power supply questions

I'm using an arduino in a stompbox to control an analog circuit via an optoisolator. I do not want the analog and digital circuits to share ground since I've found that introduces noise even with extensive filtering. However, I still want to be able to run everything off of a single 9v power supply.

First of all, I assume I'll need one of these on the Arduino side: http://www.sparkfun.com/commerce/product_info.php?products_id=107.

Second, how do I keep the grounds seperated? Obviously, all of the circuits wired to a multi-pedal power supply are not sharing ground, but is there anyway to do this without adding a heavy and bulky transformer to the box?

Thanks, Zach

I still want to be able to run everything off of a single 9v power supply.

If there is only one supply then you have to use a common ground and there is little point in using an opto isolator.

Otherwise you need a septate supply on each side of the opto isolator.

I'm using an arduino in a stompbox to control an analog circuit via an optoisolator.

Any more details? Are you passing digital signals? analog signals? How much current does the analog circuit take? Does it need 9V or 5V?

You could use an isolated DC/DC converter module to take 9V from the primary side and pass the power to the secondary side with isolation. The details, of course, are how much power you need (hence the questions above):

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=445-2452-ND

http://www.ruggedcircuits.com

The analog cuircuit needs 9v. As mentioned, the only communication is through the optoisolator. No signals, digital or analog, are passed. I figure I could use some type of small transformer and then that voltage regulator to knock it down to 5v on the Arduino side. I'm curious as to how that circuit from digikey achieves isolation.

As mentioned, the only communication is through the optoisolator. No signals, digital or analog, are passed.

Errrr....what does it pass across the isolation barrier then? Good wishes?

I'm curious as to how that circuit from digikey achieves isolation.

It's a switching regulator, probably flyback topology:

http://www.national.com/appinfo/power/files/f5.pdf

http://www.ruggedcircuits.com

Well, I'll be sending PWM to the LED side.

I haven’t drawn up a schematic yet. It’s just something I’ve breadboarded. It uses two CMOS chips (4093 and 4049) powered off a 9v battery. The only connection to the Arduino is through an optoisolator. All I need is a way to get two 9v power supplies with isolated grounds from a single 9v AC adapter. I don’t see how the circuit matters at all.

All I need is a way to get two 9v power supplies with isolated grounds from a single 9v AC adapter.

Read my lips. You can't.

OK just for completeness you can do it if you run two voltage inverters with 1:1 transformers from the supply. But your switching noise is going to be much worse that sharing a ground. Your circuit matters because we can't see why you need isolation here, you should not need it.