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Audio Line Level

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Tomas White

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Hey guys! So I've set myself out to create this futuristic design having smart speaker, that is so simple to use that you do not even have to turn it on! Removing the On/Off switch was going to be a simple step as I thought at first, however, I am now starting to run in to issues. I have purchased a relay module that senses the input signal 10 - 300 mV max. at a frequency of 30 - 15 000 Hz. All is good and well I have hooked it up to the relay to the source and I've noticed there was not enough voltage going to the relay module to engage the relay itself from the Audio Receiver. I'm using an iPhone and on the range of 16 volume settings my relay did not engage from 1-4. I then connected if to the the module to one of the speakers which receives about 5W from the amplifier and then saw that my relay engages from the 2/16 volume setting on my iPhone. However the trouble there was that the peak voltage from the speaker goes up to 1,4V which is 4 times what the relay is rated for. Do you guys know of any products or have ideas if I should get a weak amplifier and feed the relay from the source thru the amp, or if I should stick to the 5W speaker connection coming from my current speakers amp, but try to convert that AC signal ranging from anything between 0.1V - 1.4V? Again, I have been thinking if I would want to take the signal from a speaker I would need to both up the voltage when its too low and also step it down when it gets too high.

Parts I've used:

And an old Creative t3150 system
 
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you could place a limiter between the high level signal and the relay input, or go back to the line level signal and use an AGC amplifier (automatic gain control) to amplify the signal when it's very quiet, and ramp down to no gain when it's loud. the AGC amplifier would then feed the relay input.
 
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