Re: PIC + DDS = Frequency Synthesizer?

From: Ville Voipio (vvoipio_at_kosh.hut.fi)
Date: 01/03/04 

Date: 03 Jan 2004 12:11:55 +0200

russ@sotainstruments.com (RussT) writes:

> ***Yes, I did come across this! OK, can one program a PIC in a similar
> fasion? Even though the PIC is slower, could it yield acceptable
> results...perhaps 1Hz-20kHz in 1Hz steps? If not then I will bite the
> bullet and use a DDS.

A few points:

- with the variable rate interrupt system, you can make a low-jitter
  square wave without loading the processor very much (see the
  previous thread)

- for the 20 kHz repetition rate, you'll have 200 clock cycles at
  4 MHz clock. With a PIC this means 50 instructions, which should
  be just possible. With an AVR at the same clock, you'd have 200
  cycles which would be certainly enough. Using a higher frequency
  or another processor would help (I know, studying a new processor
  takes some time and effort. It is usually worth it, though.)

- for your application: please note that LEDs are not strictly
  monochromatic. They have a wide bandwidth, and their wavelength
  varies on unit-to-unit basis and also as a function of temperature.
  If you need a narrower bandwidth, see laser diodes or RCLEDs
  might fit the bill

Good luck!

- Ville 

-- 
Ville Voipio, Dr.Tech., M.Sc. (EE)

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