[sdiy] Tap Tempo LFO

[Antti Huovilainen]

On Wed, 9 Dec 2009, Tom Wiltshire wrote:

> Maybe I'm misunderstanding you, Antti, but can you explain further, 
> because I can't see how you can make this work with just a uP. With a 
> PLL too, fine.

Of course you do need external circuitry, but you need that in any case 
with BBD, so I don't see that as a problem.

> For example, the PIC 16Fs that I've been using have a max clock rate of 
> 20MHz, and the instruction cycle is 1/4 of that, only 5MHz. This means 
> that if you use the chip to generate a 200KHz BBD clock, you've only got 
> 100 clock cycles per BBD clock, and only 25 instruction cycles. That's

1. You attach a PLL multiplier to the PWM output of the MCU and run the 
PWM at say 1/64 the rate.

or

2. You add a cheap 10 or 12 bit DAC that controls separate high frequency 
VCO with MCU input capture pin used to provide feedback about actual VCO 
frequency.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova