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Even a Schmidt trigger, attributed to being able to create the start of an oscillating circuit, has to get its start from an AC sine wave. It seems that no amount of tubes or transistors can independently make their own trigger. This mechanism for quick switching has to come from someplace, and without anybody being able to explain it to me, the only thing I can think of that makes quick switching possible is the fact that our circuit is plugged into this wall outlet that happens to have a quick moving alternating sine wave current flowing through it. Is it possible to create an electrical circuit that only has one initiating signal (the press of a button or the presence of DC voltage, say) that can cause itself to switch based on that one signal? The only thing I can think of that can independently switch is a thermal flasher.

Neil_UK
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Jared Cravens
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    An oscillator is a device that takes constant voltage and generates a switching waveform. – user1850479 Feb 26 '20 at 02:44
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    *Even a Schmidt trigger, attributed to being able to create the start of an oscillating circuit, has to get its start from an AC sine wave*. This is not true. – linuxfan says Reinstate Monica Feb 26 '20 at 08:43
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    Somewhere in Q1 to Q7 in your previous question, there must be an astable multivibrator which does exactly that. To find it, trace the circuit with the switches in "Auto" position; at a glance I think it's Q3,Q4. Or search the webs for "astable multivibrator". –  Feb 26 '20 at 13:02
  • Much appreciated Brian, I'm working on that right now. – Jared Cravens Feb 27 '20 at 21:07

3 Answers3

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Is it possible to create an electrical circuit that only has one initiating signal (the press of a button or the presence of DC voltage, say) that can cause itself to switch based on that one signal?

Yes.

Do a Google image search for "oscillator circuit" to get all the examples you have time for. For more specific results, try "Pierce oscillator", "Hartley oscillator", "relaxation oscillator", "astable multivibrator", ...

In many of these circuits, there is a theoretical fixed operating point without oscillation, but it is unstable, so that even the inherent noise of current flowing through a resistor will eventually start them oscillating. Others are a bit harder to get started, but generally the act of turning their power source from off to on will start them.

The Photon
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  • Wow, thanks so much. The basic principal behind all of these looks to be the charging and self-discharge of a capacitor, is that correct? – Jared Cravens Feb 26 '20 at 04:34
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    That's an astable multivibrator. In others, it's more about achieving a phase shift in a feedback circuit (google *Barkhausen criterion*), but there's usually a capacitor involved in those circuits too. – The Photon Feb 26 '20 at 04:37
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The frequency of the AC voltage available at a wall socket is generally 50 or 60 Hz, hardly a quick moving sine wave considering that you can buy or build electronic oscillators at frequencies into the GHz region. These oscillators only require a DC voltage to operate. Consider the switching circuits in the microprocessor in any PC that routinely switch at GHz rates once DC power is applied. Even a simple 2-transistor astable multivibrator circuit can switch at nanosecond speeds and only requires a DC voltage (no triggering needed). Monostable multivibrators do require a trigger but that is by design. I think you need to reconsider your premise that fast switching originates from the AC mains because then you exclude all battery operated equipment such as cell phones which incorporate many high speed switching circuits.

Barry
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  • Okay, so what's an electronic component that can generate it's own switching ability, independent from any other component? Sure as hell isn't a transitor, or 100 transistors, because they can only switch when something else first switches them. I've researched oscillatiors, Schmidt triggers, Miller drivers, etc and every component or circuit is only switching based on a switching signal being sent to it. Where's it coming from? Something can't come from nothing. Where's the switching being originated? – Jared Cravens Feb 26 '20 at 03:11
  • Oscillators do not require PWM you need to sit down and process what you have read more carefully – crasic Feb 26 '20 at 03:47
  • Okay, thanks for clearing this up crasic. I'm doing a lot of reading, but sometimes it doesn't make sense, I'm which case I come here for you guys to help steer me back on course. – Jared Cravens Feb 26 '20 at 04:25
  • Congratulations for the logic thought about battery operated devices. – linuxfan says Reinstate Monica Feb 26 '20 at 08:46
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take a Schmidt ---- place an inverter after it, if needed so the chain is inverting

then place an RC delay/integrator/lowpass between output and input

depending on the amount of hysteresis, the RC tau will be approximately 1/(2*frequency)

analogsystemsrf
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