Voltage subtraction.

[123edsaq]

Hi,
I have a 5V DC supply and a 5V sine wave(5V +ve, 5V -ve). I figured that if I put these two supplies in series, I'd get a 0V to 10V sine wave (not tried it in real life, just on a simulator)

Now, suppose I just have this 0-10V sine wave, and I want to bring it down to +5V and -5V, how can I do it ?

That is, if the voltage at any time is V, I want an output voltage of (V-5). So if it's 2 V, it should output -3V and if its 7V, it should output 2V.
Is this possible ? Any ICs that do something like this ?

Thanks

 

[poor mystic]

Hi
there are several ways to do this.
First, I'll mention op-amps in a summing circuit, then I want to point out that a capacitor can do the job, and finally I'll point out that transformers are sometimes used for this kind of work.
It all depends what application you have in mind.
If you want more details, say what you'd like to know about!
Mark

 

[123edsaq]

Hi, thanks for the response!
Actually, I'm actually trying to figure out (without just mindlessly googling and then assembling stuff--so that it is a learning experience) how to transmit an audio signal from one micro-controller to another one.
And while I know that this probably can be done 500% more efficiently, I wanted to try this idea out never the less (I have little experience with analog electronics so tell me if it is incredibly stupid please):
-I saw on my scope that my audio signal reaches peak voltages of +2V and -2V, so I thought I could make this a 0-5V signal by putting it in series with a 2V source.
-I'd then take this 0-5V signal through an ADC and transmit the data digitally.
-When it reaches the other end, I wanted to pull it out through a DAC (an R-2R ladder because that's all I know of) and then return the waveform to it's original voltage levels (-2V,+2V)

I'm pretty sure this method is neither standard nor efficient (and probably not possible) but I still want to try it out and see what results I get.

 

[poor mystic]

I see.
Not stupid at all, but not really very practical either.
You could do it this way... there's nothing wrong with the theory as far as you've applied it, and I very much appreciate your idea of learning by doing and thinking about the results. But, I don't think you'll be satisfied with the outcome of your research methodology, because you don't have a thousand years to learn electronics, man gets only three score plus ten, you get my drift?

I have a book in front of me: "The Art of Electronics", 2nd ed, Horowitz and Hill.
ISBN 0 521 37095 7. It's a great read, and the best book on electronics that's ever been written. I suggest you get a copy for yourself. Immediately... you'll never look back.

I almost wondered whether I should not say the following, but I'll just warn you that it's good advice and that way you can choose not to read it at your pleasure.

The usual way to do the job would be to power the ADC from a dual supply. This allows the signal to be directly encoded, so avoiding the noise and general hassle and expense introduced by the op-amp or whatever you'd otherwise use.
I'd like to give you a better, deeper response than this btw but whatever direction you shake a stick there are a dozen methods you could use to get around the problem and for every one of those methods, usage 'depends'.

So, get that book, don't look back, and whenever you want, ask whatever you want to know about, here in the forum.

Mark

PS: there is no last word in this game. It all "depends" and it is all subject to review.
Oh, and: I am liable for nothing!!!

 

[123edsaq]

I was afraid it would boil down to just that. I learned just about everything I know about microcontrollers using a datasheet, trial and error and time to spare and I was hoping to do the same here..

Thanks for suggesting that book, I'll get a copy and see if I understand the stuff in there (I only have a background of microcontrollers and programming)

In any case, I'm most likely going to end up back here with questions !

 

[poor mystic]

Fear not. You'll understand it no trouble. That's what makes it such a great book!

 

[123edsaq]

Oh man, I wrote out a PM to you, but it turns out I need a post-count of 15 before I can send it !
I guess I could just post it here:

Turns out my brother bought the book and left it here(I have the 2nd ed too). I found it, but I'm really not 'too keen' on reading all 1100 pages.

Of all the listed stuff, I only know most of the first chapter (learned it in school). While I'm familiar with a lot of the other stuff, I don't know the math of anything.

Do you think you could point out which topics/chapters would be of interest to me (wrt to my forum post) so I can concentrate on understanding everything that leads up to that first instead of reading everything and not figuring out just what I was looking for ?

Thanks a lot.

 

[poor mystic]

OK, what about making sure you understand everything up to page 250. That'll give you a foundation and when you want more, go back to the book.
You can always skype me. Set up a contact request today if you like and I'll approve it so that when we want to text chat we can.
Skype name is poor.mystic
Mark