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Circuit for switching speaker and LED

declee

Jan 6, 2024
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Greetings! In this project, I'm trying to build a circuit that will engage a subwoofer and an indicator light. My (novice) understanding is diagrammed below. I'm wondering if there are more nuanced details I need to consider. For example, does this setup require a ground? A fuse? I'm also not confident about the DPST switch itself, because it seems the speaker level signals and LED power source are so very different. What sort of DPST switch specs should I consider?
SubSwitch.png
 

Bluejets

Oct 5, 2014
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As shown seems ok depending on just what the LED is (current/voltage)...... BUT......... what happens to the amplifier with an open circuit on the speaker.
Some amps will poke out smoke when this happens.
 

kellys_eye

Jun 25, 2010
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What kind of audio levels are we talking? Anything 'domestic' would easily be handled by standard toggle/rocker switches rated at 125V/3A.

The wiring arrangement you show is fine - no fuse required for the LED as the USB-delivered 5V is 'protected'.
 

declee

Jan 6, 2024
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Thank you for the early feedback and confirmation; this really is my first legitimate DIY electronics project. I've updated the diagram to verify that my wiring logic is sound. Instead of the previous DPST switch, I'll be using a dedicated relay module, which isn't correctly depicted here: it uses the DC 5v, but it's actually the isolated AC audio signal that trips the speaker switch on the module. Aside from the over-simplified relay representation here, is my wiring and component plan okay? My thinking for the 3A fuse is that the power adapter I've chosen for this project is rated for 2A draw, so a 3A draw should signify trouble, right?
SubSwitch2.png
 

kellys_eye

Jun 25, 2010
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Fuses protect cables, not equipment. If the power supply is rated at 2A your cable should be capable of carrying 2A as well but the fuse will do nothing to protect the LED/relay in the event of a fault. A 1A fuse would have been more than adequate.

Other than the pedantics I quote above, the circuit will work as you intend.
 

Harald Kapp

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it's actually the isolated AC audio signal that trips the speaker switch on the module.
Why then do you switch the audio to the speaker, too?
1. Acc. to your description, without Audio the relay will be off and the LED consequently will be off, too.
2. With audio, the relay would turn on and the LEd will be on, too.

In both cases the speaker can be permanently connected to the audio source as in case 1 there is no audio to drive the speaker and in case 2 the audio is expected to drive the speaker.

What module are you planning to use? Post the type or even better a link to the product.
Any such circuit will need a certain minimum audio level to be activated which in turn means that at very low audio levels the relay may click on and off more or less randomly. No problem for the LED but bad for your listening experience.

What is the purpose of your circuit?
A very simple circuit for indicating the presence of an audio signal is shown on this website (2nd circuit from top). Comes with adjustable sensitivity.

How sensitive does the circuit have to be? Depending on the amplitude of the audio signal (in essence the volume) a simple passive circuit may suffice, like so:
1704822659783.png
The value of may have to be adjusted the level of the audio signal. Since it is passive, this circuit will only work at medium to high signal levels.
 

Harald Kapp

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I'm trying to build a circuit that will engage a subwoofer and an indicator light.
Reading back to the beginning of this thread I found the above remark. Is that a passive subwoofer or an active one?

In case of a passive subwoofer my remarks in post #7 with respect to powering the subwoofer are still valid.

In case of an active subwoofer your circuit diagram is misleading. In such a scenario you wouldn't switch the audio signal by the relay, rather the relay would switch the power to the subwoofer. Many active subwoofers have such a circuit built into them to save power when no signal is present.
In this case the relay module will not only have to detect the audio signal, it will also need to have a timer to bridge gaps in the audio signal for a few minutes. That prevents the subwoofer from turning off an on repeatedly during breaks in the music (between tracks, when changing disks, ...)- Here's an example of a module for this exact purpose. Or a circuit diagram for a DIY module if you are inclined to build one.
 

declee

Jan 6, 2024
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Reading back to the beginning of this thread I found the above remark. Is that a passive subwoofer or an active one?

In case of a passive subwoofer my remarks in post #7 with respect to powering the subwoofer are still valid.

In case of an active subwoofer your circuit diagram is misleading. In such a scenario you wouldn't switch the audio signal by the relay, rather the relay would switch the power to the subwoofer. Many active subwoofers have such a circuit built into them to save power when no signal is present.
In this case the relay module will not only have to detect the audio signal, it will also need to have a timer to bridge gaps in the audio signal for a few minutes. That prevents the subwoofer from turning off an on repeatedly during breaks in the music (between tracks, when changing disks, ...)- Here's an example of a module for this exact purpose. Or a circuit diagram for a DIY module if you are inclined to build one.
Right: the module is similar to the one you referenced. As I wrote, my diagram simplifies the entire module piece because I didn't know how to depict it with standard symbols. Thus, the entire module is represented at the point I show a relay. Thanks!
 

declee

Jan 6, 2024
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Fuses protect cables, not equipment. If the power supply is rated at 2A your cable should be capable of carrying 2A as well but the fuse will do nothing to protect the LED/relay in the event of a fault. A 1A fuse would have been more than adequate.

Other than the pedantics I quote above, the circuit will work as you intend.
Smaller fuse, got it! Thank you :)
 
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