[sdiy] 566 Functional Replacement

[Richie Burnett]

No wasn't being sarcastic.  I only saw the "8-bit PIC" part, so assumed an 
8-bit DAC output.  Sorry, didn't read that it had to be 8-pin too.

-Richie,

-----Original Message----- 
From: Tom Wiltshire
Sent: Monday, March 19, 2018 9:32 PM
To: rburnett at richieburnett.co.uk Burnett
Cc: synth-diy at synth-diy.org
Subject: Re: [sdiy] 566 Functional Replacement

I was thinking Pulse Density Modulation so that the output is only a single 
pin. Other approaches are possible, but you’re not going to get much of a 
R2R DAC on an 8-pin chip.

Were you being sarcastic/ironic? It’s so hard to tell via email…

T.

> On 19 Mar 2018, at 20:31, Richie Burnett <rburnett at richieburnett.co.uk> 
> wrote:
>
> R2R DAC for the triangle output Tom?
>
> -Richie,
>
> Sent from my Xperia SP on O2
>
> ---- Tom Wiltshire wrote ----
>
>> This *is* definitely a 8-bit PIC design. Here’s a sketch:
>>
>> Run an NCO as fast as you can. Output a triangle wave. You minimise the 
>> problems caused by aliasing, since the harmonics roll off so fast, plus 
>> you can whack the sample rate way up since all you need to do to generate 
>> the waveform is invert the phase accumulator for the second half of the 
>> wave. Wave output goes through a simple RC filter off chip, then back 
>> through an on-chip comparator for your square output with no aliasing 
>> either. Bonus points if you can open up the other comparator input to 
>> allow PWM.
>>
>> Tom
>>
>> ==================
>>      Electric Druid
>> Synth & Stompbox DIY
>> ==================
>>
>>> On 19 Mar 2018, at 16:26, Tim Ressel <timr at circuitabbey.com> wrote:
>>>
>>> When I sed 'VCO' I did not mean a full-featured volt per octave VCO. I 
>>> literally meant an oscillator that has voltage control. Cv in, triangle 
>>> and square out, thats it. thats what the 566 did. that is what I want. 8 
>>> pins, 5 passives, and you're in business. thats what the 566 brought to 
>>> the party.
>>>
>>> -t-i-m-b-o-
>>>
>>> On 3/19/2018 9:21 AM, Mattias Rickardsson wrote:
>>>> Some thoughts about the dream VCO discussions here:
>>>>
>>>> What would be the main reasons for wanting a tiny VCO IC?
>>>> I can find it hypothetically attractive, sure, but given that it will 
>>>> never have many features AND a small size at the same time, I'd almost 
>>>> always need to add stuff outside in the end since you rarely want just 
>>>> the basic functionality. If I'd use a dedicated VCO IC I'd rather have 
>>>> some features that are sometimes not in use than having to add 
>>>> near-basic functionality with external components. The only true reason 
>>>> for a small chip that I can come to think of is cost. I guess it 
>>>> somehow scales with size in IC fabrication?
>>>>
>>>> Making wishlists with VCO features, ending up on the 3340 specification 
>>>> from 38 years back... aren't we missing something? :-)=
>>>> Many modern analog oscillators (both in modulars and in hardwired 
>>>> synths) have other features than the ones we had in the '80s. This 
>>>> should be reflected a bit in the wishlists we make for VCOs today, even 
>>>> if most of these features could be added outside the main chip. 
>>>> Exponential and linear CV should be mandatory, triangle/sawtooth/square 
>>>> outputs as well - and I'm thinking that a triangle core would be the 
>>>> way to go, even if proper sync needs to be dealt with in a less obvious 
>>>> way. That said, we're still stuck in 1980. Sine shaper, thru-zero FM, 
>>>> what more is desired for the synthesists of today? :-)
>>>>
>>>> Btw, Tim P, that negative expo CV allowing a single inverting CV summer 
>>>> is a smart choice. What about the double cap pins in your suggested 
>>>> pinout? Do they give a better solution than the cap-to-ground used in 
>>>> both CEM and SSM ICs?
>>>>
>>>> /mr
>>>>
>>>>
>>>>
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>>>
>>> -- 
>>> --Tim Ressel
>>> Circuit Abbey
>>>
>>> timr at circuitabbey.com
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>>
>>
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