Filter to pass this sound?

I use this battery operated irrigation unit from about May to November to water garden plant pots and hanging baskets:

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I'm thinking of improvising a circuit to let me use it as a timer for other indoor purposes during the rest of the year. Such as burglar deterrent lamp switching, etc, capitalising on its neat setting controls.

I'm reluctant to hack into its well-hidden circuitry, and also risk its weatherproofing. So I'd need to front it with a microphone and filter to detect the sound it makes when it switches on or off:

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What would be a good starting point for a band pass filter for that

4-second noise please?

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As a side question, anyone know whether there's a web-based tool onto which I could drop that WAV file and get suggested passive or active filter circuits?

Terry, East Grinstead, UK

Reply to
Terry Pinnell
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I think if the microphone is in contact with the box, all you'd need is to amplify, then diode and capacitor to get DC level, then detect above a threshold for >3 seconds continuous.

Cheers

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Clive
Reply to
Clive Arthur

There are web-based tools to assist with filter design from a set of requirements/parameters but I don't know any you can upload a .WAV file to; they're just kind of dumb mathematical tools they don't "know" what it is you're trying to do.

Once you have a plausible test filter though it can be simulated in LTSpice and you can use a .WAV file as input signal data and generate a .WAV file with the filtered output run through the "virtual" circuit.

Tangentially for anyone who's interested there's a web-based service that uses AI/neural network to take fully mixed audio tracks with music and vocals and separate it out into instrumental and vocal components, it's not perfect but does a better job of it than any other commercial software boxes or commercial hardware that purports to accomplish this that I've tried. (no financial affiliation)

Reply to
bitrex

Thanks Clive, my design idea was a tad OTT!

Terry, East Grinstead, UK

Reply to
Terry Pinnell

Thanks bitrex. I do have LT Spice but have mainly used CircuitMaker 2000 for simulation. Long time since I did so in earnest, but I'll try it with whatever circuit emerges. Probably the much simpler one Clive suggested, as I don't think background noise will be loud enough to interfere.

Terry, East Grinstead, UK

Reply to
Terry Pinnell

FFT it to see what the main frequencies are. Notch filter, but beware frequency change if it slows.

NT

Reply to
tabbypurr

the sound unlubricated of plastic gears turning...

Use a phonograph pickup, or a contact microphone, that will get the mechanical noise and exclude most ambient.

but there's other ways too.

maybe it emits magnetic waves when it switches? crossed coils may be able to determine which way the motor is turning,

Maybe you can connect wires to the battery terminals and detect the current surge as it switches.

Does it pass light through the bore when it's open?

--
  When I tried casting out nines I made a hash of it.
Reply to
Jasen Betts

Interesting idea, which I'll check out back in the shed.

Neat, I'll pursue that, although it may involve drilling a hole in the case.

Thanks Jasen, yes, indeed it does, that's a bit of lateral thinking I'd missed!

Probably won't adopt that method though. Getting a consistent light source wouldn't be easy unless I increased its bulk by enclosing it in a light-proof case. And batter current usage would probably be significant.

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New thought. If I'm using it indoors I can remove the case back, giving these advantages:

- power it via an old charger, recovering the large space currently taken by batteries.

- avoids the issue of external access.

Terry, East Grinstead, UK

Reply to
Terry Pinnell

fit an LED into one hose fitting and a light sensor into the other but first paint the insides of the fittings black you could use an infrared led pulsed at 38kHz. Low power seeing as you only need 100mm range and an off-the-shelf 38kHz infrared detector

an off-the-shelf ifrared barrier might even do the trick with some physical modifications. You'd need to upgrade the relay if you want to switch mains appliances.

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  When I tried casting out nines I made a hash of it.
Reply to
Jasen Betts

What about detecting the pressure in the output line? I know pressure sensors exist that will do this. Any idea of the output pressure?

Rick C.

Tesla referral code -

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Reply to
gnuarm.deletethisbit

Jasen: Come late Spring it continues in service as irrigation unit!

Rick: "... a timer for other indoor purposes during the rest of the year."

Terry, East Grinstead, UK

Reply to
Terry Pinnell

There is nothing in your reply that invalidates my suggestion.

Give it a little thought.

Rick C.

Tesla referral code +

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Reply to
gnuarm.deletethisbit

He wants to use it as a timer when fluid is NOT passing through it during the rest of the year - thus no pressure to sense.

Ed

Reply to
ehsjr

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