converting line level audio to resistance?

--- 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 replies because a querying poster (you) didn't crosspost to all the groups where the question was presented. Your newsreader has a box where you enter where you want your post to be sent, and if you fill in all the groups where you want it to go the first time you send it, it'll be sent to all of them automatically and then anyone reading your post in any of those groups and replying to it will send replies to all of the other groups as well. That's called "crossposting" and makes life a little easier for us all, so why not try it?

-- John Fields Professional Circuit Designer

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

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

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.

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.

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

Graham

V = I*R

therefore R = V / I

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

Graham

"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.

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"

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

Thanks

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?

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.

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.

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.

That sounds easy, I will need to multimeter it.

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.

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

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.

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

Don

"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.

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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