Make a Sound Tube (message in a Bottle)




Introduction: Make a Sound Tube (message in a Bottle)

A sound tube is a very intuitive gadget: Make a sound in one end of the tube. Close it to store the sound inside the tube. Release the sound by opening the tube's other end.

To indicate that a message is waiting to be released, a string of leds lights up when the tube is put down vertically, with the speaker-side up. When the speaker-side is down, the leds are off.

My first idea was to make a Sound Jar with just one opening, the jars' lid. Open the jar, make a sound into the jar and close it. The stored sound should be set free when opening the jar again. Making that work turned out to be a little tricky for me. So I made the jar into a tube, which simplified the electronics a lot.

We use our new Sound Tube as a message container, replacing the notes on the kitchen table to tell family members our whereabouts and yes, they can have some cookies. Other kinds of use can be seen in the video...

No video playing? Have a look at it here...

The Sound Tube works really well and it is very intuitive in it's use. Picture 3 in this step is a sketch of the upcoming Sound Tube version 2.0. Idea is to stick together two funnels to get the shape in the sketch. Or 3D-print the whole casing in one time...

If anyone has thoughts on how to turn this Sound Tube into a real Sound Jar with just one lid to open (even more intuitive!?), please let me know :-)

Making this Sound Tube is not very difficult. The heart of the machine is a hacked voicerecorder, that can be bought at various spots. The circuit that makes the leds blink is very basic and well doable for starters in electronics and soldering (although some precision-soldering was required at one point with my particular voicerecorder). When you have the stuff needed, the Sound Tube can be made in a couple of hours, I think. Have fun!

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Step 1: Stuff You Need

The heart of the Sound Tube is a voicerecorder: A nifty circuit with a microphone, a speaker and two push-buttons attached to it. These voicerecorders are available in various types. I bought mine at for €15,- in february 2011. The voicerecorder on the picture is a much easier model to use for this Sound Tube

For the tube and the lids, I used a cardboard tube (outer diam 74 mm) used for sending posters and the like by mail. I bought it at an art supply store.

Everything on the list will set you back around $30,-, if you have to buy it. Chances are that most of it is in your shed somewhere...
Here's the complete list...

For the electronics (everything is available through (for Euros), Velleman (North America) and Farnell (Australia and Europe):
  • 6 low current led's, pick a color.
  • NE555 timer ic
  • a "roller ball switch" or tilt switch
  • Electrolytic capacitors: 100 uF and 22 uF
  • Ceramic capacitor: 0,01 uF
  • Resistors: 390 Ohm, 1 kOhm and 56 kOhm
  • 2 microswitches
  • A voicerecorder. The one in the picture is perfect for the goal, because the two push-buttons can be replaced very easily. My voicerecorder had one push-button on the pcb, which was tricky to attach to a microswitch.
  • Some supple wire
  • A pre-etched pcb with copper rows
  • Jumper wire
  • 9 Volt battery with connector
  • a small switch that can be mounted on a pcb board

For mounting the electronics:
  • Tie raps in various sizes
  • 5mm plywood, or a sheet of hard plastic (ABS, acrylic glass or PVC)
  • Glue
  • Bolts and nuts and washers, size M3 or so

For the tube:
  • Cardboard tube diameter 74 mm with two lids that fit pretty tightly into the tube

Tools needed:
  • Soldering gun (and solder, and desolder of course...)
  • Third hand
  • Pliers
  • Powerdrill and a 4 mm drillbit
  • Sharp knife
  • Glue suitable for fixing wood and plastics

Step 2: Hacking the Voicerecorder Circuit

The voicerecorder circuit involves two pushbuttons: One to activate the recording of sound via the mic, another pushbutton to play back the recorded sound through the speaker.

Replace the pushbuttons with microswitches. Keep in mind that the microswitches must CLOSE the circuit when the tube is OPENED, so be sure which lead to attach to the wires. If you're in doubt, use a multimeter to check which leads to use.

If you're lucky, you can just cut the pushbuttons' wires and solder the microswitch directly in the spot where the pushbutton was.

If you're not so lucky, the voicerecorder has an on-board pushbutton (like mine). You'll have to do some micro-skill soldering to attach a microswitch to that spot. Solder two leads to the microswitch first, and then solder the leads ends onto the pcb pushbutton circuit. See picture 3 for how to do that.

Step 3: Build the LED Circuit (with Tilt Switch)

A string of LEDs... (pictures 1, 2, 3)
The six leds in the tube are connected parallel (all the led's plus-sides are connected, and all the minus-sides too). Use stranded (supple) wire to connect the leds, so they fit into the tube nicely later on. To connect the leds to eachother, I soldered 6 strings of wire pigtail, and then soldered the pigtails onto the led's leads. See picture 3 on how to do that. If it's not clear to you then, have a look here for a more detailed explanation...

Blinking LED circuit (pics 4 through 8)
The circuit that makes the leds blink (picture 4) is a very basic circuit around a 555 timer. This is not the most efficient way to do the job, because the 555 timer consumes a fair amount of energy just to stay alive. I used this scheme just because I had the soldered pcb lying around (it is a remnant from a previous I'ble I made). On the pcb a switch was soldered already. I replaced this switch with a roller ball switch.

This circuit should be turned on when the Sound Tube is set vertically, with the speaker-side up. A roller ball switch (or a tilt switch) takes care of this. 
  • Solder the components onto a pre-etched pcb. Cut the copper strips where marked with an X in the drawing (picture 5).
  • Solder pieces of supple wire of about 8 cm (3") to the roller ball switch' leads.
  • Eventually, solder the string of six leds to the pcb and test the circuit.
I tried to make a roller ball switch myself, but the attempt failed miserably. See pictures 10 through 15. None of these switches work :-s

Powering the circuits
The voicerecorder and the led-blinking circuit are powered by the same 9 Volt battery.
I made a seperate, small pcb on which the battery's leads and a switch are mounted. The powerleads to and from the voicerecorder and led-blinking circuit are all connected to this pcb.
The switch is used only to shut down the Sound Tube completely.

Optional (picture 9): Leds fading in and out
What I really wanted was an array of leds that fades in and out. I spend hours trying different kinds of circuits, but none of them worked the way I wanted to. Making a led fade in was not so hard, but letting a led fade in and out without a microcontroller is truly a tricky task to accomplish...
Eventually, I got help from Jan Leisink, probably the best science teacher in The Netherlands. He came up with a circuit that almost worked the way I was looking for. After some tweaking, I got it right. Unfortunately, that was after the Epilog Challenge deadline, so that's why it's not in the Sound Tube I made.

Now, if you build the circuit in pic 9, chances are that it will not work just as you expected: The way the leds fade in and out depends strongly on the values / specs of four components in the lower left side of the circuit: The leds, the transistor, the capacitor and resistors. To make tweaking more easy, I put a variable resistor in the circuit. Adjusting it's value influences the way the leds fade in and out.

A big advantage of this fade-in fade-out circuit is that it is much more efficient in energy than the 555-timer circuit. So using this circuit will make the 9V battery last a fair bit longer. Give it a try, if you like.

Step 4: Mounting the Pcb's

You're done with the electronics now, but everything needs to be mounted inside the tube to make it a decent Sound Tube.

Cut a piece of plywood. The size of this board depends on the size of your tube and the height of the lids. The board should fit as closely as possible in the closed tube, leaving only 5 mm from the small sides of the board to the lower part of the lids. My board measures 6 x 15 cm (4" x 6").

Also cut pieces of plywood with the same curve as the inner diameter of the tube. These curved pieces act as a support, and are needed to fix the board later on. See pictures 4 and 5. I glued the supports under the plywood board.

  • All the parts (pcb's, battery, microswitches and roller ball switch) are mounted on the rectangular piece of plywood using tie raps.
  • This is also the moment to determine the direction of the roller ball switch: The leds should light up when the tube is set down with the speaker side up!
  • The microswitches should be at the very top and very bottom of the plywood board. Again, I used tie raps to fix them onto the plywood board.
  • Before fixing the parts, lay out everything to make sure that it fits (picture 2). If necessary, adjust the length of the wires connecting the parts (picture 1).
  • Drill holes around the parts that will get a tie rap around them (so, mark the spots where holes should be drilled, remove the parts from the board, and then drill the holes)
  • Because I didn't have space available on the pcb for the roller ball switch, I mounted it separately on the plywood board, using another tie rap. See picture 3.
Test the board again! Everything should work properly now: When the board is turned over, leds should blink or stop blinking. The microswitches should switch on the recording function and the loudspeaker (push down one switch while testing the other. My voicerecorder acts funny if both switches are closed / when both the recording and playback functions are on).

Step 5: Preparing the Tube

With picture 1:
The lids for my cardboard tube fitted VERY tightly. To make it a bit easier to remove the lids and to put them back, I sanded the rims of the lids and the inside of the tube. It took me a while to get it just right.

With pictures 2 and 3:
To fix  the leds into the tube, you'll have to choose now what the "speaker-side" of the tube will be. Drill six holes, (diameter 4 mm, a little bit less than the diameter if the leds) spread evenly over the circumference of the tube. Drill the holes about 4 cm under the rim of the tube. Beware: The leds should be just above or just below the curved supports under the plywood board. Check this before you start drilling!

Step 6: Final Assembly and Finish Up

Final step, almost done!

Now is the time to get the board with electronics and the lcd-array into the tube simultaneously.

Start by pushing the leds through the holes in the tube, from the inside out. Then, hope that the leads from the leds to the pcb are long enough, and shove the plywood board with electronics into the tube. Be careful not to pull out the leds out of their holes in the tube...

Lock the board with bolts and nuts (picture 1)
When everything is put inside, center the plywood board in the tube so that the distance from the rim of the tube to the closest side of the board is the same on both ends.
Now drill 4mm holes in the tube just outside the curved supports of the plywood board. Stick M3 bolts with a washer through the holes and fix them with a washer and nut on the inside. Now, the plywood board cant move in the direction of the tube anymore, and the board will stay oin place when the lids are pushed against the microswitches...

So, now, you're done really. I wrapped a sort of colored label around the tube (used spray glue to fix it). I'm not very fond of the result, however. So your decoration of the Dound Tube will be at least as good as mine...

Enjoy, and thanks for reading!

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    42 Discussions


    5 years ago on Step 3

    An alternative circuit is a straightforward a-stable using the 7555 (actually, you gave me that idea, used it for a blfnar). A very nice setup is to put 6 LED's anti-parallel and put a decent sized capacitor in series. if you then also put a resistor parallel *) to the LED's it ensures the full (dis)charge of the cap. Whenever the 7555 flips, 3 LED's will flash on, fade out. Very nice effect.

    *) you best size the resistor that multiplied by the value of the series capacitor is roughly the same as the R*C of the 7555.


    Reply 5 years ago on Step 3

    Sounds interesting... What do you mean by "anti-parallel"? Could you draw a circuit to explain?


    Reply 5 years ago on Step 3

    See image, sorry for the quality, draw in yoh-draw ;-)

    The idea is if 3 goes high, current rushes through the top 3 LEDs. As the C charges, the current will fade away. The LEDs will be off under about 1.6 V at which point the resistor will ensure the capacitor is fully charged. When the 3 goes low, the capacitor discharges over the bottom 3 LEDs and again the resistor will ensure a full discharge.

    The resistor is needed if that last 1.5 V is really needed. It is when powering from a 3V source. If you stick with say a 9 V battery, no need at all as the C will charge to 7.5V (battery minus LED forward voltage).

    I would recommend a small current limiting resistor in series with the C, though the 7555 can be mishandled somewhat.


    Reply 5 years ago on Step 3

    Cool! All clear, thanks!


    Reply 6 years ago on Introduction

    Did you notice I made the video on Monster Marit's 11th birthday?


    9 years ago on Introduction

    my jar idea:

    you open the lid of an empty jar (empty is signalled by LEDs or lack thereof) and can then record. This makes the jar full. (signal by LEDs, etc)

    You listen to a recording by opening the jar.

    You empty the jar by turning it over and pouring the sound out. A mercury switch of some sort?

    The only thing I'm not sure about is when to start recording again after emptying. As soon as you turn the jar back upright (makes it unobvious how to leave the jar empty), or should one have to close and open the lid again (awkward to empty the jar and then leave a new message)? :)

    With some bonus LEDs and a counter, could the age of the message be indicated? (it'd be nice to know if there is something new, or if it's the same as the last time you saw the jar... :)


    Reply 8 years ago on Introduction

    Possibly, It would need to have the display (You can find pre-built analog ones at Radio Shack or any hobby shop) and a switch to start the timer (something like a tilt-switch or copper foil on the lid depending on how and when you want the timer to start.)

    Also, have you thought of using an arduino board to control it all. I bought mine in July and it seems like it would work great for something like this.

    Mr. Pyro
    Mr. Pyro

    8 years ago on Introduction

    OR! You could be boring and old fashioned and have a jar full of paper and a pencil that you leave PAPER NOTES in that people TAKE OUT AND READ! and a small flag to signal! wait a minute.... did I just describe a mailbox? -.-


    9 years ago on Introduction

    This is awesome! I have one of those voice recorder things and my fiance and I always leave notes to each other on it. This is way more fun and stylish to have as a decorative piece rather than an exposed board with a bunch of wires hanging out. Great idea!


    9 years ago on Introduction

    Misschien moet je wel voor een volgend project even een boek met citaten doorbladeren. "Zakdoek" is niet meteen een uitspaak waarmee je de geschiedenisboeken gaat halen :P


    Reply 9 years ago on Introduction

    :) Ik bedacht gisteren dat "vloerbedekking" een veel beter woord was geweest. Het fameuze "Hello world" heb ik overwogen, maar vond ik uiteindelijk te afgezaagd...


    9 years ago on Introduction

    now you don`t need paper in a bottle to write an sos mesage in an island


    Reply 9 years ago on Introduction

    Dank je! Waarmee precies?



    Reply 9 years ago on Introduction

    Met het maken van zo'n awesome gadget!
    En ook misschien een beetje omdat dat voorkomt in het filmpje op 0:33.. :D


    Reply 9 years ago on Introduction

    Ah, xnappem! Beetje traag van begrip, vanavond, lange dag gehad :-) thnx!