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| 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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