[sdiy] M110 with more outputs

[Neil Johnson]

Hi Andre,

> Not at all, just a random thought. Neil's M110 clone :
>
>    http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=4&subsubmenu=1
>
> What the imitation sawtooth sounds and looks like :
>
>    http://www.teaser.fr/~amajorel/mono/sawtooth/
>
> (Waveform badly distorted by the AC coupling so some imagination
> is required to see the 1 x f sawtooth. It's the 16 x f serrations
> that cause the chipmunk chainsaw effect.)

The M110 takes in a 2.0024MHz clock and uses that to generate the four 
octave outputs.  The same for my M110 replacement.  To generate higher 
tones would need a higher input clock, such as 4 or 8MHz, and then 
further division to get the correct pitch.  This would be easy in my 
M110-clone as I use a 4024 divider on the compare output of the 
ATmega8's counter, and there are a further three outputs which could be 
pressed into service.  However, I don't think the counter would like 
8MHz (the same speed as the micro - no time to synchronise the input).

The proper way to do it would be to do the division in an FPGA (e.g., 
Xilinx Spartan), using an on-board DLL clock multiplier to scale up the 
2.xxMHz clock by a factor of 8, and then do the frequency division. 
You'd also need to provide additional resistors to support the 
higher-frequency square waves, but I guess that's not insurmountable.

While I do plan on using a CPLD to implement some of the interfacing 
logic, an FPGA was not on my plans.

Cheers,
Neil
-- 
www.njohnson.co.uk