Hi,
I'm an electronics newbie and for my application it would be very helpful if I could design a circuit just from DC batteries and resistors that would output a sin wave (AC). I don't know if this is possible. Is there any circuit design software where I could specify that this is what I want and have it try and create it?
Very unlikely, without active devices, such as op amps, so download
martin
Hook up a motor-generator to the battery. Consider the resistance of the motor's winding as a resistor. Or hook up a light bulb. You will now be outputting sine waves of about 430 terahertz to 800 terahertz. That's as close as you're gonna get without electronics.
Oooh, just realized, you could hook up several hundred R-2R circuits with switches and make a R-2R DA converter. Just make the switches a piano keyboard and go back and forth as fast as you please. Advantage here is that you can also output triangle waves, sawtooth, whatever you can program into the R-2R network values.
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Such a power supply is called a Pulse Step Modulator - parts of which (the switching algoritm) are patented by ABB Thomcast. The patents should show up on Google.
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Well that requires a hell of a lot more than just resistors. My idea's better.
Try to google for "Op Amp Sine wave generator FET"
Sine waves have a repetition-time characteristic, so a scheme that outputs sine waves has to have some element with the measured quality of time, or some elements whose measured qualities include time in some combination. A battery has voltage, V, characteristic, which has the units of energy divided by charge (E/Q). A resistor has (by Ohm's law) a character given by V/I, or E/(Q*I). No time t here. One possibility is to note that I has units of Q/T (charge divided by time), BUT the only bucket of charge you have is the full battery capacity.
So, the only easy time constant is the one that comes from totally discharging the battery. You don't get multiple cycles of a sine wave that way, just one quarter-cycle...
Until 1962, that was the best answer to this question. Brian Josephson came up with a scheme that year which uses universal constants (Planck's constant and electron charge) with the right units to get a voltage- driven oscillator. This is the AC Josephson effect (he got the Nobel prize). It's not simple to build (requires low temperatures, superconductors, etc.) but it's VERY cool.
Practical sine-wave generators include DC motor turning AC generator, and crank handle linked to variable resistor (as long as you turn the crank, there's AC), but to get to no-moving-parts generators you need capacitors or inductors or some other kind of circuit elements that have frequency-variant conductance. The common solution is a Wien bridge oscillator, similar to the design that launched David Hewlett and Bill Packard's little garage-shop operation.
The amazing thing about this design is that the perfect frequency control left the other variable (sine wave amplitude) completely loose. The addition of a light bulb allowed a filament-temperature variable that controlled the amplitude of the oscillation while being too slow in its variation to interfere with the AC oscillation.
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