Noise bleed-thru on shared power supply

I have an Arduino generating LFO and voltage sequences through a vactrol to an analog filter.

When I have the analog filter on its own 9v power supply, and the Arduino powered by USB, it is great: silent, zerp bleed-thru from the digital side to the analog side.

When I share a power supply (9v supply to analog filter and to Arduino board) the bleed-thru is huge, especially when sending PWM out.

Are there any known ways to fix this other than going with two isolated power supplies?

Thanks (I'm pulling what's left of my hair out over this one)!

Hi Beavis,

Hmm.... Need more data: Why a vactrol? What are you trying to isolate? Bleed-through of what?

How about a schematic. If you can't draw one and host the picture somewhere, try using this http://www.sigsoftware.com/emaileffects/ software to draw an ASCII diagram.

Regards, David

Hi Beavis,

Hmm.... Need more data: Why a vactrol? What are you trying to isolate? Bleed-through of what?

How about a schematic. If you can't draw one and host the picture somewhere, try using this http://www.sigsoftware.com/emaileffects/ software to draw an ASCII diagram.

Regards, David

The vactrol is used to control the analog circuit, not for isolation per se.

I guess I'm looking for general ideas about how to prevent bleed-thru of signals from the Arduino and an analog circuit that share the same supply.

Not an “answer”, but perhaps germaine…

I once wrecked a number of PICs as follows… never did figure out how…

I had a mains-to-unregulated 12v transformer.

From that, I interconnected the ground (0v) pins of…

a) an LM7805 unreg->regulated 5v PSU, on my PIC’s pcb, similar to the circuits on my Arduino and clones.

b) the 0v side of an “H” controller feeding the 12v to a model train (DC motors) layout.

From my PIC, I passed PWM outputs through opto-isolators to the +ve side of the “H” controller. I put “short out collapsing field spikes” diodes, like the standard one we put across a relay’s coil, everywhere I could think to put one.

Still managed, several times, and usually almost immediately, to fry my PICs.

If I powered the trains with a separate transformer, all was well.

Apologies for not having more complete details. Any thoughts welcome! I.e. “Did you remember to…?” stuff…

Tom

Without a schematic we're shooting in the dark. Duck.

Our engineers spend more time on that problem than any other problem. You'd be amazed at all the hoops they jump through.

The power input to the analog filter should be run through a filter. Also filter the power at the input to all your sensitive devices with bypass capacitors.

http://www.allaboutcircuits.com/vol_3/chpt_9/1.html

http://www.maxim-ic.com/appnotes.cfm/an_pk/883 http://www.maxim-ic.com/appnotes.cfm/an_pk/899

Bypass capacitors http://www.allbusiness.com/electronics/computer-equipment-computer/6240814-1.html