Force Sensor Assembly

Overview 

Gather the materials below and get ready to assemble the force sensor for the piano.

Parts

All Parts
All Parts
Velostat sheet
Copper tape
Solid core wire
Electrical tape
Wood laser cut case
Wood laser cut template piece
M3 female to female spacer 17mm
M3 Screw 10mm
M3 Nut
1x10 Female Socket Header
1x8 Female Socket Header
1x6 Female Socket Header
PartQuantity
Velostat sheet 1
Copper tape 1
Solid core wire 1
Electrical tape 1
Wood laser cut case 1
Wood laser cut template piece 1
M3 female to female spacer 17mm 4
M3 Screw 10mm 12
M3 Nut 4
1x10 Female Socket Header 1
1x8 Female Socket Header 2
1x6 Female Socket Header 1

Tools you'll need

You will need the following tools

Mechanical Assembly
This video walks through the completel mechanical assembly of the MIDI Piano.

Drawing a guideline 

When you take the wood case out of the box, it will have one spacer screwed in with two M3 screws. This is so the case is not smashed in shipping. Unscrew the top half of this so the case can lay open up. With the wood case laid flat and open, locate the three other outer holes on the lower half of the case similar to the one the spacer is already in. Begin by attaching your remaining spacers into these holes and securing them with one screw on the bottom. Fold the center hinge so the top half of the wood piece rests nicely on the spacers. You do not need to secure the top screw for this part as you'd have to take it out later.

Now press a key down and look at the side. See how the key hits the case only on the bottom edge of the key? That small amount of contact area of the key to the base is where we want our copper tape to be.

Take a pencil and using your other hand hold down all the piano keys at once. If you didn't secure the top of the wood piece, check to make sure the holes on top line up with the spacers. With a sharp pencil draw a line as close as possible to the contact point between the keys and the bottom of the case. If any screws were used on the top remove them once a line is drawn, leaving the spacers in place. We now have our guideline for where our ground plane will be.

Place the standoffs in through the bottom piece of the laser cut piano.
Place the standoffs in through the bottom piece of the laser cut piano.
Screw the standoffs in place.
You will need to ensure the screw holes in the standoffs line up with the holes in the laser cut piano.
Press all of the keys and use a pencil to draw a line through the contact point of the keys.
Line marking contact point of the keys.

Ground Plane with copper tape 

This part requires a sharp pair of scissors or an exacto knife to cut the copper tape.

Measure a piece of copper tape approximately 1.5 times the width of the base of the wood case along the line drawn. It does not have to be exact as it can be cut down later. The goal for this step is to apply the strip of copper tape along the line drawn. The contact point of all of the keys need to be as close to the middle of the copper tape strip as possible. This may involve adjustment to make sure the copper tape is in the correct place.

Before removing the back paper of the copper tape, be aware the copper tape curls once it is removed. You can avoid this by sticking one end of the tape to the wood and pulling away the paper.

Start from the right side of the wooden board and place the tape so it centers on top of the guide line drawn. Once at the end of the board we want to fold the tape up toward the spacers. Fold the tape back at a diagonal ** \ ** so the adhesive side faces you. Then fold up towards the spacers so the adhesive sticks down, making a right angle where we folded it.

Make sure the copper tape's end edge isn't too close to the spacer as we need room to attach a wire to the tape later on.

Place a piece of copper tape along the line.
Place a piece of copper tape along the line.
Fold the tape when you get to the end of the line.
And run the remainder up towards the standoffs.
Secure the tape. Ensure only one continuous piece of tape is used. If the tape tears, remove all of it and start over.

Attaching Velostat 

Grab the Wood laser cut template piece, it's size and engraved lines are going to help you cut the velostat strp for the base. The engraved portion in the middle is where the copper taper will be aligned to. The velostat strip will be the length of the board at the drawn line, and as wide as the template. Feel free to mark the velostat with pencil marks to make a clean cut. Cut two pieces of electrical tape slightly longer than the velostat, with room to fold over the edges of the wood base. Place the velostat evenly over the copper tape. Take on of the pieces of tape and place it over the velostat edge, enough to hold the velostat down but not to cover where the copper tape is underneath. Make sure the velostat is flat against the wood, and place the remainging tape on the other edge. Fold the tape over the edges of the wood to secure it.

Grab the velostat and template piece.
Grab the velostat and template piece.
Cut the velostat the length of the board and width of the template
Lay the velostat evenly across the copper tape
Tape the velostat down with electrical tape
Fold the of the electical tape over to secure it

Key Contacts 

Cut seven copper tape strips slightly longer than the length of the keys, you can be generous with your cuts because the copper tape will wrap around to the other side of the key. Any extra tape can be removed later. Attach the copper tape by starting on the underside of the key right before the key's hinge, and wrap it around the keys edge over the top of the key. Cut the copper tape on the top side of the keys for a clean finish.

The copper tape on the keys are the last piece to create a finished circuit between the ground plane, velostat and keys. Every press while playing the piano will close the circuit, sending information to the arduino.

Cut seven copper tape pieces for the keys
Cut seven copper tape pieces for the keys
Attach the copper tape so it wraps around the key
Trim the copper tape on the top of the keys

Soldering the Copper Tape 

Soldering to copper tape is like soldering to anything else. The only problem is that copper tape is thin. We don't want to keep our hot soldering iron on the copper tape or close to the wood for an extended period of time. If your soldering iron has the option medium heat is sufficient. Always clean and tin your soldering iron.

Open up the case so it lays flat and you have every inside end of the copper tape available to you. For the ground tape across the base, the end closest to the spacer will be the one you apply solder to. Take the soldering iron and solder and hold it over the tape. Lightly apply the iron to the tape and feed the solder into the iron, creating a blob of solder on the tape. You can be generous with the amount of solder on the tape, creating a nice round blob about 1/3" long. The goal is to create enough height for the wire to sink into. Do this to each one of the tapes until all eight ends are set. Make sure to clean your iron between each tape to get off the residue from the copper.

Cut 8 wires approximately the length of the outstretched wood case. These will be longer than you need, but gives you wiggle room later on. Strip both ends of the wire about the width of a finger. Take the soldering iron and place a wire end on the solder blob. The rest of the wire should go towards the end of the tape and the center of the wood case. While resting the wire end on the solder blob, gently apply the soldering iron to the blob. It will heat up the blob and the wire should sink in. Quickly remove the iron and allow the solder to harden before letting go of the wire. Make sure you move quickly so the heated solder doesn't flatten out, leaving nothing to cover the wire. If this happens, leaving the wire unsecured, apply more solder on top of the wire to cover it.

Do this for every copper tape end, and your result will have 8 wires all pointed towards the center of the wood case. These wires may be in the way for the next step, so feel free to bend them slightly to make room for the arduino mounting on the center of the case. You can optionally cover the new connections with electrical tape to create a finished look.

Soldering the copper tape on the inside
Soldering the copper tape on the inside
Gently feed solder into iron on end of the tape
Create a solder blob
All tape ends soldered
Cut and strip the wires
Lay the wire on the solder blob and heat it up
Let the wire set in the melted solder
Finished wiring

Mount Arduino 

Take your Arduino Uno, four M3 screws and the four M3 nuts. Place the Uno so the mounting holes on the Uno match up to the remaining holes on the bottom half of the wood case. The analog and power pins should be closer to the hinge of the case. Take a M3 screw and push it through the hole of both the arduino and case. Screw the nut on the underside until it is secure. Do this to the remaining three screws on the other holes.

Note: Having the screws come up from the bottom of the case makes them flush with the screws attached to the spacers, but it is harder to attach the nuts on the arduino side.

Take the remaining female headers and attach them to the pinouts on the arduino. You won't be able to press them in all the way, and about 1/4" of lead will be exposed. You won't have anymore headers remaining after this step.

Screw in the ArduinoScrew in the Arduino Attach the remaining headers to the ArduinoAttach the remaining headers to the Arduino

Feed Wires 

On the top half of the wood case is a small slit next to the arduino shaped hole. Bend each wire so it can snugly fit through the slit and stick out to the top of the case. It is recommended to do this in a specific order so you know which wire is which later on.

Bend the case closed, keeping the wires sticking out through the slit on the top of the case. The wires should not have any tension with the case open or closed. Secure the top of the case closed with the remaining four M3 Screws. The headers coming up from the Uno should stick out of the center hole.

Wires fed through slit in specific orderWires fed through slit in specific order

Attach the Shield

Take the PCB Shield and attach it to the Uno headers, pressing it in until the shield is stable. You may need to gently bend the long leads of the shield to get them to fit into the headers perfectly.

Wires should be sticking out of the slitWires should be sticking out of the slit Attach the shield to the Uno headersAttach the shield to the Uno headers

Routing the wires correctly 

Even if you ordered the wires before this step, double checking before trimming the wire could save you from having to replace it. Since all of the wires are the same color and could get out of order while doing previous work, this step guarantees you are working with the right wire. We will be using a Multimeter for this step, if you do not have one you'll have to unattach your shield to open the case to check the order of your wires.

Most multimeters will have a continuity test feature that can be selected. The continuity test will make a beeping noise if two connection point are a part of the same connection. In other words, if both ends of a wire are connected to each other the multimeter will beep. Now let's put this idea to work and find which wire is suppose to go into which header pin.

Take one of the multimeter's probes and place it on the copper tape of the 'C' key, now take the other probe and make contact with one of the wires. Does the multimeter beep? If so that wire is connected to the 'C' Copper tape. This wire will go into the '0' pin on the MUX0 header.

Take the wire for C and gently fold it over the pcb shield to get a general feel for where you should cut it. You don't want to pull it too tight for this step or it will have tension that could keep you from opening the case later. With the wire stretched out over the pin it will be placed in, cut it where it's length goes to the far edge of the multiplexer. This can be cut down a bit more depending on how tight you want your wires to be. Restrip the wire at least 1/4" and place it in the header.

Repeat this step with all of the following keys, until each wire is connected correctly. Repeat this step with the ground wire, but connect it the the GND pinout on the upper header. You will have empty pinouts on the header left over.

Here's a quick table of each key and it's wire to the pin on the MUX0 header:

Key Pin
C 0
D 1
E 2
F 3
G 4
A 5
B 6
Tools needed to route the wires
Tools needed to route the wires
Use the continuity function on the multimeter to test the wires
Fold the wire over and measure where it reaches the far side of the multiplexer
Cut the wire
Strip the wire about the width of a finger
Place the wire into the correct pinout
All wires placed

When you're all done screw on the last remaining four M3 screws onto the top holes of the wood case, securing it down. The shield does not need to be screwed down. You've now completed setting up your MIDI Piano!