# Door opened/closed by loud noise? Can I do this?

Thread Starter

#### Rawjcl

Joined Oct 1, 2015
4
I'm wondering if someone can point me towards schematics that might work for part (or all) of my project.

I need an 8 to 32 volt dc motor to switch directions (open and close a shutter/"trapdoor"-type light blocking thing) when a loud noise (vacuum pump) is switched on or off.

The vacuum pump is wired to a count down light switch. It is turned on manually and automatically shuts
off after 20 or 30 minutes.

I'm guessing I'd use a little 1/4 inch mic element or one of those flat piezo discs taped to the vacuum to trigger the motor, 2 whisker micro limit switches to stop the motor when the shutter is fully opened or closed and a few transistors.

Thanks in advance.
Roger

#### mcgyvr

Joined Oct 15, 2009
5,394
sure..
but why not just use a vacuum switch?

#### Dodgydave

Joined Jun 22, 2012
10,050
Why not use a mains powered relay, fed from the vacuum pump to switch the trap door motor on?

Thread Starter

#### Rawjcl

Joined Oct 1, 2015
4
I dont know anything about vacuum switches.Can I get one for $3 or less? Is it something I might salvage from a car at a junk yard? Or what other devices might I salvage one from? Also, I was hoping to spend$15 or less on the whole project, including the trigger and all control circuitry. I already have the DC motor.

I figured my \$15 budget would be possible in my case because there's an electronic surplus store here that sells components for pennies on the dollar.

Oh, one more thing... I did say vacuum pump, but I'm actually using a shop vac right now instead of a vacuum pump.

The vacuum cleaner accomplishes the same thing, but the inside diameter of the hose is 1.5 or 2 inches instead of the tiny hose/tube a vacuum pump would use. How would I hook up a vacuum switch in that situation?

Thanks again for your input.

sure..
but why not just use a vacuum switch?

Thread Starter

#### Rawjcl

Joined Oct 1, 2015
4
I'm trying to avoid mains power. I don't want the possibility of electrocution or fire (now or in the future) if I do something wrong.

But your suggestion sounds like it might work as a trigger to turn the motor on.

But how do I make the motor switch directions to close the door after the power outlet the vacuum is plugged into shuts off?

Thanks.
Roger

Why not use a mains powered relay, fed from the vacuum pump to switch the trap door motor on?

#### Dodgydave

Joined Jun 22, 2012
10,050
You would need a dpdt relay, with limit switches on both sides of the door opening, one for open and one for close, .

#### AnalogKid

Joined Aug 1, 2013
9,351
8-32 V is a wide range. Can you run the motor on something stable like 12 V or 24 V? If so, what is the motor current?

Ebay has a zillion little light sensor and sound sensor relay boards. They all have SPDT relays, so you will need two SPDT relays to switch power to the motor. It might be easier to use a light sensor and just plug a night light into the same outlet as the controlled vacuum pump, rather than try to reliably sense a change in audio or vibration.

Motor power supply (always on)
Sensor board with SPDT relay output
2 SPDT relays, same coil voltage as the motor, *both* contacts rated for the motor starting current
2 limit switches

ak

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