Inspired by the DIY pressure plate design from both Rich Osgood and Make Magazine, and the Floor Piano Performance, my teammates and I made our own giant wireless floor piano at HackDuke. There are four main components in our wireless floor piano system: the keyboard itself, the main control unit (the Sparkfun box shown in the picture above), the handheld remote, and the receiver connected to the laptop. Below is a communication diagram of the entire system.
The Pressure Plate Keyboard
The basic idea is that each key is a pressure plate made of cardboard, aluminium foil, and foam, and when someone steps on it the two sheets of aluminium foil make contact and close the circuit. We first tried the design from Make Magazine, in which a layer of cardboard is used to separate the two sheets of aluminium foil. It worked well at first, but after a couple stomps the cardboard on the top became bent so the aluminium foil were no longer naturally separated. Another problem is that the cardboard on the top couldn’t return to it’s original position and open the circuit in time ,which means that you’ll have to jump very high in order to play the same note again. So here are the two things I realised after making this first pressure plate: first, the aluminium foil has to be glued to the cardboard surface so that there won’t be an area where it’s slightly bent up and could easily make contact with the other aluminium foil; second, we need to use a different material to separate the two cardboard in order for the top layer to return to it’s original position as fast as possible and also make the pressure plate more durable against heavy stomps.
This is when we realised that foam would be the most suited material for the purpose. As shown in the picture above we made another prototype with four pieces of foam glued to the corners of the aluminium foil on the bottom layer, and it works like a charm!
After we’ve finalised our design for the pressure plate, we immediately started our manufacturing process. Each of my teammates is responsible for one step in the manufacturing process: cutting the aluminium foil to the right size, gluing the foil to the cardboard, and finally putting duct tape around the edge of the cardboard for the purpose of insulation. Then we continued to glue the foams to the cardboard and tape down a piece of wire on each aluminium foil. After each key is fully assembled, we put a piece of LED strip on the top of each key. The reason why we decided to have LED strip on each key is not only that it looks really cool when you’re playing the keyboard, but also that we can have the keyboard teach people how to play it by lighting up the correct LED strip.
Now it comes to the point where we have to make connections between all the keys. In the very first panorama you have seen that our keyboard is split into two parts, the left part with 12 keys and the right part with 13 keys. We want our keyboard to be easy to carry around, so we decided to make it foldable by leaving a space between the E and F, and also some space between the black keys and the white keys.
The Main Control Unit
Each key have four wires coming out of it: +12V and GND for the LED strip, and the input wire and GND for the two aluminium foil. The +12V of all the LED strips are connected together, and the GND of each LED strip is connected to the collector of a TIP120/31/41 transistor. The GND from all the bottom aluminium foil are connected together, and each top aluminium foil is connected to a input pin on the Arduino Mega. Therefore the left keyboard requires a total of 12+1+12+1 = 26 connections, and the right keyboard requires a total of 13+1+13+1 = 28 connections. Since I don’t have any ribbon cable that have that many pins, I decided to make my own cable by taping together 26 and 28 pieces of jumper wires. Here’s a picture of the inside of the main control unit.
All the white wires connected to the male headers are inputs from the top aluminium foil. All the black wires connect to the base of the transistors, and all the colour wires go to the collector of the transistors. All the input pins on the MEGA are pulled high, and once there is a input connected to GND (pressure plate is being pressed), the output to the corresponding transistor would be pulled high and the LED on that key would light up.
The XBee sends note values to the receiver XBee connected to my laptop. A value of 1-25 indicates a note is pressed, and 26-50 indicates that the note is released.
On the back of the box there are two switches, each controlling a battery source, two power jacks – one 12V going to the LED and the other 9V to the Arduino, and the USB port.
The Remote Control
The remote control is built around an ATtiny85 running at 8MHz. The major functionalities of the remote control are: changing octaves, switching between 16 MIDI channels that are each set to a different instrument, and enter the tutorial mode in which the LED on the keyboard would light up to tell you how to play a song. Using SoftwareSerial, the ATtiny85 is able to talk to the XBee at the 31250 Baud rate, and this XBee then sends the value to the receiver. A value of 51 and 52 moves the octave down and up respectively, and a value between 60 and 75 indicates switching between channel 0 through 15.
The tutorial mode is one of the best features of our floor piano system. Currently, these tutorials are just stored in the form of an int array on the Arduino Mega. To start the tutorial, one presses the white button on the remote control, and a special value would be sent to the receiver connected to the laptop. The receiver then acts as a relay and send this message to the main control unit. After the message is received by the Arduino Mega, the tutorial starts and the first key in the tutorial would light up. In the future we plan to add the functionality to allow people to record tutorials by playing the keyboard instead of storing the note values in the program in advance.
The receiver that’s connected to the laptop is the simplest of all four components. It’s just an Arduino + XBee shield +Xbee. The ATmega8u2 chip on the Arduino is flashed with the MOCO firmware, which converts the serial MIDI data to standard MIDI messages, making the Arduino a real MIDI instrument.
Portability of The System
The entire system is very potable; you can easily carry it around, put it down and start playing anywhere you want. As mentioned above, both of the two parts of the keyboard are foldable in the middle, and optionally between the black and white keys. The jumper wire cable, the remote control, and the receiver can all be stored in the sparkfun box.
All Arduino Code can be found here: https://github.com/jl452/super-saiyan/tree/master/Wireless%20MIDI%20Floor%20Piano