Introduction: Draw Minty Electronic Music

This is taking a previous breadboard experiment and installing it in an Altoids tin.

Along the way I include a few tips about soldering.

A few things different from the breadboard project:
I used a toggle switch instead of a slider.

I added an LED so that you could tell if the power is on.  This is important because this unit is portable and operates on battery instead of a steady power supply.  If the LED goes dim you will want to replace the battery.  The downside to using a battery is that the sound will change pitch as the battery weakens.

All the connections are permanently soldered.

The components are hot-glued to secure them and to insulate them from shorting on other components and the side of the tin.

You may want longer probe wires so you can stretch across larger drawings.

Parts Needed:

Power supply (a 9 volt battery and connector)
Wires (an assortment of sizes with the ends trimmed bare and tinned would help)
Small Switch (on-off or on-on will work fine)
Speaker 16 Ohm 25 W (Actually just about any little old speaker will work)
Audio Transformer (you can pick one up at Radio Shack for about $3) [Model: EI-19 Catalog #: 273-1380, Frequency response: 300Hz to 10kHz, 1,000-ohm center-tapped primary, 8-ohm secondary, Low-level impedance matching]
Transistor 2N3904
Capacitor Ceramic 0.047uF
Resistor 10K
Resistor 3.3K
Paper (a nice piece of card stock would be nice)
No 2 Pencil

For so many of my projects I scavenge my parts from old electronics that are worn out.  That saves a tiny fortune on parts but the cost of most of these parts brand new is probably under $10 especially if you order from a place like
I was disappointed they didn't have the Audio Transformer but I did look it up and found it available at Radio Shack.

Step 1: Prepare for the Speaker

Use a pencil to trace around the speaker on the back of the tin where you want to put the speaker.

The pencil is lightly visible and easily cleaned off of the tin when you are finished.

Step 2: Make a Drilling Guide

Use a block of plywood and drill holes in five rows of five spread across a square inch.  leave enough space on the side so that it places the holes approximately where you want to drill them on the tin.

Lightly clamp the tin between blocks of plywood.  Make sure the holes are lined up precisely where you want them on the back of the tin.

Step 3: Drill the Speaker Holes

The holes will allow the sound waves to travel out of the box without being muffled.

My example shows using a hand-drill but it would be much easier to use a drill press (sadly mine is not working).

Set the length of the drill bit so that it only cuts through the back of the tin and not through the lid on the other side.  Then carefully drill through the pilot holes into the back of the tin.  Do apply too much force on the bit, you don't want to bend the back of the tin.

Once the holes are all cut use a grinding bit to smooth the metal burs from the holes.  If you don't they will tear into the speaker.

Step 4: The PC Board

Find a thin sheet of plastic suitable for a PC board.  (Or you could buy a proto-board and cut and drill it to fit the parts).

Plan the layout of the components from the schematic.  Make an exact size diagram so that you can trace the parts and make sure they will fit in the tin.  Plan the holes so that components share a common hole where they connect to each other.  When you have finished your diagram measure out and cut a small rectangular strip to fit all the components to the diagram.  Make the rectangle a little larger than you need in case you need to make adjustments.  You will snip off the excess when you finally pack the contents into the tin.

Use a pencil to mark where the holes need to go on the plastic rectangle.

The heat from drilling will melt the plastic.  To clean off the plastic simply grind it off the side on a chunk of wood.  Don't press too hard on the side of the bit or it may break.  Only have as much bit exposed as you need.  The shorter the bit the less likely it will snap off.  Try to keep the bit cleaned off for each hole or you will begin to make larger and larger holes as the plastic builds up.

I used a very tiny, wire thin, drill bit and attached it to my dremmel to make precise holes.  I carefully used the bit to cut slots for the mounting posts of the audio transformer.

Step 5: Prepare to Mount Components on the Side

Plan where you want to arrange the switch, power LED, and hole for the probe wires.  

I simply used and extra LED mount for the probes to poke through.  This keeps the edge of the tin from wearing and cutting the probe wires.

Use a sharpie marker to draw the holes on the side of the tin.  Make sure there is room on the inside between parts for the back of your toggle switch and be sure there is room for the Cover to close properly.

Next use a nail or a screw and lightly tap a dent in the center of the holes.  This will act as a pilot so the drill bit doesn't slide across the metal surface.  Because you are making a dent in the side the tension from the small width helps keep the side from crumpling from the tiny impact.  Otherwise I would suggest using a wooden guide to pilot the holes like I did for the speaker.  Plus there are fewer holes and they are spread farther apart.

To determine the size of the holes you may measure the hole in the washers, or use a ruler to measure the diameter of the post.  If you special order the parts they usually have specs you can read to determine the size.

Personally I selected the closest drill bit under the size and then used a dremmel to grind the holes until they were the right size.

Once everything is in place double check to see how everything will fit inside the tin.  Notice I don't actually install the switch until later.

Step 6: Put the LED in Its Surface Mount

From the outside of the hole slide the LED through.  From the other side slide the plastic wire holder into place until it fits tight.  Make sure the longer lead is on the side of the switch.  The longer lead of an LED is the positive side and goes to the positive end of the circuit.  

If you are using parts from an old electronic device the leads may be the same size.  To determine the polarity of the LED examine it closely.  There is a large portion of metal inside, what appears to be a gap, and then a small portion of metal.  The larger side is the negative side and the smaller is positive.

Once the leads are through the holes and the LED is pushed in all the way you may bend the leads over and this will be enough to hold the LED in place.  Later you can add hot-glue  over the terminals if you like at the end of the project.

Step 7: Add Components to the PC Board

First add the smaller components to the board.  Using the diagram determine which leads go together through a common hole.

Find the connections which will have no additional leads or wires added.  Twist those leads together if you can.  Bending the leads outward a bit will help hold them in place until you can solder them.

Step 8: Add the Audio Transformer to the Board

Make sure the wires of the transformer are trimmed so the casing is down to the level where they will touch the surface of the board.  The wires/leads should be long enough to extend through the board just like all the other components.

To secure the transformer in place you may bend over the mounting posts on the sides of the transformer.  Be sure there the wire holes are still big enough to add the rest of the connecting wires.

Step 9: Solder Connections to the Board

Solder the connections where no additional wires will be added.

This is where things can get tricky.

You have to be fairly precise with you soldering.  Try not to touch the board because it will melt to the tip of your soldering iron.  Also don't linger too long on the components or it will melt the board.  Be generous with your flux because it will cause a larger dot of solder to form over the wires which will help secure the parts on the board.  Don't let too much solder flow on the connection because you don't want it to flow between connections and short with other parts.  Also be sure your welds are solid or things will fall apart and the connections won't work.  Make sure you trim off the excess wire because there is limited space in the tin and you don't want wires poking through and shorting on the cover of the tin.

Step 10: Tinning Wire Tips

Tips on tips:
For easier and better outcome it may help to "tin" the ends of your wires.  Then it will be easier to push them through next to other leads without bending or fraying.

Typical wires you may be using will be made up of several strands of wire (unless you use telephone wire).  When you trim the end bare the strands tend to get unruly.

Simply twist the end so the strands are together.

Now dab a bit of flux on the end.

You may touch the iron to the end of your coil of solder an then to the wire or you may use a thin strand of solder and touch the wire with it at the same time as with the iron.  The flux will melt and the solder will rush onto the wire as the flux burns away.  You should only put on enough solder to lightly coat the end of the wire with a shiny silver surface.  The flux on the wire in my example is a bit of and exaggeration.

Step 11: Connecting the Negative

The negative battery wire and the wire that will go to the negative end of the LED should be fed through the hole with the transistor lead farthest from the transformer.

Then they should be fused together with solder.

Step 12: Resistor and Wires on the Switch

Make sure you carefully follow the diagram when adding the 1K resistor to the switch.  This is going to connect to the LED which can only be wired a certain direction.  Plus you want this switch to properly turn the power on and off.  If you solder the ends to the wrong terminals the unit will not work.

The toggle switch I am using actually has six posts even though from this angle you can only see three.  I am only using two posts.  In my example the power connects to the middle and distributes to the outer post when the switch is on.

Connect the other end of the outside wire to the center wire on the Primary side of the Audio Transformer.

Step 13: Add the Probe Wires

The pictures show that the red wire from the switch is actually connected to the top of the board because I had trouble feeding it through the middle hole on the primary side of the transformer.

Now the probe wires are fed through and connected.

Step 14: Connect the Long Lead of the LED

Next carefully trim the long lead on the LED and the 1K resistor and solder them together.  Make sure you trim the excess off leads as you go through this project.

Step 15: Negative Wire to the LED

Carefully manage the wires as you go.

Connect the negative LED wire from the board (Connected with the Negative battery wire).

Step 16: Connect the Speaker Wires

Put the speaker in position and attach the wires to the two leads on the Secondary side of the Audio Transformer.

Step 17: Ready for a Test

Now fit everything in place.  (Notice the battery I had been using was already old and had to be changed out).

Trim the excess plastic off the PC board to help it fit.

Switch on the power and make sure everything is connected properly and works.

Step 18: Finishing Touches

Now get the hot-glue gun out and warming up.

Takes some electrical tape and make a blanket to cover the back of the board to prevent it from touching the cover when it closes.

Make sure the wires are all trimmed properly.  Put hot glue over the solder points and secure the electrical tape over the hot glue.

Lastly hot glue the outer edge of the speaker so it doesn't rattle around in the tin.

Close everything up and enjoy your new creation.

Step 19: Conclusion

Thanks for following along with this tutorial.  Hopefully it made enough sense for you to figure everything out.

I am very well pleased with the outcome.  I never dreamed it would turn out so nicely.  Other than having to rethink the layout a few times everything seemed fairly simple.

In order to hear the sound better you should actually flip the unit over so the speaker is face up.  If you do this project please let me know.  I'd love to see your results!  It would be great to see what drawings you set to electronic music.

Check out my Youtube Demo if you get a chance, it will give you an idea of what you can do next with this unit once it is complete.

Step 20: Modifications

I've added this step because there are some really fun directions you can take this project.  Here is a MOD (modification) you can incorporate into the project.  If you are clever you may even be able to build it into the box.

The principle of the project operates on the use of a variable resistor in the graphite on a piece of paper.  So one fun mod you can do is add a variable resistor (50k potentiometer) and a momentary button (switch).  Now you can control the pitch with the knob and initiate the sound by pushing the button.  With a little practice you can even play a tune (almost like playing a sliding trombone).

If anyone does this project please post a comment with a link to your pictures.  Also if you have a cool mod post it here as well.

Have fun making some minty music!

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