(Part 3 of 4) Arduino Sampling Drum Pad - Electronics Guide

Lets build some drum pads!

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This is Part 3 of 4 in the guide to Making Arduino Sampling Drum Pads

Part 1: Breadboarding Drum Pads

Part 2: Case Construction Guide

Part 3: Making the Electronics

Part 4: Converting & Uploading Samples

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Populate The Circuit Board

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Overview:  Here we'll add all the components that need to go onto the circuit board.  We'll add them each step-by-step to cut down on any possible mistakes.  

Take your time and follow the pictures closely.  If you make a mistake it's not the end of the world: the board has lots of space even once populated.  If you add a component in the wrong place, you can probably work around your mistake, as long as the correct pins are linked.  If not, de-solder, and then correct the mistake.  

Tip: If you start getting sloppy, or are making lots of mistakes then it's probably time to take a break.

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1.

Here's our starting point.  Take note of the placement of the Arduino in relation to the numbers & letters printed on the blank circuit board.  The pins from one side run from 06-A to 06-O, and the other side 12-A until 12-O.  Note which end the USB connector is facing.

Now's the time to use the optional socket if you're using one.  This will allow you to remove the Arduino easily should you want to re-use it in other projects.  Just make sure you buy one with the correct amount of pins (unlike me).

So, solder all of the pins to the board, making sure that none of the solder bridges between any of the pins.  You can use a multimeter set on 'continuity' (ie it'll beep when you have two parts that are connected) to check this, or use your eyes.  If you do have any bridges, you can use a solder-sucker or wick, or just heat up the area with the iron and try to scrap the offending part away.

Here's a photo of a completed board, just to give you an idea of what we're working towards (note, the connections might not completely match the guide so don't use this as a reference):

And here's the bottom.  Note how sometimes you can use the legs of the components to reach other areas of the board (An example of this is from L-16 to L-12).  This will save you time and solder.

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2.

Add the 1N914 diode, making sure the black line is facing away from the Arduino. When you solder underneath, you can see pin G-5 is also joined to the Arduino pin (G-6).  This should be pretty obvious, so I won't mention these sorts of joins again.  

You can trim down the diode legs once soldered (again, I won't mention this in future parts unless the legs can be useful for bridging).

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3.

Add the 270 Ohm resistor.  Unlike the diode, the resistor can't be put in the wrong way.

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4.

Add the 1M resistor (1 million Ohm).

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5.

Add the 1N914 diode...  Note the position of the black stripe on the diode > it’s important that it faces  the correct direction

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6.

Add the 1k resistor and use one bent leg to reach over & join to the Arduino pin.

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7.

Now we add the 0.1uF capacitor pushed over onto its side so we save on vertical space.  Capacitors often need to be placed in a certain direction (known as polarity), but not this one.  

Solder in the legs (1st image), and then bend them over join (2nd image):

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8.

Now we add a small piece of wire to jump between points;

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9.

...And a bit more wire;

...And that's the board finished.

Populate the Front Panel

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Overview:  First we'll join any wires that are connected to different parts of the panel.  After this we'll add the wires that will then get connected to the circuit board.  We only join to the circuit board once this section is complete because it can be a pain working with both joined together.

Hint: The colour of the cables do not matter, but they do make it easier to identify where they originate from.  If you only have one colour that's fine, but it'll just be harder to trace them if there's a problem.

1.

Here's how your panel should look after adding the components. Note, this is the back of the front panel.  Does that make sense?  Here's a real life image just to confirm:

The Piezo cables should be poking through a small drill-hole in the case, and you should also take into account the LED legs > The shorter should be on the left, the longer on the right.

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2.

Add a wire between the volume & pitch knobs, leave some space on the pitch knob pin, as we'll be adding another wire to it next (you can even hold off soldering this connection until you've added the next wire if you find it easier).

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3.

Before we join the next wire, you need to be sure you're soldering to the correct lug of the audio jack.  We want to join to the ground lug, which is shown in the below picture connected to the black wire.  

Notice how this is joined to the base/center of the audio jack, whereas the lug with the red wire appears not to be joined to anything (it's actually connected to the tallest part of the audio jack, the part where once the heaphone jack is inserted, the tip touches). You can confirm this by using a multimeter.

So now you know which part of the audio jack is ground, connect the wire to it.  Again, try and leave some room, as in the next step we'll be adding a second wire to this connection.

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4.

Now we add another wire from the audio jack.  Eventually this wire will join to the circuit board, so you'll want to make it long enough so we can comfortably work on both the board and the panel.  I'd say 10cm would be perfect.

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5.
 

Run a cable from the volume pot to the positive side of the audio jack;

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6.

Connect a cable from the pitch pot to the bottom for the switch lugs.  We'll be adding another wire to the bottom of the switch next, so be prepared for this.

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7.

Add a 10cm bit of wire from the bottom of the switch.  This will get connected to the circuit board eventually.

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8.

Add a 10cm bit of wire to the centre of the switch.

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9.

Add a 10cm bit of wire to the top of the switch.

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10.

Add a 10cm piece of wire from the Volume pot; 

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11.

Add a 10cm piece of wire from the Pitch pot;

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12.

Now we add a 10cm piece of wire from the shorter leg of the LED.  We never want the metal legs of the LED to touch each other, so you may wish to trim this short leg even shorter to stop this from happening.  You can even cover the joins with heat shrink tubing if you're particularly fussy.  Just make sure you remember which leg was the shorter one.

Tip: joining the wire to a leg can be made easier if you bend each connection into a 'V' shaped hook, hook both parts together, then bend flat to join with pliers, then solder.

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13.

Now finally we add one last piece of 10cm wire...

That's the panel finished, now we just need to join it to the circuit board.

Join The Circuit Board to The Front Panel

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Overview: Now it's time to join the circuit board to the front panel.  Hopefully you've used the advised 10cm pieces of wire, as that will make turning the circuit board over easier.  Not to worry if you haven't, it'll just be slightly more fiddly.  You might notice the two Piezo pieces of wire aren't 10cm... so we'll solder those last.

1.

First we'll join the shorter LED wire to the board:

Join it to the 1k resistor;

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2.

Now for the longer LED leg;

Connect it to the 5v Arduino pin

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3.

Now take the middle pitch wire...

And join to the Arduino;

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4.

Middle Vol wire;

Join to the resistor/capacitor connection

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5.

Take the audio ground wire....

...then join this wire to the other side of the capacitor connection...

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6.

Take the top switch wire;

...Join that to the Arduino GND

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7.

Now the middle switch wire...

...connect here

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8.

Take the bottom switch wire;

...connect with the Arduino 5v

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9.

Now we're nearing the end.  Take the black Piezo wire...

...and join it to the bottom of the board to the diode

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10.

Now finally, take the red Piezo wire...

...and join it to the bottom of the board, the opposite side of the last wire;

We now should have a working drum-pad-thing.  Plug it in and give it a try.

Finishing Up - Fixing the bottom of the case

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Overview: We now just need to add the bottom of the case, and to make sure the Arduino is held securely in place so we can plug in the USB cable.  For that we'll secure it to the MDF bottom using some bolts.

What we'll need:

Our completed case / circuit board

Our 12 x15 cm MDF case bottom

x2 M2 nuts and bolts, they need to be long enough to go through and reach our circuit board, I'll be using m2*19 (that's 2mm wide and 1.9cm long)

x4 Screws for each of the corners.  I'm using M3*12 self tapping screws (you know, sharp ones

x4 Rubber feet (if you want)

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1.

First compare your circuit board to the bottom of the MDF board and draw in some hole markers (in green in the image).  Drill the bottom board with a size 2 drill bit;

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2.

Push though the bolts and secure with the nuts.  Don't over-tighten them so the board flexes.

 

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3.

Now we add screw to each corner.  I'd recommend drilling some guide holes first with a size 2 bit.  After that you can add some rubber feet if you need them, and then we're pretty much finished;