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IC 555 instead of IC 50240


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I'm making a chord generator and the scematics call for one 50240, and those are hard to find. I know the top octave divider 50240 can play all the notes at the same time, so it's the perfect tool... but... I need to put together a modern day version that doesn't depend on an obsolete part so here is my idea...

I use one IC 555 for each note in a chord, so if I make the cords with 3 notes, I need three 555s. If I choose to make the chords with 4 notes, I will need four instead. If I understand it correctly, I devide the notes by adding resistors in a chain. (At least that what it looks like for the FutureKit 13-tone organ.)

Is this possible? What parts do I need? Any suggestions on how to wire it?

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Hi,
An old 50240 made accurate frequencies. A 555 makes frequencies that change. You would need to frequently tune each frequency from each 555 if you want music that is in tune.

What kind of sounds do you want? A 555 and most other simple square-wave oscillators make a buzz sound. An oscillator that makes a sine-wave makes a smooth tone like a flute.
Also consider the envelope of the sounds. Do you want it to be bang it is on and bang it is off like a car's horn?

A 555 makes spikes on its power supply that causes interference with other oscillators using the same power supply. The Cmos version of the 555 has less of this effect.

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Remember the vulcan harp project....? Anyways.... I've noticed a kit for a simple mini organ that uses the 555 chip and thought that I could make a chord generator by using in essence three or more kits (without having to buy several kits, just the components).

The flute or organ sound would be OK, because I don't think I can build something more advanced into the space available.

The sound could be "bang on". That's OK, but a softer start, but up to volume quickly would be nicer.

I've also seen the 556 that looks like a double 555. An alternative?

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Audioguru - I hope you don't mean my idea is a bad one because it's based on a kids toy.

Ldanielrosa - let me know if you find a 50240. I'd really appreciate it!

OK... I've been googling a bit more... the CMOS 7555 seems to be a better choice than the NE555, all I need to do is put in the 7555 instead of the 555 in a circuit.

There are some more electronic kits/toys that uses transistors instead of the 555. Would using transistors be a better choice or not?

There seem to be some type of clock/timer inside the 50240 and something that divides the frequency. Would it be possible to build a 50240 replica?

Can a circuit be built around the 555 so that the sound is more pleasing? There seem to be some synths around that is just a box that changes sounds.

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Years ago I bought an electronic piano for my kids. It is very high quality but was inexpensive and they are probably also available today. It has a pitch control so it can be adjusted to be in tune with other musical instruments. It has frequency dividers so its frequencies are always in tune with themselves. It has many "voices" so it reproduces the sound of many musical instruments. It plays chords. I records what is played. Its battery lasts a long time.

You could use the circuit from one for your project.

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Audioguru -  I've been thinking about that, and even opened up my midi keybord (needs fixing anyway because on of the keys have gone silent). There seemed to be quite a lot of resistors in it, and I need to find a proper manual for the innards in order to fix it. I just assumed that all modern toy "pianos" are so digital that it isn't possible to turn it into a chord generator. If all else fails, I'll try that anyway... but...

Google is my friend. I found this http://web.telia.com/~u16130716/oct54all_asm.htm
Please someone help me understand this!

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I haven't been following this thread, but yes, a microcontroller could be programmed to give you the sounds you need. Each output pin could give you a different voice. You should understand, however, that a 555 and micro will both give you a pulse or square wave without additional hardware to make it into a sine wave. Not sure if that is a problem for you or not. If you need a sine wave, you would be better off building a simple VCO for synthesizer.
Here is a sound chip that is actually PIC based and might be a better choice for you than to learn programming a PIC:
http://www.speechchips.com/shop/item.aspx?itemid=2

A link to the data sheet is also on this page. This company also has other sound chips.
Hope this is helpful to you.

MP

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I've been doing some research into what I want to make, and some hard thinking too...
Whenever I google I get pages upon pages about modular synths, and so I'm thinking that what I need is a modular synth in miniature. The problem is that I don't know enough yet to pick out the pieces I need from these pages, so I need some help with that.
I'm working on an experiment found on one site, to see how it sounds. It's based around a NE555, some reistors, an electrolytic condensator and a couple of cheramic ones. I think it will produce a clean sound wave, but I might be wrong. The NE555 is used as an oscillator, the resistors control the voltage for the tone, and the capacitors work as filters, I guess.

Now for the parts of my micro-tiny modular synth... I need 3 tiny vco:s, one for each tone in a chord. I need a filter and/or envelope (ADSR) that creates a more pleasing sound, and an amp. The ADSRs I have found have knobs for setting the different values, but I need just one preset variation, so I think I can skip some parts, I just don't know what parts. I can't figure out how to combine the tiny VCOs with the rest either, because the modular synths are connected via wires and plugs, and I don't need that. I guess I can simply solder one output to the next input, but I'm not sure.

The chords will be preset as well, and according to my calculations, I need just 15 different tones for what I need. It would be great if I could add a transpose knob to the setup, so assuming I put it together for the C-scale I could turn the knob so I can play the D-scale instead. Maybe just a simple trimpot after the battery/power source will do it?

Anyways... any ideas/suggestions? Do you need more specific info on the chords themselves? I'll be happy to tell you more.

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Hi,
A 555 oscillator makes a buzz-sounding square-wave output. The resistors and capacitors determine its frequency, they are not a filter.

To make a chord with 3 frequencies, you need three 555 oscillator circuits. Then you need a simple circuit to mix them together. A filter circuit and an envelope shaping circuit can be between the mixer and the amplifier.

It will be difficult to change 3 frequencies to change the scale or the type of the chord. Key switches or push-button switches usually have only a single contact. Each key or push-button would need a separate one-in to three-out circuit.

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Rotary switches ore pretty common in model railway setups, so I will use those for the preset chords.

The scales... Consider the C major scale (all white keys on a piano). It has a minor parallel (using the same keys) called A minor. I will have one rotary switch for the C major scale and another for the A minor.
The chords... A chord is made up of (usually) 3 notes or more, and the middle note of the chord in its basic setup determins weither or not it is a major chord or minor chord. If you don't use that note in the chord you get an "empty" chord where the major or minor comes from the melody or the strings on my harp. Each scale have thre basic chords, but several of the notes are repeated in different chords, so I won't need a full set of octaves, just the notes I'll use.
Polyphony... this will be created using three different oscillators, one for each note in the chords. The third note is the same as the first, but an octave higher (double frequency).
Transposing... I think I can change key by adjusting the voltage. The voltage is adjusted using resistors, right?

Well... that's the idea so far. On the front of my harp ther will be a volum knob (volpot), a transpoing knob (like a glide), and two knobs for chords. There is a fifth knob on top of the harp, and I will wire plain octaves to that in the same way as the chords. The chord will sound for as long as the switch is set to that chord.

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Hi,
I am sorry to bring up details:

I think you should quickly connect three or four 555 oscillators to a simple mixer circuit and amplifier to see how awful and out-of-tune they sound.
See if they stay in tune after you adjust each one.
See if each oscillator affects the others.
See if a single glide control can transpose all oscillators the same amount (it won't).

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sounds like you are trying to re-invent basic vcos and voltage controls, but going in the wrong direction.

Reptilian: Just look up PAIA electronics and look for schematics for their old synthesizer modules. They used very few parts and had much more capability than what you can get out of a 555. Primarily, you want to look for the 2720 series modules such as 2720-x where x is a number which denotes the model such as VCO, VCA, ADSR, etc. All are controlled by a simple voltage control input and all are connected to each other permanently or by patch cords. They also had a more advance series which were the 4700 series modules.

If you can't find information on any of this, please let me know. I am sure I can come up with examples with a little digging into my archives.

MP

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MP - is this what you mean? http://www.synthdiy.com/show/showproduct.asp?show=942

I've also been looking closer at the http://www.uni-bonn.de/~uzs159/-site. Both look promising.

I am however a bit at a loss as to put the parts together for what I have in mind. I guess all the knobs in the pictures of modular synths are a bit humbling.

I've bought supplies to make my own PCBs so wiring will be easier. I'm also prepared to get a whole lot of resistors, capacitors and transistors to try out any design needed.

This is a pretty steep learning curve for me. A few weeks ago I had no idea what VCO and so on was. Now I'm beginning to understand it a bit. It's fun but confusing.

MP - if you can help me sort out the parts I need from the parts I don't need, and help me understand how to connect the parts, I'd be very very happy!

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You sure are taking on a lot RF.  I hope you don't get bogged down and frustrated.  That willl be a nice toy when it is finished.

The tuning on the original is by an R-C oscillaotr, but only one so everything is in tune with itself.

You asked about microcontrollers earlier.  Do you have programming experience?  You haven't been here long, and your profile doesn't say much.

I don't know what priorities you ultimately have for bells and whistles, but I recommend a method that allows you to get something together that resembles the project long before it is finished.  I have too many things laying about that I never finished because I improved them before I had anything to show for it.

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Hi Rf,
These are exactly what I meant. You will need a VCO for each note of the chord that will be played at once. a low pass filter, high pass, and band pass will be very helpful for fine tuning the instrument that you want to simulate. Then you will run the filtered VCO(s) through the envelope filter which will change the attack and decay of the note. This is what is known as the envelope of the sound. The envelope determines whether it sounds like a piano, flute, oboe, etc. You can attach any and all of these modules together as needed. The keyboard part is just switches allowing higher or lower voltages, depending upon which key is pressed.
Let me know if you need more information. I can probably come up with some patch diagrams as well. What sounds are you going to have come from this instrument?

MP

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MP and Ldaniel - Thank you both!

Background and wanted result: I have musical training in song, piano, guitar, etc. in part as a music teacher (didn't graduate because of the little *@#!!?s), and a strong base of music theory. I've alsways been good at putting things together and my feminin side is into teeny tiny details. When I set a goal I try my best to get to the finish-line with a result that would make an expert proud.
I also work with computers, but my programming is mostly PHP and HTML, not C++ or similar. That doesn't mean I'm not ready to learn if need be. To me, this project is as much a learning project as a proper end-result project, if you know what I mean. I'm academic in nature, but have found it easier to learn stuff when I have to jump in at the deep end.
The instrument I'm building has already strayed from the original blue print, but since the blue print is a construction in itself from a non-working stage-prop, why not? As a musichian I apply the same questions as I did when I designed my model railway station; ease of use, versatility, looks.
The sound I'm after is a warm organ/scifi-sound that can hold long base-notes. I like the way the Hammond-organ sounds, so something along those lines would be fine.
If the IC 50240 were still in production, I would have started with that, but it isn't so I'm looking elsewhere, and Google have been my friend on this journey, as have you.

I found something interesting today after following a link on the second site in my previous post. http://home1.gte.net/res0658s/fatman/4046pll.html I'm not goinf to build an entire Fatman, but maybe this frequency multiplier module can be used anyway? If I understand it correctly, this unit will give me the 5th + octave chords I want, regardless of the starting note? If so, I can turn the tuning knob to any starting note and have the chord played??? It would of course be eaier with preset notes, but 3 rotary switches could give me 12 preset chords or something, and then I wouldn't need a separate tuning knob.

I'll start googling frequency multiplier modules now

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Yes, fatman would give you some flexibility. Also, you mentioned programming. I was wondering if you knew that microcontrollers can be programmed with basic. The PIC can use PicBasic and AVR microcontrollers have Bascom AVR. Even if you do not use it for the heart of your project, it makes for a nice LCD interface, etc.
What are you using for a keyboard? I did not notice if you mentioned this.

MP

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The "keyboard" is made from rotary switches.

On the harp there is 4 knobs on the front, and a 5th knob on the top side. If I use one knob (the 5th) for volume control, I have 4 knobs for my keyboard. My latest idea on how to use those knobs is based on a couple of circuits I found on a synth-site.

If I understand it correctly a frequenzy multiplier works as a harmony generator - input one frequenzy and get 3 (1+5+8). There are 12 half-notes in a cromatic octave. If I divide the 12 half-notes between 3 knobs with rotary switches, I have a spare knob. That knob (rotary switch) will control which one of the harmonic knobs are used (1, 2, 3 or OFF). That way I can set up three "chords" and just turn the selector-knob to the chord I want to play. While that chord is playing, I can select another chord on one of the other knobs if need be. That way I can play continous sounding chords with one hand, and play the strings on the harp with the other. When I don't change chords, I can get half-notes by turning the bottom string-knob (not electronic) if I need to.

I know there are some electric guitar pedals that produces harmony based on the note that is played, so it's not unheard off. I also found a circuit for a keypad harmony synth module that seems promising. I'll do some more reading and then post some links.

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Hi RF,
A major chord is C,E, G and C for example. A minor chord is C, E flat, G and C. Then there are other kinds of chords. C, F, A and C sounds nice but I can't remember what the chord is called.

The phase-locked-loop circuit you found can "follow" the root key "C" in this example and will make both Cs, the E and the G to play a major chord. You would need another PLL circuit to make an E flat to play a minor chord. You would need two more PLL circuits to play C, F, A and C.

You could add ocillators to make vibrato and tremolo if you want.

Instead of a PLL are you thinking of making 12 oscillators then combining them to make your own chords? A 50240 IC did it with digital dividers so the frequencies were always in tune with each other, but it is very complicated to make one.

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Audioguru - imagine you're playing the piano and singing at the same time. Your voice is "playing" the melody. Your left hand is playing the base on the piano, and your right hand is filling in the chords. Your left hand can play one note, or maybe the octave as well, and your right hand playes the 3rd, 5th, and maybe 7th note in a rythmic fasion or arpeggio style. To fatten it a bit you add the 5th to your left hand as well, so in your left hand you play 1st, 5th and 8th note (in C that would be C-G-C).

On the harp, the electronics will be the "left hand", and the strings the "right hand".

In the diagram on http://home1.gte.net/res0658s/fatman/4046pll.html there is referens to 3F in the "Harmonic generator mixer"-box. That is what I want to use. If the input from the VCO is C I get G and C, and if the input is F I get C and F, and if the input is D I get A and D.

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Hi RF,
I realise now the PLL circuit produces a chord with only C, G and C without the E. If you want a complete major or minor chord or any other kind of chord then more PLL circuits are needed.

Have you considered allowing the PLL to listen to the harp then track its frequency?
Do you sing? The PLL can also track the frequency of your voice.

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