Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[jamiewoody]

i am ready to try this now! (well, i will be when i order components...).

what i need to do is carefully plan this out before i start building it. thanks to everyone here for advice on components, etc.

so, far, my plan is to make a 555 tone generator. instead of using a potentiometer for the pitch control, do a parallel circuit of push putton switches where the pot would normally be. i will use trimmers to tune the "keys".

i still like the idea of an actual keyset. i have one or 2 keyboards laying around which i am sure i will never use again, so i may harvest 12 keys and see what i can come up with. maybe i can place the push buttons under the back side of the keys?

[Dylan]

I found this the other day. You may be interested in Page 9 http://experimentalistsanonymous.com/diy/Schematics/Oscillators%20LFOs%20and%20Signal%20Generators/555%20BASIC%20astable%20theory.pdf

[jamiewoody]

thanks dylan, i'll check that out...i am actually close to this now! check out my BASS PEDALS thread on the synths forum! ;-)

[computer at sea]

I bet you could also do it with a couple of 40106's and trimmers.  Each 40106 could give you 6 notes which could be tuned (albeit somewhat roughly) with the trimmers.  While you wouldn't have super tight pitch control, you would have tons of polyphony.

[jamiewoody]

i'm thinking about trying some different circuits. i breadboarded it with a 555 and it seemed to work. i may build at least 2 different keyboards into one box, well, one keyboard controlling 2 different VCOs...

right now, i need to order components, which i cannot do...but as soon as i can, i will be happy.

[moordenaar]

It is very simple to make a VCO with a 555. Just inject a voltage into pin 5. So you can also set the pitch with voltage instead. Or you can ad an LFO.

[jamiewoody]

this is very similar to the VCOs i have been building. even before i ever looked at a drawing of one, and just soldered the components together...(this was my method before i got my breadboard. solder and pray it works...80% of the time, it did!).

the only difference was r1, maybe that 220k resistor would make a huge difference.

i would like to get lower pitch, if my memory serves me correctly, do i go with bigger caps?

[moordenaar]

the only difference was r1, maybe that 220k resistor would make a huge difference.

i would like to get lower pitch, if my memory serves me correctly, do i go with bigger caps?

220 K   No mate that's just 220 ohm. Also it should't make any difference it's just there to control the "volume," so you could replace with a pot.

Yes, bigger caps = Lower Hz

[druzz]

i was also thinking about making some sort of keyboard for my squarewave things . what i thnik i'll do is install a couple of push buttons (5 or 7)  that closes the circuit and re-routes it  trough a different pot for each switch .

so you can tune each note like you want easily  and play little melodies ''morse style'' in the weird unconventional scale of your choice  . 


have fun with youre project

[Gordonjcp]

"Real" analogue monosynths often use a chain of precision resistors with the keys wired across them so that you end up shorting a section of the chain when you press a key.  This way, you don't get out-of-tune noises when you press two keys at once and the highest key always "wins".

[untune]

"Real" analogue monosynths often use a chain of precision resistors with the keys wired across them so that you end up shorting a section of the chain when you press a key.  This way, you don't get out-of-tune noises when you press two keys at once and the highest key always "wins".

That's what I've been curious about lately.  So if you hold a high key, say F3, and then press C3, you wouldn't hear a change becuse it's lower... but if you pressed C4 while holding it the note would change?

[Gordonjcp]

Correct.  Have a look at the scans of the article on the Transcendent 2000 monosynth available on the 'net, and look at how the keyboard circuit works.

These days I'd avoid all the tedious mucking about with precision resistors and the like, and implement a matrix scanner and DAC to generate a true volt-per-octave controller keyboard.  I might do that with my T2000 so I can use it with MIDI...

[untune]

I'll have a look for that now

That's exactly what i've been studying lately but something didn't make sense to me.  If you implement a matrix (using diodes to stop backward flow) I can't seen any way that the circuit can tell which key you've pressed?

http://www.headfuzz.co.uk/midihack1?q=midihack2

Example there.  I see how everything connects up, and with the resistors the resitors would give each key a unique voltage I assume, but how does it work in the case of a microcontroller?  I've been looking everywhere for the past 2 days and nowhere seems to have a definite explanation of it, they all assume that you know that bit already

[Gordonjcp]

It does explain it...

What you do is, you switch on each of the five rows in turn, and read the eight columns.  From that you can tell which keys are pressed.  You scan through the five rows very quickly and at a steady rate, so that there isn't a noticeable delay between pressing a key and the note sounding.

So, in your microcontroller you have a timer set to fire an interrupt every 1/1000th of a second (for example).  Every time the interrupt fires, you read each key as quickly as possible (actually twice, because you want to debounce the keypresses, but ignore that for now).  Put every key that's pressed on a list, and remove any keys that are no longer pressed from the list.  Depending on which key you want to have priority, decide which note you're actually going to play.  For a "classic" monosynth keyboard, take the highest key that's pressed.  For a "classic" polysynth keyboard, take the most recent N notes where N is however many voices your synth has.

[untune]

Of course, makes sense now!  I'd been stuck thinking about resistor ladders rather than reading it logically 

Classic case of wood for trees there.  Cheers for clarifying that