How can I make this white-noise machine switch on when I close a door?

January 1, 2014 10:44 AM

I plan to buy this white-noise generator. I'd like it to be set up so that the machine is positioned outside the door to a room, and when the door is closed, the machine turns on, in order to muffle sound from that room. I am trying to figure out how to set this up. Maybe I could connect the machine to a switch positioned inside the door frame, so that when the door is closed it presses down on the switch?
posted by ElEmigrante to Technology (14 answers total)

Door switches these days are contactless, using magnets, like this one. No wear, no moving parts. The switch-state follows the door state, i.e open is open, closed is closed.

You can put it on the top or open side of the door-- you may be able to put it on the hinge side of the door, but it's a maybe; the switch might close when the door is still somewhat open.

I linked to an online shop, but these are available at your local mega-hardware store, and just possibly your local hole-in-the-wall hardware store.
posted by Sunburnt at 11:17 AM on January 1, 2014

How permanent do you want this to be, and how comfortable are you with electrical circuits? Here's an example of a switch designed to mount into a door frame, but you'll need to do some drilling and sheet rock cutting to install it properly. Note that like most door-activated switches, this one is designed to close a circuit when the door is opened, since usually people use these on closets to automatically turn on the light when you open the door. You can make this work for your situation by using the switch to trigger a "normally closed" relay (or the NC contacts of a SPDT Single Pole Double Throw relay,) powering the white noise generator through the relay's output. (A relay is just a voltage-activated switch that opens or closes its output contacts based on the presence or absence of voltage on its input.)

I would recommend choosing a relay that can be triggered by a low DC voltage that you provide with the output of a wall wart, rather than doing a bunch of homemade high voltage wiring yourself. You'll still need to interrupt the high voltage power cable with the relay output, but you can put all that inside of a grounded metal box. Be careful and aware of your local electrical codes.

On preview: you can certainly use a magnetic switch of the sort Sunburnt suggests and wire it the same way with the relay. You can probably even find a NO switch, but you'll still need the relay to use the low voltage signal from the switch to operate the high voltage white noise machine.
posted by contraption at 11:21 AM on January 1, 2014

Here's a 120v contact door switch, would take a little drilling and chopping to work into a door frame, and unless the documentation for the product states otherwise you want to make sure to make all connections inside an electrical box, but that obviates the additional relay circuit.

It's available in Normally Open, which would close when you closed the door and pressed the plunger in.

I found it by searching for "120v door switch", you may be able to find a magnetic reed switch to do similar (and that would more easily be mounted on the surface), I just didn't dig that far. The particular application appears to be "closet door light switch", except that you want the opposite of that. But it looks like they're available.

Might just find your local contractor's electrical supply house and go ask them for the appropriate version. Most of those places will take cash or a check and sell to individuals if you're nice (in one local case, non-contractors use the side entrance and get second class treatment, but at least we can get the good stuff, which the big box stores don't generally have).
posted by straw at 11:38 AM on January 1, 2014

The problem you're going to run into is that the normal thing to do is to turn on a light when the door is open. The little magnetic switches are great to detect when the door is closed, but they're only suitable for low voltage control circuits, not household AC. You'd need a relay that's rated for AC if you want to cut off the AC power.

I can't tell from that Amazon listing, but does the white noise generator have a wall wart, or does the plug the standard cord you'd see on a lamp or toaster (which means that the transformer is built in to the device)?

If there's a wall wart, you could probably just splice the magnetic switch that sunburnt linked into the power cord and all would work, though you should verify that the switch is rated for however much current the wall wart will be supplying.

If the transformer is inside the device, then you'll need to switch the high-voltage AC, which is more dangerous, especially if you don't know what you're doing with electricity. The safest way to do this would be to make an outlet that is switched based on the state of the door. I'd probably get a metal outlet enclosure, and an off the shelf AC relay. (That enclosure may not be deep enough, so you may need to buy a deeper and/or wider enclosure, and then buy the outlet and faceplates separately.) You can wire the relay to any magnetic switch as shown in the 'normally open' instructions, placing the outlet where the diagram says 'LOAD', and using a three prong cord to plug the whole thing into an existing outlet, making sure to ground the enclosure.

(These are just the first products/suppliers I found when searching.)
posted by yuwtze at 12:26 PM on January 1, 2014

An alternate solution occurs to me belatedly. The device appears to have an switch on the front, which is almost certainly is low-voltage DC. It's a three-position switch, so there would be three wires feeding the switch on the back side. If you're willing to take the device apart, it may be possible to splice the magnetic door switch into the right wire so that the door switch will be a secondary switch, requiring both switches to turn the device on. This probably requires a use of a soldering iron and permanently modifying the device, so depending on your skill level, it may not be something you want to do, but it's probably the route I'd explore first.
posted by yuwtze at 12:50 PM on January 1, 2014

I have that machine; it's a standard cord.
posted by ThePinkSuperhero at 12:50 PM on January 1, 2014

Thanks for the replies so far. I know next to nothing about electronics & electrical circuits, so it sounds like I would either want to hire someone else to do it, or come up with a different solution.
posted by ElEmigrante at 1:34 PM on January 1, 2014

In small shops they often have a door chime that works by bouncing a laser beam back and forth in front of the doorway, so that if someone walks in their body interrupts the beam, causing the chime to sound. Some will just keep sounding continuously if you stop halfway through and stand there. Similar sensors appear to be widely used in home and building security systems.

If you could find one of these that switches power on instead of sounding a chime, you could rig it up so that the laser and sensor are pointing through the open doorway and the beam is broken by the door being closed. You'd just have to position it in the top corner or something like that so that someone walking through the door wouldn't set it off accidentally.
posted by XMLicious at 1:51 PM on January 1, 2014

Can you explain what you are trying to accomplish? Why does this need to be automatic when the door is closed, rather than manually turning it on just before you enter/exit? The best I can guess is that you want this to be installed outside of a bathroom, but not have to explain it to guests, but if you can explain your end-goal, someone may be able to suggest a better alternative.

For example, if you're okay with just sensing when there's motion inside the room, a product like the Belkin Wemo Switch + Motion may work for you. (Disclaimer: I've researched these, but haven't actually bought/used one.) If you set up the motion sensor in the room, and plug the white noise machine into the outlet, you should be able to program it such that the machine comes on any time someone walks into the room, and stays on for X minutes after the motion stops.
posted by yuwtze at 2:46 PM on January 1, 2014

> The device appears to have an switch on the front, which is almost certainly is low-voltage DC.

I disagree that the switch is likely to be low voltage. This "white noise generator" is really just a fan inside a strategically vented enclosure that's been in production since the 1960s, and I really doubt there's any low voltage or logic circuitry in there at all.

I like the motion sensor idea, here's a cheaper and simpler motion-activated outlet that would also work if you don't mind running a cord through the doorway.
posted by contraption at 8:22 PM on January 1, 2014

Just a note about the item contraption linked. I have that; the max it can be set for is 20 min on.
posted by tilde at 12:10 PM on January 2, 2014

tilde, does the outlet turn off after 20 minutes even while somebody is still present and re-triggering the motion sensor? My reading (and the usual way for things like this to work) was that the delay would start after it stopped sensing motion. In any case, now that I look at that listing in greater detail I see that the reviews are not so great. There are a number of similar units available that don't have the conveniently remoted sensor, but you could get around that pretty easily with an extension cord if you don't have a receptacle facing the room occupant(s).
posted by contraption at 2:56 PM on January 2, 2014

> I disagree that the switch is likely to be low voltage.

Yikes, contraption is right. I'd assumed that this was a fancy speaker that played white noise, but now that I read the description more carefully, I see that I'm wrong. If it isn't clear already, taking my suggestion about rewiring the switch is a quick way to create both a shock hazard and a fire hazard. Whatever you do, don't do that!
posted by yuwtze at 5:10 PM on January 3, 2014

Yes, after motion stops; mechanically it might just reset over & over each time it detects movement.

I have the sensor positioned atop a half (1/4, really) wall in a foyer that has stairs leading to the top floor about 15 feet away. Just about anywhere you are in the foyer or room moving (15x20 room) you will trigger it; coming down the stairs to the second landing into the foyer & room you'll usually trigger it from there through the lowest flight of the stairs.

For some reason I read the OP more as like putting the baby down with white noise machine to keep baby asleep or adult napper. Not, "going in there to do stuff & audio block the world" & would keep triggering.

Also- though the item is linked on Amazon, I got it at Lowes so if it doesn't work, easy returns.
posted by tilde at 10:30 PM on January 3, 2014