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Very slow quadrature generator

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bd139:
3Hz is pretty fast. Should be able to do this with a simple analogue quadrature oscillator. need decent quality, large film caps though.

Ian.M:
The problem with a 3Hz analog oscillator is amplitude stabilisation without clipping or excessive harmonic distortion, and the time it will take to initially stabilise.   If other lower frequencies are required it becomes even harder.   The various digital synthesis options will be stable almost immediately after power on.   Also, for the radial (amplitude) modulation, its almost certainly going to be far easier to obtain a linear response with multiplying DACs , rather than analog multipliers.

Wolfgang:
Use an 8-Pin PIC and do it via PWM.

Ian.M:
Possible, but then you are back to needing analog multipliers for the modulation, as the max PWM frequency with adequate resolution is too low to make direct modulation of the PWM (via an analog SPDT switch per channel) before filtering viable at more than a few KHz.

Wolfgang:
Depends on the filter and the PIC clock rate. And if you think of a scope screen (1% accuracy maximum) its not so challenging.
If you want something better you could use an 877 PIC and do an R2R-DDS on two output ports, plus filtering.

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