Circuit bending the Casio PT-100


I’ve had this keyboard lying around for years (I don’t remember where or when I got it), and after my first bend I wanted to dive a little deeper.

After experimenting I read the writeup at tablehooters and found the chord modes, rhythm select, and sustain mode. I find the prospect of adding functionality that exists in the hardware but simply wasn’t built into the keyboard really exciting. I couldn’t really add more keys and the extra tone selection seemed convoluted. I also read the noystoise article which hinted at a tone select function but couldn’t find it for the life of me. I did discover a fill button which I added on the far left.

sketchup model

This is the final computer model I’d made after many iterations, including one with a banked panel and many more switches and knobs. There’s a deceivingly trim-pot-type element close to the main IC which turned out to be a tank circuit so the pitch knob was out. I was also hoping to replace the six position volume slider with a knob but upon testing it picked up some conservative talk radio. After eliminating some similar bends and discovering the switched potentiometer trick–see below–I narrowed it down to 12 knobs on the upper panel.

In progess:

When I started this project I had very few tools and parts. So while I was waiting for the mail I was estimating the resistance range needed in a bend by the amount my 50k pot was turned. This article led me to believe I could simply limit the range of a pot by adding the appropriate resistors in parallel. That’s true, but what’s left out there is that doing so changes the relationship between knob turn and resistance to a more logarithmic one (see here). So using resistors to change a 50k pot to a 20k pot actually doesn’t add that much control to the sound (depending) and could even make it worse.

Dremeled potMany of the bends I found required switches but after learning you could hack a potentiometer to also act as a switch (see here and the picture) I thought it would be fun and a little nicer looking.

The hardest thing to solder by far was the reverb switch (called “sustain” in the tablehooters article). This involved soldering directly to an unconnected lead on the main IC, pin 90. I could always de-solder it if I messed up so the bigger challenge to me was getting that much heat near the main IC without Tape solderfucking up the chip. Maybe it was unwarranted. I ended up using tape and then super gluing the insulated portion of wire directly to the PCB so it wouldn’t yank loose…

Toward the end of assembly I noticed a few of the pots didn’t have great connections and a couple pots didn’t quite do what they had when tested. I re-soldered and fiddled hoping for the best, but really I felt like that was part of the whole putting-a-shit-ton-of-wires-and-knobs-in-old-electronics deal. Even when it’s finally assembled the process of discovery continues.

Here it is before I squeezed on the back cover:

Overall I’m very happy with this project. I made a lot of tiny compromises, learned a lot, it’s fun to play, and I didn’t totally break anything! I consider that a success.

I do have the specific bends documented and I’ll share them upon request.

          October 21st, 2017

I opened up a gifted keyboard and found an alligator clip and a potentiometer still in the case. So I started poking around and had a lot of fun! This is my first bent keyboard. I really enjoyed making this and I’m currently working on another more ambitious project.

          September 29th, 2017

Hey I made a tape! Let me know if you want one!

          January 6th, 2017

Big drugs little drugs. What begins with drugs?

          June 25th, 2015

I’ve been the organizing force behind a choose your own adventure story with each branch or choice written by a different person. If you’re interested in contributing send me an email. It’ll be a zine and online when it’s done!

          June 19th, 2015

Dichotomous thinking

I was reading a letter in the MOFGA newsletter the other day that sounded to me like some ignorant old man complaining about organic hydroponics: “There isn’t any soil in hydroponic production.” Yes, that’s the idea. And, “Big money is presently invested in ‘vegetable factories’ and ‘vertical farms’ where production is hermetically sealed in huge warehouses filled with LED lights and nutrient pumps.” It’s implied that all these things are wrong, but it’s never mentioned why they’re wrong. And then I see the letter was written by none other than Eliot Coleman who literally wrote the book on small scale organic ag.


          June 13th, 2015

Notes From the Undergrads (story)

“Holy shit, guess who fucking messaged me today”
“No idea”
“Elaine. fucking. Bunter”
“That brainy bitch from psych?”
“With the gloves”
“She’d wear green gloves every day”
“Even in the summer”
“And put her hair in three pony tails”
“I know!”
“Winter gloves in the summer”
“Anyway, get this”
“She’s getting married”
“FUCK! To who? Don’t fucking tell me it’s Jordan Stein”


          June 1st, 2015

Sean’s Gloves (story)

Where the hell did his gloves go? There was an anathema of things going wrong and things going right. Earlier that day he’d been pulled over for speeding–the third time this week–on account of a wily, suspiciously hard of hearing mechanic who, upon handing our hero a large list of tasks performed or needed to be performed on his truck (brake fluid streamlining? Initial response system upgrade? Flester bolts tightened?) with an exorbitant number at the bottom, seemed a bit too confident exclaiming “She’ll really run now!” and now his speedometer was entirely unpredictable and incorrect, Sean guessing there was maybe some kind of exponential relationship between the wheels and needle with no real way to tell.


          June 1st, 2015

Lego computer

I bought legos and computer parts and put them together with hot glue! It runs on 60W of power.

I started with the love for legos, small computers, and design. I used LEOcad to make the intial design and bought all the bricks through, which is a network of lego-selling hobbyists. I kept to my design strictly, but bought used parts from my local FreeGeek when I could. It cost a little more than 300 dollars.


          June 1st, 2015


A 45 minute documentary goof-fest. Finished in 2012.

          June 1st, 2015