Motion switched/controlled speaker volume

BradsXmasLights

BradsXmasLights

WiFi Interactive
Joined
Dec 23, 2010
Messages
605
Location
Brisbane, Australia
I have installed a small set of computer speakers inside my letterbox. I've kept the volume very soft so it doesn't annoy the neighbours - but if I see people standing out the front I'll turn up the volume (from inside the house).

This has me thinking - any one know of a circuit/kit can could be wired to a PIR to adjust volume accordingly? Or even just switching the speakers on/off... PIR >> Relay on + countdown timer started >> Relay off > > speaker's 12VDC power ???

Any one got a similar idea?
 
Some PIRs have an adjustable time that the output stays on for after the source of the trigger ceases. Other than that, Jaycar probably sells a simple relay timer board kit which could extend the trigger pulse from a standard PIR.

For a powered speaker, you'd have a line level audio signal. It would be a simple matter to hook up a relay and potentiometer (volume control) in line with that signal. When triggered (people present), the extra volume control would be bypassed. Once the relay drops back off (people gone), the volume control would be in circuit.

You'd set the maximum level you want (relay triggered mode) via the usual volume controls on the computer and/or speaker. The extra (relay controlled) would set the amount of reduction when nobody is around.

Make sense? I can draw a nice diagram if required.
 
I've assumed mono, but for stereo you could use a double pole relay and dual gang pot.

The 100K resistor is optional but may help eliminate any transients (click / pop) as the relay switches over.
 
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