Stylophone

Introduction

This page is a tutorial for making a stylophone using a Makerspace stylophone kit. A stylophone is an analog electronic instrument invented in 1967 by Brian Jarvis. It is similar to an electronic keyboard but a stylus is used to “press” the keys rather than the keys being physically pressed. When a key is “pressed” a circuit is completed that results in a note being played.

Electronic projects can seem intimidating especially if your new to them, but do not worry you can do it! There are details in this tutorial that I have included for people familiar with electronics, but it is doable to make a stylophone without understanding them. The big picture to focus on is that the goal is to put electronic components onto a printed circuit board (PCB) to create the circuitry for the stylophone. The PCB has "through holes" that the components can be put through, and the components are connected by "traces", which are just pieces of copper embedded in the circuit board. Below is an image of the Makerspace stylophone PCB without any components placed on:

-put image of component free PCB here

Components are placed on the PCB by putting them into the holes and soldering them into place. Below is an image of the Makerspace stylophone with components soldered on:

- put image of PCB with components here

Key Parts of the Circuit

The circuit for the Makerspace stylophone is composed of four major portions. A voltage controlled oscillator (VCO), a resistor ladder, buffer, and an audio amplification circuit:

• VCO - this portion of the circuit outputs an oscillating electrical signal whose frequency depends on the voltage at the input. By varying the voltage specific frequencies, and hence notes, can be played.
• Resistor ladder - this portion of the circuit is a series of resistors that sets the voltage that is inputted to the VCO, therefore setting the note played by each key
• Buffer - isolates the VCO circuit from the resistor ladder circuit.
• Audio amplification - this portion of the circuit takes the oscillating output from the VCO and amplifies it so that the signal can be sent to a speaker and converted to sound.

Below is an image of the the circuit board with each part of the circuit outlined:

- Image of circuit board with each portion of the circuit labelled

Materials

The Makerspace stylophone is an electronic circuit primarily composed of three types of analog electrical components: resistors, capacitors, transistors, and op-amps. On the circuit board most components are labelled with a name. Below is a list of components needed to build each portion of the stylophone as well as their names on the circuit board (if applicable).

Circuit Components:

Resistor Ladder:

One resistor per note as well as a grounding resistor RGL and tuning trimpot R_T.

• R0L - 1 x 10kΩ 1% resistor
• R1L - 1 x 6.81kΩ 1% resistor
• R2L - 1 x 6.98kΩ 1% resistor
• R3L - 1 x 7.68kΩ 1% resistor
• R4L - 1 x 7.87kΩ 1% resistor
• R5L - 1 x 8.25kΩ 1% resistor
• R6L - 1 x 8.66kΩ 1% resistor
• R7L - 1 x 8.87kΩ 1% resistor
• R8L - 1 x 9.53kΩ 1% resistor
• R9L - 1 x 10.5kΩ 1% resistor
• R10L - 1 x 11.3kΩ 1% resistor
• R11L - 1 x 12kΩ 1% resistor
• R12L - 1x 12.7kΩ 1% resistor
• RGL - 1 x 100kΩ 1% resistor
• R_T - 1 x 100Ω trimpot

Buffer:

• BUFFER_OPAMP - 1 x MCP 6002-I/P op-amp
• BUFFER_C - 1 x 10 nF (103) capacitor

VCO:

• VCO_R5, R8, and R9 - 3 x 10kΩ resistor
• VCO_R1, R2, R4, and R7 - 4 x 47kΩ resistor
• VCO_R3 and R6 - 2 x 100kΩ resistor
• VCO_OPAMP - 1 x MCP 6002-I/P op-amp
• VCO_C - 1 x 10 nF (103) capacitor
• Q1 - 1 x 2N3904 transistor

Audio Amplification:

• BTE-PAM8403 audio amplifier
• AUDIO_C - 1µF (105) capacitor

Other Components:

• Makerspace stylophone circuit board
• 8Ω speaker
• AA battery holder
• Stylus

Placing Components and Soldering

With circuit board and materials ready it's time to place the components and solder them onto the board.