Electronics > Projects, Designs, and Technical Stuff

Very slow quadrature generator

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Doctorandus_P:
I didn't read all posts, but I'm with Dave, the "super conductor" in one of the first handfull of posts.
Use a uC.
"Arduino" folks could probably luse PWM and filtering on such low frequencies but a uC with 2 hardware DAC's or with an external DAC is much more convenient for a few bucks / peseta's / pegels / whatever.

Something like the combined channels of a MCP4922 can reach 20 bit or so and would be plenty for smooth curves, but using the 2 channels of a single MCP4922 for X and Y is very probably good enough.

rhb:
The quadrature part is easy.  That's just a precision analog integrator which is a stock data sheet circuit.

The sine wave is harder to do with an analog circuit.  I don't know if you could get a Wein Bridge oscillator to go that low.  You should read "Max Wein, Mr. Hewlett and a Rainy Sunday Afternoon" by Jim Williams if you want to use an analog circuit.

But any number of digital approaches are quite simple to implement.

Ian.M:

--- Quote from: rhb on January 20, 2019, 02:33:02 pm ---The sine wave is harder to do with an analog circuit.  I don't know if you could get a Wein Bridge oscillator to go that low.  You should read "Max Wein, Mr. Hewlett and a Rainy Sunday Afternoon" by Jim Williams if you want to use an analog circuit.

--- End quote ---
See chapter 7 of “Analog Circuit Design” by Jim Williams.

EmmanuelFaure:
Another way without a DAC, using a delta-sigma technique. Requires only a µC with a digital output, a analog input, and a cheap RC circuit acting as an integrator.

Pseudo code :
while(1) {
if(voltage < sin(2.pi.3Hz)) {
output = 1;
}
else {
output = 0
}
delay(); <- Not mandatory. The sin() computing delay should be enough to delay the loop (On an arduino ~100µs).
}

In attached file : A simulation of the output signal done with excel.

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