[sdiy] oscillator auto calibration

[Needham, Alan]

Assuming the PIC I/O pin will be calling an interrupt routine :-
As this will involve an undefined (and variable) response delay won't you end up trading one error for another ?
Also, if this kind of accuracy is important, what will be the PIC chip's timebase, a 100ppm crystal with its own temperature drift problems, the XR2206 claims 20ppm/C anyway ?

Maybe discrete logic could be a better idea for the control loop but I still wonder about a solid timebase.
Sorry if I am mis-interpreting your intentions here but, as interesting as the idea is it seems a bit loose to me!

	Alan

>-----Original Message-----
>From: synth-diy-bounces at dropmix.xs4all.nl
>[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of
>jean-pierre.desrochers at ville.quebec.qc.ca
>Sent: 08 May 2007 1:50 PM
>To: synth-diy at dropmix.xs4all.nl
>Subject: RE: [sdiy] oscillator auto calibration
>
--edit--
>Here is the trick:
>CV voltage 0-5VDC going to the 12 bits Pic ADC,
>The Pic reads the AD value and goes to a serial EEPROM
>lookup table at that AD address to fetch a 16bits 'period value'.
>The XR2206 freq (square wave) is sent back to one of the PIC I/O pin.
>If the XR2206 freq is too low or too high according to the lookup data
>(at the specific CV input) the Pic send a PWM square wave
>filtered with a low pass to compensate the drift and bring
>back the CV/freq desired to the XR2206.
--edit--

_____________________________________________________________________
The information contained in or attached to this email is intended only for the use of the individual or entity to which it is addressed. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. It may contain information which is confidential and/or covered by legal professional or other privilege (or other rules or laws with similar effect in jurisdictions outside England and Wales).
The views expressed in this email are not necessarily the views of Centrica plc, and the company, its directors, officers or employees make no representation or accept any liability for its accuracy or completeness unless expressly stated to the contrary.

Centrica plc

Registered office: Millstream, Maidenhead Road, Windsor, Berkshire SL4 5GD

Registered in England and Wales No 3033654