Acoustic Door Closer




Make your life easier with a door that closes with the right amount of sound. In our Engineering Design class we are currently working on a project where we have to design a smart product that uses sensors. Our group came up with the idea to use a sound impact sensor that can detect sounds to close a door. The idea is for the sensor to detect sounds and the door will close. The main application for this product is in a classroom setting, but it also has multiple other uses. The main purpose is for teachers to use when teaching a class with the door open. Teachers have to stop teaching when the hallway is suddenly filled with noisy students to walk across the room and shut the door. No longer will they have to stop class to close the door, the door will now close own its own when noisy students fill the hall.

Step 1: Materials

-1 9 Battery
-1 9v Hobby Motor
- Screws
-1 Plastic Wheel from Parallax item #721-00001
-1 HomeWork Board from Parallax item #555-28188
-1 Sound Impact Sensor from Parallax item #29132
-1 Solderless Breadboard from Parallax item #700-00078
-1 H-Bridge from Parallax item #603-00019
-2 Alligator Clips from Radioshack item #270-378
-Jumper wires from Parallax item #800-00016
-Spool of Wire from Home Depot (For wiring the sensor through the door frame and the wiring too long for the jumper wires.)
-Basic Stamp Editor v2.5.3
-2 L Brackets from any hardware store.
We also used various sizes of wood, but that is for our model door.
The motor listed above meant for our scaled down model door and will not likely work on the bigger or heavier doors, but may work on normal doors that are light weight. For the bigger and heavier doors you might want to use a motor with more power and maybe a bigger wheel.

Step 2: Designing a Model Door

First, we designed and created a scaled down model door. The model needed to be scaled down because we are only using a little hobby motor for power. The door has slanted sides so it can stand up on its own.

Step 3: Drill a Hole

Drill a hole through the door frame. The hole is for passing wires through to connect the Sound Impact Sensor with the HomeWork Board and Breadboard. You can use a smaller hole size if you want, we just used this size because it's what we had to work with.

Step 4: Soldering

You need to solder the the prongs of the Sound Sensor to three different wires. These are the wires that will pass through the hole in the frame. Without soldering the sensor would need to be attached to the homework board.

Step 5: Wiring

This is how we wired our sensor to the homework board and the breadboard. The diagram shows the same thing, but more organized and easier to read. This is where we used the H-bridge that allowed use to control the motor.

Step 6: Coding

' {$STAMP BS2}
' {$PBASIC 2.5}
PAUSE 1000

FOR move = 1 TO 10
PWM 2,0,100

This is the code for the sound sensor to detect any sounds loud enough to set it off. When the sound sensor is set off it will activate the motor and cause the door to close. Depending on the size of the door you will need to adjust the code to run the motor longer or shorter so it can fully close the door. To adjust the range the sound sensor will detect sound at just turn the knob on the sensor accordingly.

Step 7: Frame

Now we need to build the frame that the wheel will run on to close the door. You need to attach a piece of wood that is about the length of the door to the door frame. You then need a flexible piece of wood that will bend from the attached piece of wood to the other side of the door frame. You will also need to attach the wheel and motor to the top of the door with L brackets so it can run along the frame. There needs to be as little resistance as possible between the wheel and the frame because if their is a lot of resistance the motor won't turn. You will also need to hit the reset button on the homework board after the door closes because it is programmed only to close once so that the motor isn't spinning for every loud noise it detects.



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    21 Discussions

    Kool, albeit a bit complex mechanically. The Spring-Loaded idea mentioned would seem preferable - a door that"wants" to close when not held open. Thus releasing the "catch" allows gravity or spring(s) to effect the desired result.

    Now, I have the opposite problem and thought your team may have hit upon or come across a solution when designing this door project.

    I have a small wire "door" that I want to open thirty minutes (or so - 15-30 would do) after it is shut/closed.

    The circuit should be battery-powered. The Battery(ies) should not be connected to the circuit unless the door is shut and the timer functioning. That is, when the door latch is released and the door springs open, the power should be removed from the circuit.

    I'm not an electronics guy but can bread board a circuit using discreet components and can solder things together if they're not too small!

    2 replies

    Reply 6 years ago on Introduction

    Have you thought about using the spring to open the door? A timer based on a 555 would pull a low-voltage solenoid-activated pin that keeps a spring compressed. The pin would also disconnect the battery from the timer until you reset it.The solenoid could be made by wrapping bell wire around a nail, whose magnetism would pull a small piece of steel toward it. Total cost could be well under $5, including the battery and container. Should you wish, the spring force can be dampened with a small squeeze bottle filled with air. The size of the hole allowing the air to escape by the spring flattening it would determine the length of time it took for the door to open.


    Reply 6 years ago on Introduction

    Yes, that is exactly what I am planning to do. Mechanically, a spring-loaded "door" that is held in the closed position by a latching mechanism that can be released with an electronic pulse as with a solenoid. My idea was to connect the power to the circuit in such a manner as to disconnect the power source from the circuit as the "door" swings open. After all, as the circuit is only there to release the latch so as to open the "door," there would be no need to power it if the door was open. This "cut power to circuit" function would be mechanical.

    Basically I need a circuit that can run off six or eight AA cells that will energize a solenoid with all available voltage fifteen minutes or so after the circuit's "Start Countdown" button is pressed. Know of a source for such a circuit diagram?


    6 years ago on Step 7

    Couldn't you mount the motor and wheel to the door so that the wheel contacts the floor. This would eliminate the need for the rigging at the top of the door and perhaps lower the cost of the system slightly.

    1 reply

    "so that the wheel contacts the floor." Good Catch. Done with unlimited funds and/or access to any tools/tooling necessary, the motor and drive wheel could be fit into the door itself with a tension spring behind the assembly to maintain the necessary contact with the floor. But small wheels running on dirty dusty floors can collect more obstructive crap than a large wheel so, cleanliness would be important.


    6 years ago on Introduction

    Wouldn't it be better if the schematic also used a Homework board instead of an Arduino? Otherwise I like the idea.

    2 replies

    Reply 6 years ago on Introduction

    We didn't actually use an Arduino. Our teacher had us make this project out of parts from our Boe-Bot, therefore we used a Board of Education. We just followed the wiring diagram used for the H-bridge that was done on an Arduino.

    Trike Lover

    6 years ago on Introduction

    The Electric Door

    Wow. A blast from the past.

    I'll relate this just to show that there's more than one way to skin a cat (what a terrible expression!)

    About 1970, I built a sound-triggered electric door opener-closer for my bedroom door. My approach was somewhat different as it depended on what a 13 year old could scrounge. The motor was a sealed-gearbox, very geared-down shaded-pole unit that came from a junked Timex watch display. The output shaft speed was only a few RPM.

    I used a bored out rubber stopper from the school chemistry lab to slip over the shaft, then using steel 2-part epoxy I attached an aluminum flat bar arm about 6 inches long to the flat top of the stopper. A second slightly longer piece of flat bar pivoted on a bolt with plastic washers (margarine container lid cutouts) at the end of the first arm. The rubber stopper acted as both a "slipping clutch" in case the door jammed, and as a shock absorber as the door hit the limit switches at each end of its travel.

    The far end of the second pivot arm attached to a pivot bracket on the backside of the door; the motor was attached to the wall with L brackets. The motor only turned in one direction, so the bend-in-the-middle bell-crank linkage was needed to give both opening and closing motion.

    Limit switches at each end of the "open" and "closed" position were momentary contact pushbuttons from Radio Shack. The motor control system was a series of relays that would operate the motor, stop it when a limit switch was reached, then (and this was the hard part) self-reset. Most of the relays came from the junk pile at the engineering department of a nearby university - no two the same. The voice/sound control was provided by a microphone and transistor on/off switch ordered from Edmund Scientific. That was the only "electronic" component, everything else was electromechanical.

    It took a bit of fiddling to get the bellcrank arm lengths right so that the door would fully close or fully open. The relay power supply - 12-14 volts - came from an audio transformer that had been inside an old hi-fi set. I hooked it up backwards to 120 VAC and it gave (by pure luck) about the right voltage to operate the relay coils. Being ignorant, I didn't know you weren't supposed to do that. :-)

    I remember that making the logic circuit completely automatic using only relays and momentary switches was an absolute stinker of a problem - I worked on it for months. Eventually, it all worked, much to everyone's amazement, including my parents.

    Once everything was in place, it operated for the next seven years without any further service, or having the power turned on or off. The door would open on a loud noise (clap or loud word), and stop in the open position. A second microphone in parallel, inside the bedroom, would actuate the circuit again to close the door. I added a pair of pushbuttons on the bedside table which triggered the circuit the same way. It was amazingly quiet and reliable, built completely from junk, and except for the mail-order "sound switch", a whole set of logic circuits made from electromechanical parts.

    I was about 13 - I built it because nobody told me it impossible (some did later, except I'd built it and proved them wrong), and I wanted an electric door closer on my bedroom. It was inspired by Star Trek, I think. I later went on to study Electrical Engineering, and spent a good many years in grad school and then as a full-time researcher - my "tuition" in homebrewing paid off, I guess.

    Nowadays, the whole thing could be controlled with a couple of op-amps and a MOSFET, or an Arduino. The bell-crank motor mechanism was a good deal more compact than what you've designed (although yours is an elegant design), and it didn't require a curved track - it just tucked in next to the door hinge. The electromechanical logic circuits that ran it all fit in a wooden case about the size of a shoebox, with vents for cooling. All the random small metal parts were also from junk - brackets, bolts, etc.

    The only money expended was for the Edmund Scientific sound switch - about $5.00 - and the cost of the momentary contact switches - about 99 cents a pair. A small square of rubber weatherstripping glued to the door where the limit switches hit softened the impact on the switches.

    I had originally tried magnetic reed switches and magnets - I found a PC board with about 30 reed switches on it for $1 at the army surplus store, but they were unreliable - didn't have the superior magnets available now. I also forgot to mention that I removed the latch bolt from the doorknob set - leaving the knobs, but no latch.

    Thanks for the interesting Instructable, and for the trip down memory lane.

    3 replies

    No problem, we're glad to have reminded you of any fun memories from the past. We had a lot of fun working on this product as well. Thank you for all the information about your door mechanism.

    DoItOrDieTrike Lover

    Reply 6 years ago on Introduction

    One of my favorite devices for opening-closing doors was a BBQ grill motor. They were everywhere (esp. at garage sales) and cheap, often free. High torque at low rpm. They were also good for things like lowering a projection screen or opening a cabinet door or a drawer.

    Trike LoverDoItOrDie

    Reply 6 years ago on Introduction

    Yes, they're great, especially the 120 VAC ones. Never tried to do anything serious with a battery-driven one. I think the watch display motor and gearbox were exactly the same type as are in those BBQ rotisserie motors. I keep an eye out for any I can find. With that square shaft socket on the gearbox, they're incredibly versatile for all sorts of projects.


    6 years ago on Step 6

    you should add a magnetic reed switch to the top of the door to check whether or not the door is open. this would avoid damage to the motor if i tried to shut a closed door. it would also fix the problem of needing to rest it every time

    1 reply

    Thanks for your feedback. We never thought of the idea of using a magnetic reed switch. This was just a fast in-class project that had to be done in a two week period.

    I think this would also work great for people who live on a noisy street, like I do. On weekends, I like to open my window. This would be great for the mornings when the traffic kicks up!

    1 reply

    6 years ago on Introduction

    Did your group consider a spring loaded door with a triggered electromechanical or electromagnetic release? Also, would this also close the door with the sound of a fire alarm?

    2 replies

    Yes, we did, but to keep the budget low, we waived the spring loaded door idea. We made this in about two weeks in the course of a few nights for our Engineering class in High School. The electromagnetic release was never thought of, but thanks, the door will shut from the sound of a fire alarm, if sound is detected, it will shut.


    Reply 6 years ago on Introduction

    This is a much safer idea. Especially if all you want to do is close the door. Just use a normal, well-engineered door closing mechanism and a magnetic catch. The door closes itself when power to the magnetic catch is released.

    The sensor part could easily interface to the catch to trigger it's release.

    How doors open and close in a space being used by the public is something to be very careful about. Especially when you're talking about using motors to force the movement. You don't want to have someone that's unfamiliar with the setup to suddenly get injured because of it.

    Not that it isn't a cool idea, it is.


    6 years ago on Step 4

    you better invest in some thinner solder... 0.7 - 0.5 mm should do