this project has multiple pages/parts.
- ‘555’ Noise’ – 6.0.1
- ‘kNoise’ – 6.0.4
Previous builds 0.2 and 0.3 were failures. The project has evolved a lot in the last two builds.
Opening the keyboard revealed a very simple system. There’s a mainboard consisting of lots of momentary switches and an IC. Ribbon wire’d to that board is a long board of 37 momentary contact switches that are the keys for the keyboard. Along with that there is a very speaker, flimsy power switch, and a 2 AA battery compartment.
My plans are to omit the mainboard, and make my own from my crazy 555 noise making circuit. The keyboard will be held like a guitar, using my right hand to control the two 555 knobs. The left hand will press keys on the board to transpose the pitch. The output jack will be the same as a guitar, so that it can easily be amplified by any guitar/keyboard amp without adaptation.
Original Circuitry / Keyboard
So far I have spent a few hours poking around to see how much of the original circuity I could actually use. For now I’ve decided to completely remove the mainboard, and replace it with my own. Therefore none of the original sounds from the keyboard will be tapped into or used. It’s going to be a complete noise machine.
On the keyboard PCB, there are 37 keys and 37 momentary contact switches. I did some poking around on the board to attempt to de-crypt how 37 keys could translate into 16 pins connecting the mainboard. The actual way it’s done is over my head at this point in my career, and I’m not ready to spent a whole lot of time mapping out the entire keyboard for use. For this project, I’ve ruled out most of the keys, and picked 6 that It was obvious where the common point was, and each unique track for each switch. So I literally have six momentary switches that are independent from each other.
Transpose Switching System
‘kNoise’ will have a constant whirring sound of the square waves generated by the 555 chip. The sound will be mainly controlled by R1 and R2 and thumb/index finger. To make this whirring sound more fun, each of the six keys controlled with my left hand will transpose the tone up (higher pitch) when pressed. Each key will add a different resistance value to the existing value set by R1 and R2. The pitch will transpose higher because each key will add a resistor in parallel with the potentiometers. Resistors in parallel reduce the resistance value overall, and lets the electrons flow faster resulting in higher pitch. I’m going to call this “trans-up” mode.
This is were I failedwith v0.2 before (undocumented). Without thinking the switching system through enough, I ended up with a constant whirring noise, and the keys didn’t do anything. I misunderstood how to actually get the key-sistors parallel with the potentiometers.
I had accidentally wiried the key-sistors in parallel with the switch, which did absolutely nothing. This is pretty much just part of my learning process.
The most difficult part so far has been trying to figure out how to use this switching system to switch the resistor network from parallel to series. Series is what will make the keys transpose the pitch down. Resistors in series add to the overall resistance value, therefore reducing the flow of electrons. After a lot of doodling on my paper pads trying to figure out the right way for this to work, I finally got it. Although the only way for it to work is to use two separate switches. The DPST switch (S2) will isolate or connect the key-sistor network to the main circuit in either series or parallel. The SPDT switch (S1) will switch the entire flow from series to parallel. The one problem is that while in Trans-Up mode, the constant whirring will be on, where when in Trans-Down mode, the whirring will only be on when a key is pressed. This is were I made the mistake the first time through – not thinking that it’s impossible to have a constant whirring sound in series since that’s just how series is!
I can live with that. If I need a constant whirring sound, I can hold one of the keys with a finger, while using other keys with other fingers. Besides, it gives the whole project more variety, and difficulty of operation which is kinda what I like.
edit: pin 1 of the 555 chip is supposed to be connected to GND.
This is the final schematic drawing for 6.0.4. In the upper-mid section, you can see the double switch system that puts the key-sistor network in parallel or series.
To make the project simpler and more obvious, I literally made a ground rail. The piece of copper running across the bottom of the board is the common point for everything ground.
Video soon, but not until it’s finished!