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mosquito56
07-03-2009, 11:10 PM
·Can I hook up a breadboard with a power supply to a demoboard with a power supply and have them both turned on? I am thinking as long as they have a common ground it is ok?
· I have never tried something like this and thought it better to ask first.

breadboard is run on 7v battery
demoboard is run on 9v wal wart.

I am wondering about reverse currents.
Thanx
Don

Post Edited By Moderator (Joshua Donelson (Parallax)) : 10/23/2009 4:52:41 AM GMT

Mike Green
07-03-2009, 11:26 PM
What do you mean by "reverse currents"?

Hooking up two sections of a device, each one powered by a separate power supply, is done all the time. Mostly you need a common ground.

mctrivia
07-03-2009, 11:28 PM
Connect the grounds but not the positive side. Will work for communication between both.

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mosquito56
07-03-2009, 11:33 PM
I seem to remember "reverse currents" from biloxi in the early 70s concerning power supplies running from high voltage to low·voltage.

If 5v reg on board 1 runs at 5.23 v and board 2 runs at 5.6 volts you will have current flowing from high to low. Also from connecting 2 batteries in parallel and one·of them going dead, draining the second. I seem to remember a diode to prevent this.



If you say I can do it, that's good enough for me. thanks again·Mike.



Don

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······· "What do you mean, it doesn't have any tubes?"
······· "No such thing as a dumb question" unless it's on the internet
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Mike Green
07-03-2009, 11:46 PM
"If you say I can do it, that's good enough for me"

Common sense and a basic knowledge of electricity, Ohm's Law, Kirchhoff's Law, etc. is much better.

en.wikipedia.org/wiki/Ohm's_law (http://en.wikipedia.org/wiki/Ohm's_law) and en.wikipedia.org/wiki/Kirchhoff's_circuit_laws (http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws)

mctrivia
07-03-2009, 11:49 PM
If the positives are not connected that will not be an issue. That is the reason redundant power supplies need to be connected by dioiodes.

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propmod_us and propmod_1x1 are in stock. Only $30 (http://propmodule.com/?x=products). PCB available for $5

Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd (http://www.gadgetgangster.com/160) and propmod-1x1 (http://www.gadgetgangster.com/161) are now available for use in your Gadget Gangster Projects.

Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com (http://uploader.propmodule.com) for free.

Loopy Byteloose
07-03-2009, 11:56 PM
The topic of 'reversing currents' is but one issue. The other is known a 'ground loops'. Try Wikipedia for an explanation.

In theory, you establish one common ground at the power supply and that should b enough. I stacked 3 Propeller ProtoBoards and have additional ground connections, so I worry about ground loops causing trouble, but so far I haven't had any. So until I run into a problem, I won't remove them. I doubt that they will do any damage even if they cause a problem. The amount of power involved is quite small.

One can put a blocking diode before the barrel plug going to each board if the power supply has ample voltage to manage the 0.7volt drop. That should prevent any reverse current on the high side, but it may be unnecessary. The truth is that you can junk up a nice working design with a lot of extra engineering. Since both boards have a regulator that sees the power first, the 'reverse currents' would be between the two power supplies and only if their high sides were connected - not a good idea.

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Ain't gadetry a wonderful thing?

aka G. Herzog [ 黃鶴 ] in Taiwan

Post Edited (Loopy Byteloose) : 7/3/2009 4:07:25 PM GMT

mosquito56
07-04-2009, 12:13 AM
Thanks for all the input. It doesn't matter now, since I can't get the breadboard cuircuit to work.

······· I am trying to get a new op amp working and cannot get it to work. I've soldered the darn thing to the board and didn't want to desolder it so I put another one on a breadboard to try to get it to work. Can't get that one to work either.

· The spec sheet shows one drawing for about 10 different chips. I am using the lm324n which is a quad amp. I am wiring it in the simplest form. 1 meg thru 10k pot which is the same they show on the spec sheet.



· I have·been using lm358 for months with no problems. Wired both chips the same, Nothing.

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······· "What do you mean, it doesn't have any tubes?"
······· "No such thing as a dumb question" unless it's on the internet
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