a microphone level input but not line, how would I need to modify them?
 
Probably just use a couple resistors at the circuit input to attenuate the signal.
 
**broken link removed**

how about this circuit? is there a way to calculate the changes I would need to make to the input side of it for line-in?

thanks
 
What is that circuit for? It has a rather low input impedance of ≈130 ohms so it would appear to be something that was designed to connect to a speaker signal.
 
You might try a VOX kit such as **broken link removed**. It has adjustable sensitivity and the off delay can be adjusted by changing one or two component values.
 
ah ok thanks a line level would probably be to low for those values then?

Im in the UK so that kit might be awkward but thanks anyhow.

Its to switch power on in a home cinema sub that I am modifing slightly. Its not that big, im not sure on the power consumption of the transformer inside but will need it to switch 240v.

thanks for the help by the way
 
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Something like attached might work. R1 can be a pot to set audio sensitivity. R4 sets relay on time for quiet audio spots. You can pick a different comparator, just select one that can detect near the ground rail.
 

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Relay goes in place of R3. See link.
**broken link removed**

Relay_ctrl was just used to give that node a name.It makes reading the waveform file easier.
 
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Thanks Mike, basically the output from the 555 turns on the transistor which sinks current and turns on the relay I think?

and adjusting R5 will leave the circuit active for x amount of time while the auto signal has gone silent?

thanks for the help
 
Thanks Mike, basically the output from the 555 turns on the transistor which sinks current and turns on the relay I think?

and adjusting R5 will leave the circuit active for x amount of time while the auto signal has gone silent?

thanks for the help
R4 not R5 but yup that's about it. Just a disclaimer here. I have not built or tested the circuit, only simulated. There may be unexpected gotchas that I have not accounted for as I put the circuit together in about 30 mins. Depending on what the relay is switching, there may be other considerations to think about.
One thing I just thought about is that the comparator input may be susceptible to outside interference such as RF, EMI etc...
You may want to include a **broken link removed** on the comparator input. Also use shielded audio cable. I am sure if there are any potential pitfalls someone will point it out. :) Have fun.
 
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