"The ideal design has zero parts."

Here's what I've done to get RMS on a PIC:

With an interrupt, square the current 8 bit sample (16 bit result) and add
into a 24 bit sum. Increment a counter.

When you have 256 samples, divide by 256 (throw out 8 lsb), then take the
square root. That's the RMS. Clear the sum and the sample counter.

This techniques was used in a pic based voltage regulator in a curing
light for dental composites.

Harold



> Why not use an RMS converter such as the AD736
>
> Brian.
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Tan Chun Chiek
> Sent: 21 November 2003 14:30
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE:] Sine wave to DC conversion
>
>
> RMS
> ----- Original Message -----
> From: "Wouter van Ooijen" <wouter@VOTI.NL>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Friday, November 21, 2003 9:24 PM
> Subject: Re: [EE:] Sine wave to DC conversion
>
>
>> > Yes, I'm trying to get the average DC level, the RMS value of
>> > the sine wave.
>>
>> Which of the two, or both? The average of a sine is zero, the RMS is
>> sqrt(2)*((1/2)*[top-top])^2.
>>
>> Wouter van Ooijen
>>
>> -- -------------------------------------------
>> Van Ooijen Technische Informatica: www.voti.nl
>> consultancy, development, PICmicro products
>>
>> --
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