Sine wave

[Darrenmac]

Thanks Daryl,
I will give it a go when I get a spare hour. One concept that I had completely overlooked is the fact that the outputs go low (silly me). I was only calculating using the hi 5v state and not the low 0v (GND) state which will completly change my calculations.
Thanks, I will let you know how I go

[Darrenmac]

Daryl,
I had a go using your data and got the same result (not what I was hoping for a sine wave). I decided to increase to 6 bit and have another stab at it. I got the same triangle wave that you had on your example. (still not the expected sine wave). I then divided 180 degrees down to the same number of samples, used the sine function, added 1 (then no negative voltages), and scaled to same as actual voltages. I had a new set of data that I used to base my output on. essentialy I picked the closest actual value to the calculated value. I graphed the new data and got the attached waveform (more like a sine wave). This was acheieved by repeating some of the samples with the same voltage and on some skiping voltages. Now I am not sure how the best way to implement it is? do I create a table using this data and simply step through? or do I use the sine function in the pic basic to calculate the output?

[Darrel Taylor]

The SIN function will be the easiest.
It's what the FREQOUT statement uses to generate its sine waves.

It's essentially a pre-made lookup command. So it'll save you some work.
The result is an 8-bit number so you could just shift right twice and have your 6-bit value. But 8-bit would be better at such low frequencies.

You may also want to look at this from sirvo ...
http://www.picbasic.co.uk/forum/show...5843#post65843

I've pointed to the video of the finished project, but further up you can see how he did it.

It uses a lookup, and 10-bit PWM (with 8-bit values) instead of R2R.
I wish I had a scope like that.