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I have made a Chua's circuit that is nearly the same as the one in Kennedy 92(pdf). I don't have an oscilloscope yet, so I connect a DC voltmeter at the place where probes of oscilloscopes should be connected to. From my understanding, the current in the circuit should be alternating current, since the "double scroll" pattern is symmetrical about zero (it is a nonlinear oscillator).

The DC voltmeter only measures the average voltage over a short time period, something like 0.1 seconds. So it should show zero reading if it is connected to an alternating current.

However, when I actually do the experiment, no matter how I adjust the value of R(see diagram), the reading of the voltmeter across C1 never gets to zero. I know that for some values of R, the p.d. across C1 is not alternating. But for the double scroll to appear, average p.d. should be zero. enter image description here

However, for values of R less than 1000 Ohms, the p.d. across C1 is quite small (about 0.2V)

Does that indicate that there are something wrong in the circuit, or is my understanding above wrong?

Or are the information above insufficient to draw any conclusion?

Jethro
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    If you try to use a device designed to do task A to do task B the result may be useful, or useless or dangerous or ... . A DC voltmeter is designed to measure DC. If you attempt to measure AC the assumptions that you make and those of the designer may vary. – Russell McMahon Jul 17 '19 at 10:57
  • As a converse example, many lower cost DMM's when used to measure a DC voltage on an AC range produce an "AC" reading about double the DC voltage. eg a voltage of 2.5VDC would read as about 5VAC. I have never looked at the circuitry but imagine that they may half wave rectify the input, smooth it and apply a scaling factor that gives a proportionate DC voltage. When used with DC the voltage is present for a "full cycle" and so reads twice as high. – Russell McMahon Jul 17 '19 at 10:57

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Your voltmeter is probably showing DC offset because depending on how you built your Chua's circuit (and what it is doing at the moment) it will have a DC offset.

From your linked document:

enter image description here

It looks to me like a properly operating Chua's circuit can have offsets in various directions.

Outside of that, your circuit may be operating incorrectly (or not at all.) You really need an oscilloscope to see what is going on.

If your Chua's circuit is supposed to operate at audio frequencies, you can get a free oscilloscope program for your PC (or smart phone) and have a look. You'll probably need to add in a bit of circuitry to match signal levels and your audio input, but that should be easy enough to do - the software producer and the internet in general has a lot of info on "sound card oscilloscopes."

Jethro
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JRE
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  • Thank you. There is one unclear point though. "showing DC because depending...". Do you mean "showing DC **offset**" here? – Jethro Jul 17 '19 at 12:08
  • I dont think you will be able to see any DC offsets with most sound cards. – Rokta Jul 17 '19 at 12:31
  • @Rokta: That's true. But, you will be able to see if the Chua's circuit is doing something or just sitting there dead. From the given measurements (DC,) you can't tell if it is even oscillating. A sound card scope would at least show you that. – JRE Jul 17 '19 at 12:34
  • @JRE So sound cards will just translate the signal to the origin and will not do anything else? I am a bit worried whether the soundcard will work. – Jethro Jul 17 '19 at 22:31
  • @Jethro: A sound card will at least let you see if the circuit is oscillating. Assuming that the circuit operates below 22kHz, that is. – JRE Jul 18 '19 at 05:36