One power source two different ground

[clydeshere]

I'm trying to use a Theremin circuit to control a volume pedal with two LDR's controlling the volume. The LDR's drop the volume so I would like to add a boost circuit to the end of the schematic.
 
   The problem is the Theremin circuit and the boost circuit both have an affect on there grounds so when they are put together on the same power source they affect each other and almost cancel each other out.


Just Theremin part




I'm wondering if there is a way to run two different circuits from the same power source with two different grounds. Or have a way to separate them in the circuit so they don't affect each other.

[deadastronaut]

just posted with interest to see replies on this ok. curious..

[Barcode80]

try utilizing the signal ground for one, preferrably the boost. Tie the +9v together, tie the ground from the theremin to the power ground, tie the boost ground to the input jack. the input jack will be grounded to the case (assuming a metal case and standard metal jacks). the case never grounds to the power supply ground, so you should have separate grounds.

I know this works with keeping signal and power grounds separate, though admittedly not sure if this will work in this case.

[clydeshere]

Ok that was one of my thoughts but wasn't sure is it would work so tie the Boost ground to the jacks?

[Barcode80]

just one jack will do. but yes.

[Gurner]

try utilizing the signal ground for one, preferrably the boost. Tie the +9v together, tie the ground from the theremin to the power ground, tie the boost ground to the input jack. the input jack will be grounded to the case (assuming a metal case and standard metal jacks). the case never grounds to the power supply ground, so you should have separate grounds.

Hmmm....when connecting two circuits together ....you need the signal and a common reference for the signal - that'll be the ground! (else you've just got two circuits wafting about like a loose flag)... unless you want to start bring isolation transformers into play between the two?!!

[clydeshere]

try utilizing the signal ground for one, preferrably the boost. Tie the +9v together, tie the ground from the theremin to the power ground, tie the boost ground to the input jack. the input jack will be grounded to the case (assuming a metal case and standard metal jacks). the case never grounds to the power supply ground, so you should have separate grounds.

Hmmm....when connecting two circuits together ....you need the signal and a common reference for the signal - that'll be the ground! (else you've just got two circuits wafting about like a loose flag)... unless you want to start bring isolation transformers into play between the two?!!

Ahhh now that sounds more like it anyone know were I can get one of those lol

[clydeshere]

try utilizing the signal ground for one, preferrably the boost. Tie the +9v together, tie the ground from the theremin to the power ground, tie the boost ground to the input jack. the input jack will be grounded to the case (assuming a metal case and standard metal jacks). the case never grounds to the power supply ground, so you should have separate grounds.

I know this works with keeping signal and power grounds separate, though admittedly not sure if this will work in this case.

Yah just tying to jacks is a no go. Doesn't work .

[clydeshere]

Would u just tie a 9 volt transformer into the ground or would u tie it to the + and - i've never used one. and trying to google tranformers is useless lol.

[clydeshere]

Would u just tie a 9 volt transformer into the ground or would u tie it to the + and - i've never used one. and trying to google tranformers is useless lol.

Oh and also could you do this with diodes somehow? That was my other idea.

[clydeshere]

Would it be somthing like this?

http://www.radioshack.com/product/index.jsp?productId=2103994&CAWELAID=107595278

[Gurner]

Would it be somthing like this?

http://www.radioshack.com/product/index.jsp?productId=2103994&CAWELAID=107595278

Yes, it would be something like that - but just reflecting here on what you want to do - you want to use the same 9V power to both ciruits? (in that case they would *not* be isolated - eg LED derived switching transients in one circuit could bleed into the other through the voltage rail).

You probably need to outline what your problem is in more details ...becuaseyou may be trying to implement a solution that isn't necessary the best fit.

[clydeshere]

the leds aren't really the problem  they run off the proximity circuit. the problem is the proximity circuit and the boost pedals ground affecting each other.

So I'm not sure how the transformers work but if i run the ground into it then run different grounds to each circuit would that work? crosses finger!!

[clydeshere]

I'll work up a mock circuit of the whole thing tonight if i get a chance would probably help.

[jasperoosthoek]

The problem is the Theremin circuit and the boost circuit both have an affect on there grounds so when they are put together on the same power source they affect each other and almost cancel each other out.

What do you mean by 'the grounds cancel each other out'? I'm utterly puzzled by the information you supply  .

Is it true that you try to convert the proximity wah (http://diyguitarfreak.wordpress.com/2010/08/11/diy-proximity-wah/) into a volume pedal? If that is true you could have added the link. I cannot read diagrams (top circuits) but I like to read schematics (boost pic).

I don't see any problems with connecting these circuits together. They did it with a wah, why not with a volume pedal.

So the theremin part is basically a proximity sensor that supplied current to a vactrol. A vactrol is an LED and an LDR in one case: http://www.alliedelec.com/search/productdetail.aspx?SKU=980-0710&SEARCH=&MPN=VTL5C3&DESC=VTL5C3&R=980-0710&sid=46CE1F80537EE17F Try getting the proximity part to work with an LED first as recommended by the Proximity Wah link. Only then add a vactrol.

[clydeshere]

Because both circuits are using there grounds to adjust different things. The proximity circuit adjusting the brightness of the LED's and the boost circuit the volume. W
hen they are connected to the same circuit the boost stops working and the proximity starts acting weird its either on or off not a smooth off to bright slide.

I'll work on a complete circuit now but i keep getting pulled away.

But can someone explain these isolating tranformers? because that seems to be whats needed I've just never used them before?

[Gurner]

As I mentioned, if you're still going to use common 9V power, then a transformer won't isolate (becuasewith common power,  it'd still be ultimately referencing the same ground on each side of the transformer) & reading your interpretation immediately above, I don't think you're understanding the root cause...other than you think that glueing two circuits together is causing ground problems.....ground is ground (and it shouldn't stray)

Bad ground planes, poor pcb layout, small tracks, ground loops, poor quality incoming 'ground ref' etc - they're going to be the true root cause.

[clydeshere]

Well I just realized I don't have a schematic program like I thought I did. Computer crashed last month and lost more than I thought.
If it's not the ground affecting the circuits than I'm not sure what else is. All I know is that when I put both circuits on the same power source the volume pot stops working at all. and the LED's stop reacting in the same way.
so guess I'm just sticking a boost pedal after this one.

[jasperoosthoek]

So both the boost and the proximity part work fine on their own? Can you try it first with a battery and a supply or two supplies if you have them? I don't see any reason why it wouldn't work.

A wild guess is that the RF part of the proximity circuit has some effect on the boost. Can you make a photo of what you made until now? More of us are curious  .

[clydeshere]

Yah they work fine independently and I just tried with two different power sources and battery lol. I'm going to try to do a Vero outline but might have to leave in a second.