# multiple voltages from single power supply?

Hi guys.

So I'm working on building an arduino guitar-pedal. And I've got the output working (from Instructables).
Now the same author have made a tutorial for an audio input for the arduino (offsetting the signal so there is no negative signal going into the arduino) Now in this tutorial it says that you need 2 9-volt batteries in series (the middle to ground) to generate the positive and negative 9 volts for an op amp.

My problem is I really don't want to use 3 of my power-suppy outtakes to power a single pedal.

I've read something about voltage splitters, and it seems that maybe they could bring me down to 2 outtakes...

Can anyone point in the right direction? Or just tell me once and for all that it cannot be done?

boiled down: I got 9 volts coming in, and I need power for the arduino and +/- 4.5 volt for an op amp.

The analogue inputs of an Arduino are high impedance.
Just what an electric guitar wants.
And the electric guitars I know have enough voltage swing.
Just what an Arduino analogue input needs.

I don't see the need for a preamp.

Make a voltage divider with two 2.2Megohm resistors.
One from the 5volt pin to the analogue input, one from the analogue input to ground.
Couple the guitar signal to the analogue input via a 100n capacitor.
Leo..

It seemed strange to me that I would need 2x9v batteries.

Thank you.

And so the testing and cursing begins.

Or get one of these:

.

The project seems to use a microphone.
A preamp is needed for a microphone signal, but not for a guitar signal.
Leo..

Perfect. Thank you very much mate. I was going nuts... and also going the wrong way.... Sucks to be a n00b. Should have started years ago. Thankfully there's internet and forums.

I agree.. With a guitar you shouldn't need an op-amp.

Just for future reference -

It seemed strange to me that I would need 2x9v batteries.

It's usually easier (and often better) to run an op-amp from positive and negative voltages. The cheapest & easiest way to do that is with 2 batteries.

Now in this tutorial it says that you need 2 9-volt batteries in series (the middle to ground) to generate the positive and negative 9 volts for an op amp...

...and negative 9 volts for an op amp.

...and +/- 4.5 volt for an op amp.

That's confusing and I'm not sure what voltages you really need. I assume You are not using +/-4.5V supplies, but a 9V supply and a virtual ground at 4.5V.

If you need +9V and -9V, that's two batteries (not 3). The Arduino has a voltage regulator so it can run from the same 9V battery as the +9V power for the op-amp.

Now the same author have made a tutorial for an audio input for the arduino (offsetting the signal so there is no negative signal going into the arduino)

You can do similar things with an op-amp to run it from a single supply.

[

My problem is I really don't want to use 3 of my power-suppy outtakes to power a single pedal.

If you've got something like [u]this[/u], the outputs probably have common grounds so you can't get -9V or connect the outputs in series.

You can do similar things with an op-amp to run it from a single supply.

I've found a circuit for that. But that seemed to flip the signal upside down... And that could cause a problem I think with phasing (example using 2 amps or am I wrong again?) then I would have to flip it again (maybe in the code, which would cost a little time)

If you've got something like this, the outputs probably have common grounds so you can't get -9V or connect the outputs in series.

I have a "Big John" 6 outlets in 3 isolated circuits... But I don't think that I was ever going to use 2 (you're right. of course the arduino could run on the same as the positive side of the op amp)

But I'll try the way Wava suggested.

Thank you.

First: Every section of an Op Amp MUST be connected. Leave it floating, it may burst into oscillation or latch up and burn out the Op Amp.

Use a different Op Amp that can run from 5V. Put the DC blocking capacitor at the input.

What difference do you think it would make if the signal were inverted?

What difference do you think it would make if the signal were inverted?

I was thinking something like if I'm recording, and I had the dry signal going through one amp, and the wet signal (the inverted signal from my pedal) going through another amp, that they would kinda "cancel each other out" ? not sure... just seemed weird to have a signal going the wrong way. Is this a normal way to do it?

(On the diagram) Thank you. But I don't understand what it does exactly... Can you recommend some reading or youtube videos? I would like to learn stuff so I won't have to continue copying stuff.

PDF

.

LarryD:
There is so much out there on the internet and youTube.

Yes there is, but there's also tutorials for doing brain surgery in your garage, over-unity power generation, making laser guns, anti-gravity.......

Sure, it's easy enough to just see the titles of those and chuckle, but then there's also the op-amp tutorials by someone who uses "that 'should' be good", and "no need to worry about the smoke", and " it's supposed to smell that way".

"Yes there is, but there's also tutorials for doing brain surgery in your garage, over-unity power generation, making laser guns, anti-gravity......"

How difficult is it to read a few paragraphs to see if a document is beyond you?
60 seconds?

A person should be able to put some effort into their own education.

When you don't understand something you can ask for assistance.

.

I've been using the "filetype:pdf" a lot in Google.
But a lot of books seems good and understandable at first, and then many pages in, I think to myself "wtf am I reading?"

Good point, if you are using the signal before and after to drive 2 amps/speakers.

Info on using Op Amps on a single supply voltage:

http://www.ti.com/lit/an/sloa030a/sloa030a.pdf

These are from manufacturers, not from someone's ill-thought-out Instructable.

Again- every unused section MUST be properly connected. Do NOT leave inputs floating. Follow proper procedure.

BTW, you can always invert the signal in software to compensate for an inverting preamp.