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Picture of A Fantasy on the Stylophone Theme

I decided to make an electronic musical toy as a Christmas gift for my little son. I browsed the Web looking for inspiration and found the Stylophone, a device on which I based my own design. In fact, I replaced short keys of the Stylophone with long ones, thus creating a kind of writing pad. Indeed, you can write characters and even words on this pad, and every character would have its own ‘sound portrait’. I think it would be useful for children who learn to write, making the learning process amusing.

This article was also published today (21 February 2019) in Nuts and Volts, a magazine for amateurs of practical electronics. http://nutsvolts.texterity.com/nutsvolts/201901/MobilePagedReplica.action?pm=2&folio=32#pg32

Step 1: Circuit

Picture of Circuit

The circuit is basically an astable oscillator built with an

IC 555; you can find a description of how this circuit works, for example, on www.electronics-tutorials.com . The frequency of the oscillations depends on the values of R1, R2 and C1, and is calculated as:

(1) f = 1.44/(R1 +2*R2)*C1

Therefore, if you want to change the frequency, you should change either R or C. When playing a Stylophone you change R2 to change the frequency of the sound. I transformed the formula (1) to separate R2:

(2) R2 = 1/2* {1.44/(f*C1) - R1}

The range of my device includes 12 notes – from C6 (chosen at will) to C5#/D5b; the reason of this is purely geometrical – I used an available wooden box (198 x 98 x 31mm) as the enclosure for the device, and available aluminium stripes 7 mm wide; so, only 12 keys fitted in the width of the box.

C#5/Db5 554.37

D5 587.33

D#5/Eb5 622.25

E5 659.25

F5 698.46

F#5/Gb5 739.99

G5 783.99

G#5/Ab5 830.61

A5 880.00

A#5/Bb5 932.33

B5 987.77

C6 1046.50

A complete table could be found here: http://pages.mtu.edu/~suits/notefreqs.html

Let’s take R1 = 10 kΩ and C1 = 100 nF, then R2 for the
frequency of C6 (1046.50 Hz) calculated with the formula (2) is 1876 ohm (rounded to the whole number). The values for other frequencies can be calculated in the same way; the lower the frequency, the bigger the value of R2. Let’s add a series of resistors (R3, R4, etc.) to R2; then, as you touch the point ‘Key1’ with the stylus, it’s (R2 + R3) that are connected to the circuit; when you touch the point ‘Key2’, you connect (R2 + R3 +R4), and so on. Thus, the value of R3 is calculated as:

(3) R3 = 1/2*{1.44/(f(B5)*C1) - R1} - R2,

where f(B5) - is the frecuency corresponding to the note B5

The other values are calculated in the same way, they are indicated in the bill of materials. If you need to calculate new values, you can use an online calculator, for example, one from this site: www.ohmslawcalculator.com. The values of the resistors not being standard, it’s necessary to combine a required value from standard ones; however, you might replace permanent resistors with trimmers and establish the required values using an ohmmeter.

The circuit is mounted on a perforated plate, connections are made with flexible wires. I suggest to position the components on the plate exactly as they are positioned in the circuit diagram.

schaapkameel4 months ago
very cool!
Alex Kov (author)  schaapkameel4 months ago
Thanks!
jessyratfink6 months ago
This is great! I could see if being lots of fun to trace upper and lower case letters this way :)
Alex Kov (author)  jessyratfink6 months ago
Thanks for your feedback, it made me also think about a possible game 'Guess what character I wrote' - is it an 'i' dotted with a long dot or a 't' crossed with a very short line?
Alex in NZ6 months ago
This is a really neat idea, and a brilliant update for the stylophone. Thank you for sharing this :-)
Alex Kov (author)  Alex in NZ6 months ago
Thanks for your appreciation. Indeed, I wanted to kind of relaunch the stylophone by widening its possibilities, thus making it more interesting for people