[sdiy] XR2206 temeperature stability within +/- 5%

[Gordonjcp]

On Thu, Jul 02, 2020 at 10:29:24PM +0100, Richie Burnett wrote:
> Have you thought about doing this digitally with a low-end micro? You didn't say how pure you need the sine wave to be, but you could generate it by PWM. (You can filter the hell out of something that only needs to go up to 60Hz maximum and doesn't contain any harmonics.)
> 
> The very low maximum frequency spec is amenable to software DDS with PWM output, provided the purity spec isn't ridiculous. 

This is a good if slightly outdated article (the syntax for storing data in program flash has changed a bit):

http://interface.khm.de/index.php/lab/interfaces-advanced/arduino-dds-sinewave-generator/

Follow that up with a decent low-pass filter and you've got a pretty reasonable sine, maybe not quite up to the cleanliness required for distortion analysis.

I've had excellent results using a Sallen-Key filter using a single-transistor buffer at about 15kHz with a notch filter centred around the 31370Hz (doesn't need to be accurate!) PWM frequency.  If you really wanted to remove any steppies then you could lower the cutoff of the lowpass to something not much above your desired maximum frequency.

-- 
Gordonjcp