555 based keyboard

[Fluburtur]

I was talking about it a bit on the discord server but Caustic told me to create a thread so here we go.

I have been interested in modulars since discovering LMNC but I dont have the budget to start a modular rig currently so I thought I would do a simpler project, everyone likes the NE555 and I have a 3d printer so I figured I would give a keyboard a try.

I started by ordering some parts and since that would take about 2 weeks to arrive I started designing the actual printed parts for the keyboard, I had pink loaded in the printer because I made some stuff for pink october here so I used that and that earned the keyboard the nickname “Pink Panther”

The keys are printed as one, it relies on a flexible plastic hinge for the movement and it has holes to center the “black” keys over it.
I also designed the keys to be on the wide side so it could be easily playable while wearing a fursuit, this is also sort of a prototype for a future project.

The actual electronics of the keyboard is just a line of switches and 2.2k resistors arranged like a big voltage divider.

I picked 2.2k because I had some of those and it would work ok with the capacitors I have to tune it.
The design is quite simple, just the good old astable 555 stuff where the keyboard is R2 and I will use a trimmer pot as R1 to tune it, I might have to use another trimmer to make both ends in tune tho.

Today I received the electronics I ordered so I started breadboarding, after a long time of chasing very simple mistake I got it buzzing.
I tried using 2 NE555 in parallel to make it sound fatter, they share the same “tuner section” as I like to call it and they go to the speaker through capacitors for decoupling but it gets kinda weird then.

555 keyboard

As you can see in the graph, the waveform is pretty weird.

Single 555 waveform for comparison

I dont know if it is an issue or how to fix it, Caustic suggested a buffered mixer so I think I will do that and I will probably give oscillator its own filter before going into the mixer (it does sound cooler than a single 555 tho)

Anyways that is all I have for now, im sure I will receive plenty of good advice here so im not worrying too much.
If it turns out well I will probably publish the 3d files and schematics.

[Caustic]

Nice, thanks for posting here. This is a cool project!

[Sonosus]

I don’t want to derail this thread this early, but was it by any chance inspired by the Oskitone?

POLY555 DIY Synthesizer Electronics Kit

This is a great idea. Possible expansions could include arcade buttons, stylophone style copper pads(free from AllPCB ), giant floor stomp pads…

Thinking about projects often is more fun than building them

Have fun with it!

[saint_et_moudulard]

haha it reminds me of my first experiments with the “bad” 555

It was my first oscillator.
I can give you my notes if you want.
(if I re-find them in my messy ^^)

• some usefull links:

Simple 555 Based Drone Synth - Sam Vs. Sound

https://www.musicworks.ca/diy/build-your-own-tone-generator

[Fluburtur]

No, I havent done that much research so most of this is what I came up with (but it was probably done before)

I will design it so each board holds one function, so it can be its own mini modular system in a way but mostly so it is easier to work on stuff but I might add stuff later, I was thinking about a small sequencer.

[Jos]

@Fluburtur

I tried using 2 NE555 in parallel to make it sound fatter

If they produce the same square wave, that would not make the sound any fatter. But they probably will not produce exactly the same square wave due to material tolerances in the chip. What might help is if they do not have the same tuner section (which is typically done when one uses 2 oscillators for a basic sound in a modular system) but each have their own with slightly different values. That may lead to detuning which may make the signal sound fatter.

Have you tried a resistor (try 100 Ohm … 1 kOhm) from each 555 to the loudspeaker in stead of decoupling capacitors?

[Dud]

Welcome to the forum @Fluburtur

@saint_et_moudulard me too it reminds me of good memories, long life at 555

[saint_et_moudulard]

@Dud I had for project to build a 55Synth… (sorry the joke doesn’t work in english …) ^^

This timer allows a lot of various designs possibilities !!

clearly, this chip is an usefull real crap!

[Caustic]

the 555 can even be used for envelopes its crazy.

[Fluburtur]

I did some more breadboarding and as it turns out, the weird waveform is probably caused by the capacitors and the fairly large speaker.

I also made a transistor buffer based on the BC547 because I have a bag full of them, I also tried to add a filter but again I think the speaker loaded it down so it didnt go well so the next step is probably to build an output stage to deal with that.

I will probably start assembling the circuits on perfboard soon as well.