[sdiy] Re: Re: [OT] super cheap synthesisers

trevor at resonance.fsnet.co.uk trevor at resonance.fsnet.co.uk
Mon Jun 10 12:09:32 CEST 2002

Hi Theo,

Have you considered the 16F628? If not then it might be worth looking at the specs. The 16F628 is actually rather cheap (making one uC per card quite feasible), is an 18 pin package, has three hardware timers and a USART, etc. It is recommended for new designs and is actually much cheaper than the old 16F84, which is much lower spec. It probably hasn't got all the timers you call for in hardware, but using what it has to implement some software timers would be easy. 

True, there are (often better) alternatives to PICs - I'd probably consider the SX or Xilinx route as opposed to having one uC per card. 



> From: "Theo" <t.hogers at home.nl>
> Date: Mon 10/Jun/2002 09:27 CEST
> To: "Dominic Tarr" <dmt10 at waikato.ac.nz>,  <synth-diy at dropmix.xs4all.nl>
> Subject: Re: [sdiy] super cheap synthisizers
> I've been thinking the same thing for a while now.
> My idea was to have identical "one uC" mono synths,
> programmed to be the 1st, 2nd and so on, voice of a poly synth.
> No global note assignment, but each synth running the same assignment
> algorithm and then responding to the correct note.
> Big problem I ran into is to find a _cheap_ uC with enough timers.
> For 2 "juno style" DCOs you already need two 16 bit timers.
> With "juno stile" DCO I mean:
> Put out the note number to a 4 to 6 bit R2R DAC loading a capacitor
> and use the times to reset.
> The error will be in the amplitude, frequency is rock solid.
> Then you need some more 8 bit timers to generate PWM signals for the cutoff,
> resonance and VCA.
> Problem is that cheap uC generally don't come with 3 or more hardware
> timers and a hardware async serial  interface for the midi..
> The PWM signals for VCF and VCA should preferably run above 40khz and
> on top of that you want enough uC speed left for decent LFO and ENV.
> So away goes the software timer solution, although software timers are
> probably the only way out.
> One option might be to share one timer for VCF and VCA.
> IMHO AVR are a assembly programmers dream, but none of the AVR fit the
> specs.
> Duno, maybe there is a PIC that fits the bill.
> But PIC ain't my first choice, bit slow, ugly structure etc.
> Then again there _are_ pp who actually seem to like the PICs,
> then again again, some pp are into kinky stuff...
> SX maybe a better alternative, fast and have "soft" hardware periphery that
> you may configure the way you  need.
> However they look a bit like the PIC on the programming side :(
> And with the "soft" periphery eating some of your cycles it can become
> troublesome to keep track of your cycle count for time critical work.
> Still SX is probably the best candidate.
> There are new fast 8052 look-a-likes from Dallas and Texas.
> Some of these are both fast and offer two 16 bit and one 8 bit timer,
> but don't think they fit the "cheap" part of the description.
> My 2 cnts,
> Theo
> From: Dominic Tarr <dmt10 at waikato.ac.nz>
> >
> > I'm contemplating building a monophonic synth from a PIC chip (as the
> oscilator) and a vca and vcf and decay eg.
> >
> > either controling the vcf through a heavily low pass a pulse width
> modulated signal to produce a rough control voltage, or a frequency to
> voltage converter.
> >
> > I havn't actually done much electronics, so what are your thoughts on the
> feasibility of all this?
> >
> > cheers - Dom
> >

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