Parallel switches, multiple functions

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Larry, I was afraid that if I activated C using the S3 switch, the current would also activate A and B, which I don't want. Is that not right?

I was under the impression that I would need diodes, but I'm not sure how to properly implement them. Everything in the circuit runs on 120V AC. I was under the impression that diodes are typically for handling low voltages...
 
110322-2127 EDT

rickwire1:

Diodes are not just a low voltage device. A diode is something that is a low resistance in one direction, and a high resistance in the opposite direction. A single tube diode was used as the high voltage rectifier in TV sets since the beginning. I haven't looked in a modern TV and therefore I do not know if semiconductor diodes are used today.

Diodes can be used in logic circuits.

In your case the statement of the problem is incomplete.

You want Out1 and Out3 to be on when In1 is asserted.
You want Out2 and Out3 to be on when In2 is asserted.
And you want Out3 to be on when In3 is asserted.

Let's further require that when any one or more Outs are on that the brightness of any Out that is on is the same as any other. This will prevent you from using the series circuit.

Besides this information you need to define what happens to the outputs for any combination of input switches. This makes it much more complex so forget this by saying that no more than one input switch is to be asserted at any time.

You can solve this problem with two DPST switches (double pole single throw), one for input 1 and one for input 2. And a single SPST switch for In3. See if you can draw the circuit.

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gar said:
110322-2127 EDT
You can solve this problem with two DPST switches (double pole single throw), one for input 1 and one for input 2. And a single SPST switch for In3. See if you can draw the circuit.
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Click to expand...

Gar beat me to it by the time I got to answering... I'm interested though in knowing what this "pet project" is about though.
 
Just so I'm not missing anything here the swich arrangemnt will work as it currently is required in the problem except each bulb will only be half its brightness because the source will divide the voltage between the two bulbs in series?
 
How about 2 dp switches, one sp switch and three contactors. S1 turns on A & C, S2 turns on B & C and S3 only needs to be SP , turn on C
 
mull982 said:
Just so I'm not missing anything here the swich arrangemnt will work as it currently is required in the problem except each bulb will only be half its brightness because the source will divide the voltage between the two bulbs in series?
Click to expand...

I don't think the OP mentioned what the load is although many responses assumed a light bulb, which is why I was curious about what the OP is actually trying to accomplish... but yes you will have a voltage divider with two loads in series.
 
They don't look like light bulbs to me. And what exactly does it mean to turn any of them on? If, for example, they are relay coils, perhaps half voltage might cause them to change the state of their contacts, and perhaps not. What I don't get is the purpose of the question. The sketch appears as though it might provide an acceptable answer, so why show us the sketch and then ask the question?
 
I believe that all you need is double pole switches for S1 and S2.

For S1, wire half to A, and half to B. For S2, wire half to B and half to C, and for S3 wire to C.

Wire them so the switches are in parallel. Half of S1 in parallel with S2....

Steve
 
rickwire1 said:
Larry, I was afraid that if I activated C using the S3 switch, the current would also activate A and B, which I don't want. Is that not right?
Click to expand...
No, once S3 is closed, it will basically provide a short circuit path around A and B. So no current will flow through A or B.

Think of it this way: The voltage across a closed switch is zero (since it has zero resistance). With S1 or S2 closed, A or B is in parallel with S3. Since the voltage is always the same arcoss parallel elements, the voltage across A or B would also be 0, therefore they will not be on.
 
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110323-1321 EST

Using the assumptions of my post #10 you can also do the following with diodes:

If the power source is DC, then 4 diodes, and three SPST switches will accomplish the desired result of the same voltage on any energized load.

If the power source is AC, then one additional diode is required for the same voltage criteria. But the load voltage is a half wave rectification of the source voltage.

Again see if you can figure out the circuits, and why the fifth diode is required in the AC case and not in the DC case.

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steve66 said:
I believe that all you need is double pole switches for S1 and S2.

For S1, wire half to A, and half to B. For S2, wire half to B and half to C, and for S3 wire to C.

Wire them so the switches are in parallel. Half of S1 in parallel with S2....

Steve
Click to expand...


That is even easier then what I had proposed-- no contactor necessary. Problem is it would not be legal when two switches were on. The contactors would avoid that.
 
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