[time-nuts] 50/60 Hz clocks
lists at rtty.us
Wed Mar 23 23:23:56 UTC 2011
You can do the drop / add pulse thing with a sub 50 cent micro. The only real sorting function is that you rule out the ones that won't take an external 10 MHz clock. If you want pseudo sine wave with PWM that likely will fit. We're only driving a motor here, low distortion is hardly a requirement.
On Mar 23, 2011, at 7:20 PM, Chris Albertson wrote:
> On Wed, Mar 23, 2011 at 3:18 PM, Mark Sims <holrum at hotmail.com> wrote:
>>> it doesn't have to be THAT complex. A 500000 entry LUT is however expensive.
>> Yeah, might even cost as much as a whole US dollar (ragged as they are these days). 512 kbyte EPROMs can be had for under $1... connect the outputs to a resistor ladder (might need an output latch), filter, voila rather nice sine wave.
> I think if you really needed a 500K entry LUT then each entry would
> need to be 3 bytes wide or you loose the point of having a large
> table. So you are up to a 1.5 Mbyte table. That said a sine wave
> can be compressed. First off you only need to store 1/4 of the wave.
> Then because the function is monotonic you only need the deltas from
> the last sample and we assume the first sample is zero. The wide
> table could easy be compressed to 512K
> But even so, one can buy a small micro controller with way more than
> 1.5MB for only a few dollars. Or for that matter AD will give you
> sample DDS chips for free if you ask.
> Chris Albertson
> Redondo Beach, California
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