Introduction: Turn a Calculator Into a Musical Instrument

Picture of Turn a Calculator Into a Musical Instrument

Hello this is Wozn from the band Rooftop Ridicule and tonight I'm going to show you how to turn a Texas Instruments TI-85 Graphics Calculator into a playable musical instrument.

This is a device never even intended to make sound at all.

This is a hack in the category of Circuit Bending, but unlike most circuit-bent projects I intend this to be actually used musically, not just crazy noises, although I love those.

These same principles can be applied not only to other Texas Instruments Calculators, but anything that makes sound and has a little brain that you can change the speed of. Changing the "clockspeed," as it is called, will often also change the pitch. Sometimes when set extremely high or low cool crashes and weird noises will occur, especially in toy keyboards.

Step 1: Hardware: Headphone Jack

Picture of Hardware: Headphone Jack

For the TI-85 to make sound, assembly language programmers developed techniques involving sending pulses from the linkport. Some programs can even play 4bit samples! The linkport is already a submini headphone jack, so all one would need to get sound out of the thing is an adapter to the standard headphone 1/8" size.

Not good enough. On mine I opened her up and added a headphone jack next to the linkport. I could have replaced the linkport, but I wanted to maintain compatibility with a normal pc-link.

I also added a tiny speaker that connects to the linkport when a switch is flipped, but the speaker is way to quiet without an amplifier so I don't recommend this. Although if you want to do it this is the chip to use: LM386

Step 2: Hardware: Pitch Control

Picture of Hardware: Pitch Control

As I mentioned in the introduction, one can control the pitch of the sound by changing the clockspeed of this thing's little processor. It is a tiny computer after all, and in fact it has a z80 processor just like the classic Tandy TRS-80 computer.

How do we do it? First you have to open it up and find capacitor C9. Take a look at the picture of it's location taken from one of the sites I linked below. What you want to do basically is remove it and in it's place put a capacitor of another value.

less than 22pF makes it faster and sound higher pitch. no capacitor is the fastest.
more than 22pF makes it slower, lower pitch, and potentially really cool sounding.

RadioShack has a "low pF capacitor" assortment pack that is perfect for this.

You can use several and have a switch to switch between them. The best way however is to use a lower value capacitor and a variable resistor in a configuration where you can tune it. After all how good is a musical instrument you cannot tune?

Unfortunately I do not remember the specific value of the variable resistor or capacitor I used. It it a very small trim-pot and a low value, probably 5k. You can use full size capacitors, you do not have to use a surface mount one like you removed. Radioshack has a trimpot assortment pack too.

The best way to find what works for you is to solder two short wires to the pins for C9, then use alligator clip wires or breadboard to test your speed control first. Be sure you have your computer nearby to put the software on there after you hook it up, it won't keep it's programing with the case off because the back panel holds the backup battery.

For extremely detailed speed mod instructions go here or here.

Step 3: Software

Picture of Software

Ok, but this thing isn't supposed to make sound, how do you make it do it?

First of all, to run assembly language stuff on this calculator at all you first need what's called a "shell." This is a program for running other programs. You see, TI only designed this calculator to do calculator stuff, not run other people's homemade software. Long ago some industrious hackers figured out how to write a shell for the little guy and hack a backup file so that the first item on the Custom menu points to their shell. Once in the shell you can run any assembly language program you can find or make. Tetris was probably the most popular and when I was in high school that was the thing to do this for. Now the calculator TI built to replace the TI-85, the TI-86, has the ability to run homemade or third-party assembly language programs built in. This is because they actually care about their customer base. wow!

The original shell was called ZShell, and it started it all. The smallest, simplest and most reliable one, and therefore the best for what we're after, is CShell-NT v3.05 available from, really the best single resource for hacking these little guys.

There are a small handful of sound demonstration programs that were made for the TI-85, all a long time ago. Here are my favorites, they each link to the file archives of

Zshell Keyboard (Sound)
American Techno Percussion

Step 4: Rock

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Here are a couple audio examples of a song with the calculator in it. When you hear the short beeps that's the TI-85 though a delay pedal, right after the pause with just guitar.

Spleen of the Machine live at Gallos Las Vegas

Spleen of the Machine Accoustic

There you go! This isn't the only calculator that Rooftop Ridicule uses as a musical instrument however. In the photo below is the Casio VL-1. It is both a calculator and a little keyboard, a perfect combo of the two things Casio is most legendary for. This particular one has controls I added which change the pitch in exactly the same way as the TI-85 except it already has a pitch control pot on the back. It also has touch contacts and a button I call "crazy loud mode."

As always follow us around at or


fritsie123 (author)2009-11-12

Can you add a soundfile of just the TI? It's kinda hard to hear through the guitar and drums.

wozlaser (author)fritsie1232009-11-12

yes very soon

About This Instructable




Bio: my name is Joe Wozniak and I sing, play guitar, mandolin, keyboard, and various circuit-bent things in the band Rooftop Ridicule. It's very likable ... More »
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