converting line level audio to resistance?

I need to take a line level audio signal and convert it to resistance in the range between 0 Ohm and 1 MOhm. Is this difficult to do for a beginner in electronics?

Reply to
Mad Scientist Jr
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Well, zero ohms is the tough part, but even tougher than that is
having to cut and paste and repost or retype and repost earlier
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Reply to
John Fields

Well, so far you seem to be getting responses that, while perhaps relevant, might not be helping you solve your problem.

That might be partly because doing what you suggest is a bit unusual, and it might be that you are approaching whatever broader problem you are trying to solve in the wrong way. So if you tell us what you're trying to do, that would help.

But to answer one thing I think you might possibly be asking: if you mean that you want to create a device that has an audio line level input and an output that behaves like a resistor whose value varies predictably with the input voltage, yes it can be done but it is challenging. The hardest parts are getting it to be linear (or logarithmic or whatever you're aiming at), and getting it to be fast enough to deal with audio frequencies. (And as others pointed out, the 0 ohm part is impossible; you might be able to get

10 ohms, or maybe even 1 ohm, but 0 is physically impossible.) Think in terms of using the input voltage to control the drain-source resistance of an FET.

There are a lot more aspects of this you'll need to specify in detail in order to get a more useful answer.

Reply to
Walter Harley

It's not entirely clear to me why a responder would want or need to cut and paste, but with modern software it's arguably easier than having to dig for a post that mysteriously disappeared because you marked it "read" in some other newsgroup. Which is why some folks prefer multiposting to crossposting.

Reply to
Ol' Duffer

I read in sci.electronics.design that Mad Scientist Jr wrote (in ) about 'converting line level audio to resistance?', on Mon, 19 Sep 2005:

Not difficult, just impossible. Now say what you are really trying to do, and we may be able to help.

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Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
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Reply to
John Woodgate

With a name like Mad Scientist I'm sure it's right up your street ! ;-)

Graham

Reply to
Pooh Bear

V = I*R

therefore R = V / I

So all you have to do is divide the voltage by the current.

Graham

Reply to
Pooh Bear

"Mad Scientist Jr" a écrit dans le message de news: snipped-for-privacy@g44g2000cwa.googlegroups.com...

Just convert all the possible line levels to 1K.

Plain easy, even for you.

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Thanks,
Fred.
Reply to
Fred Bartoli

I basically want to control a video game (Atari 2600 paddle controls are 1 MOhm pots connected to 5V DC) with my stereo.

See "paddles"

formatting link

I don't think it has to be zero ohms exactly but a low amount.

Thanks

Reply to
Mad Scientist Jr

That's an interesting idea - how would you get the circuit to max out at 1 MOhm and at a minimum, go to as close to 0 ohms as possible?

Reply to
Mad Scientist Jr

I'll just end this subtopic and say I was a dumbass and multiposted by mistake - I posted and then had a 2nd thought "maybe it would be better in .design instead of .misc" and posted there too. Sorry for the inconvenience.

Reply to
Mad Scientist Jr

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You seem to have missed the point, which is that If I respond to a
post in, say, seb and then, later, find that identical post in sed
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Reply to
John Fields

I'm not clear whether you want the resistance to be related to the envelope (average volume) of the signal, or to the instantaneous voltage.

Are you trying to make something like an oscilloscope, to display something like a Lissajous pattern (ever-changing squiggly thing that shows phase and frequency relationship between two channels)? Or are you trying to make something that just moves the paddles depending on how loud the sound is?

If the former, you're probably out of luck; I don't think the Atari itself will respond to paddle movement at 20kHz.

If the latter, then Rene's light bulb idea is not a bad one. One problem is that light-dependent resistors (LDRs) with 1MEG dark resistance are usually pretty slow, taking as much as several seconds of darkness to get all the way to 1MEG. The resistance will go low in a hurry, but it takes a long time to recover to high - it's sort of like your eyes when they dark-adapt.

Either way, you probably only need a current or a voltage, not a resistance. That's considerably easier. And I wouldn't worry about getting the (effective) resistance any lower than 1k ohms, since the pots in the joystick are almost certainly linear (as opposed to log-taper): the difference between 1k and 0 is 0.1% which is less than the pots themselves can distinguish.

Give Rene's idea a try, as a start. If it doesn't work you can evolve it.

Reply to
Walter Harley

Maybe it's this damn google groups interface, you click Reply and assume it is quoting the original article and then it doesn't

let us know what you're responding to then we won't have to digging for it.

Reply to
Mad Scientist Jr

That sounds easy, I will need to multimeter it.

2 dangers:

1) blowing up the stereo if the output resistance is not 8 ohms (or whatever the output expects for headphones) - that's why I originally said Line Level, this would be a single standard as opposed to different stereos which need different resistance speakers.

2) blowing up the video game - it sends 5v out and measures how much of that comes back. I assume the signal from the stereo sends voltage as well. So what happens when you have the 5V from the game, plus the volts from the stereo? What if the game can only handle at most the 5v it is sending out? Therefore, I would rather make a circuit that 1) controls resistance 2) provides some attenuation so the stereo doesn't blow up

on with your life...

The way your pots are connected suggests that your game is already voltage driven, so you would only have to amplify your audio to cover the 0-5V range. For starters try connecting your audio output directly to the paddle pin (and gnd to gnd) and see what happens.

Foo,D

Reply to
Mad Scientist Jr

The latter would be easier and would probably do the job, but the oscilloscope version would probably be more interesting. If the circuit could take the frequency (say 0 Hz - 20,000 Hz) and find the equivalent fraction within the Atari's range (1k ohm thru 1 MOhm), then it would be able to convert it to paddle movement the Atari will recognize.

Reply to
Mad Scientist Jr

If you are going to connect the line level voltage to replace the paddle , then you will not use the 5V connection. The voltage reference will be the audio ground. Just in case it hasn't been mentioned, it would be a good idea to put a diode in the circuit path to assure that only a positive voltage is applied. You can protect the input further, by putting a 250k or

1 Meg resistor in series with the audio - Atari connection. For protection, start with the high R and reduce to a lower value if more current is needed.

Don

Reply to
Don Bowey

"Ol' Duffer" a écrit dans le message de news: snipped-for-privacy@news.bright.net...

IOW, you're begging for some information and you think others have to suffer the inconvenience you create just because you don't want to bother being careful enough?

How selfish you're.

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Thanks,
Fred.
Reply to
Fred Bartoli

Fair enough, I have to digest all this and I have some reading to do.

Thanks to you and everyone for your replies.

  1. John Woodgate Sep 20, 12:00 pm show options

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Reply to
Mad Scientist Jr

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John Fields

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