Generate a sine wave using a PIC microcontroller

[Aayush13]

I am using a PIC18f6722 microcontroller and I want to generate a sine wave at 60Hz. The complier I am using is CCS C. I have the PIC hooked up to a function generator so I can see the sine wave on the oscilloscope. I want to write a code that re-creates the same sine wave on CCS C so I can output it on labVIEW.

I am new to programming microcontrollers so I am not sure where to start. Thanks.

[PCM programmer]

Do you have to use that PIC ? It doesn't have a built-in DAC. If you use
the 18F46K22, it has a DAC with 32 levels.

[drolleman]

in the example directory is ex_sine.c

[Ttelmah]

and (of course), a lot depends on what you actually want to 'do' with the resulting sinusoid.

For instance, in terms of 'power delivery', you can get a sinusoidal behaviour using a modulated PWM. However to give an actual sinusoidal waveform from this, requires hardware filtering. This is what is commonly used to simulate sinusoids for things like synchronous motors.
Choose a PIC with a DAC, and as PCM_programmer points out you can then get a 'stepped' sinusoid.
Add a better DAC, and the step sizes get smaller.

More data needed before we can really help....

[Aayush13]

[asmboy]

How much harmonic purity do you need?
How much frequency accuracy?
How much jitter can you stand?
Is this a school assignment " i did it" project
or for a " real thing" ?

[Aayush13]

[PCM programmer]

[asmboy]

Everyone who has replied to this thread - does this stuff "for real"
and the direction, suggestions and questions are all of the sort you need
to answer when doing it "for real".

What we have all been telling you is that
the choice of Pic matters.

And the specifications for the sine wave product matter in the real world.

if working with analog signals and micro controllers is to become your career -
then the things being pointed out and questions posed - will need to be answered for you to make products that work as intended.

[Arakel]

How much harmonic purity do you need?
How much frequency accuracy?
How much jitter can you stand?
Is this a school assignment " i did it" project
or for a " real thing" ?


I am interested in this for myslef. This is a real thing for me since I want to become an embedded programmer but there are serious wholes in my knowledge.

Can I make the harmonics mostly of one type with a programmable filter like crawling middle?

The frequency accuracy depends on the outisde RC filter meaning probably 1 percent standart, but for medical electronics accurate measurements I do not know how much it should be?

I do not know anything about the jitter. Perhaps it is the same as in computer systems where they use Latch registers and 95% gitter is not acceptable for me. I hope PIC use FLIP-FLOP and not latch.

I use PIC16F690 for now.

If anyone can help me make this simple project I would appreciate it.

1. Generate a signal with a microprocessor

2. Low frequency square impulse filter with a microprocessor.
Tasks needed: generate a signal with the microprocessor and put a filter

2. Descreet Furie transformation with a microprocessor

Thank you in advance!
_________________
Yo! I love learning and technology! I just do not have experience so do not be angry if I ask a stupid question about a detail! From so much to remember sometimes I forget the details in order to remember the big problems!

[asmboy]

Taking the issues one at a time.

a PIC PWM generated square wave can have jitter no worse than the scaled jitter of the PIC master oscillator - but if using the internal oscillator it might NOT be low enough for all applications

if you generate a square wave and run it through a butterworth response sallen key 2nd order low pass filter - with the corner frequency set at
F0 of your oscillator frequency - the fundamental freq is -3db down
and you will still have a second harmonic content only -6db below that.

summed harmonics through the 5th leave you with all harmonics down only -4.66db at the filter output - ( pathetically distorted

Higher order multistage filters can help but never get you a quality sine wave.
The way to make clean sine waves ( less than -40db harmonics ie 1% ) is NOT found in PIC hardware
if you want low harmonics ( like .1% or better -60db down) you MUST generate the waveform in a clean way to start.
"the way" is external components and to use the PIC to control them.
here is an example
http://www.ccsinfo.com/forum/viewtopic.php?t=53564&highlight=9833

In a medical instrument that uses this 3 oscillator system to implement a Lock In detector - i share the 8.388608 mhz PIC xtal clock and the 9833's with the
9833 clock in connected to the PIC osc out pin jitter can't be easily measured against the MO...

[asmboy]

You have a mispelling:
search the forum for :

FOURIER

not furie

[Arakel]

I wish I could say I understand all that, but I dont :D. I am not an expert, I do everything by myself.

Lets summarize:
1. To generate a precise SIN wave I need better components, perhaps DSP PIC. An external filter of Sallen Key level 2. Good external oscilator, well packed PCB so I do not have interferances.

2. I can create it by controlling external analog components with a microcontroller but by my opinion that is not good because I can do it easily with no microprocessor and that would be the SIN wave generator block.

I have a question if a SIN wave is recorded in the memory how accurate will it be produced through 8 pins or 16 pins and an external DAC?

How accurate will it be produced through an internal DAC?

I know the PWM is used for generating square impulses for controlling transitors for motors in key mode but I do not know what are the recomendations for generating a SIN wave.

Am I right so far? It will take time to review this.
_________________
Yo! I love learning and technology! I just do not have experience so do not be angry if I ask a stupid question about a detail! From so much to remember sometimes I forget the details in order to remember the big problems!

[asmboy]

[Arakel]

I know that this information is gold and I am angry that I can not understand it!

Thank you! I do not quite get the decibels, I do not know exactly how much a decibel is because it is an equesion( ratio). I think it should be something like
the higher the decibels the closer do we get to "1" meaning to the idealistic result? I guess minus decibels are from minus to the idalistic result?

So a 16 bit DAC should do the job especially if there is one specialized for SIN wave conversion( I do not know if there is one)? But it still depends on the components accuracy. I know it is done somehow now a days so I have to find how.

Should it not be 180 degrees?
_________________
Yo! I love learning and technology! I just do not have experience so do not be angry if I ask a stupid question about a detail! From so much to remember sometimes I forget the details in order to remember the big problems!