# Help with circuit layout

#### gumbright

Joined May 22, 2006
4
I am working on a project and am having a problem figuring out how to get it it work. It is not so much a circuit problem as a logic problem. Here is what I have (this is obviously not intented as a proper circuit diagram, just a quick hack to show the problem):

B/C/E/F represent subcomponents that I have working fine, H/S/O represent the logical goupings of components that need to be activated together. I am using transistor switches as the physical switches will be replaced by a microcontroller at some point in the future. The problem is (as you might have already seen) that when any of the switches are closed, all the compenents get power. I know I could add some diodes to prevent the backflow (I think it would take 4), but it strikes me that there must be some more elegant way that is completely escaping me.

I would appreciate any ideas, advice, etc. BTW, I am pretty much a beginner, so I apologize of any idiocy in advance. I will be happy to provide any other info or clarification if it would help.

Thanks

#### gumbright

Joined May 22, 2006
4
Oops, I used the wrong transistor symbol on the graphic. Sorry about that. I am using NPNs in the circuit and they work fine (except for the above stated problem, that is).

Joined Jan 10, 2006
614
You'ld do it with 3 diodes. Why arn't diodes elegant..?

#### gumbright

Joined May 22, 2006
4
Originally posted by Gadget@May 23 2006, 01:09 AM
You'ld do it with 3 diodes. Why arn't diodes elegant..?
[post=17289]Quoted post[/post]​
It just seems to me to be a brute force approach. It is patching the problem rather than fixing it. But perhaps that is a completely rational approach in circuit design. That is one reason I wanted to ask others, as this is just my second project. My background is in software development where I have found that a brute force approach is often not the right answer, so that colors my judgement.

I take it you mean the diodes would need to be on EO, SF, & FO?

Guy

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

Isolation diodes are perfectly reasonable to use when trying to use separate input lines. DTL logic would never have functioned without them.

Joined Jan 10, 2006
614
Actually, 4 diodes... sorry, you were right the first time...

#### thingmaker3

Joined May 16, 2005
5,083
A diode is the very soul of elegance. No active component is more basic. The long history of the diode adds dignity.

Brute force is the purview of relays, contactors, and switches.

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