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I have a 3-state switch, It has 3 pins. It can have 3 state as you can see in the picture below. when it's off (i.e on O) the middle pin is not connected to anything. When it's on I, the middle pin is connected to I and when it's on II the middle pin is connected to II.

3 state switch

Now, I have one DC motor and a 9 volt battery. I wanted to build a connection between these three elements that when the switch is on O, the motor is off. When it's on I, it turns in one direccion and when it's on II it turns to the other direction. I wanted to avoid using any other logical elements like gates or diodes, etc...

Schematic

All I want to have is just one switch, one DC motor and one DC battery. I've got no idea how to make this happen.

If there is no way of doing it, is there a way to build it with minimum extra required elements?

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  • \$\begingroup\$ You need at least a 2-pole switch to do what you're trying to do. \$\endgroup\$ Jun 7, 2015 at 20:12
  • \$\begingroup\$ Possible duplicate of this question. Dwayne Reid's answer, specifically. \$\endgroup\$ Jun 7, 2015 at 20:38

3 Answers 3

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You can do what you want if you have two batteries.

Connect both batteries in series. Connect both outside terminals of the switch to the outside ends of the batteries.

Finally, connect the motor between the center terminal of the switch and the midpoint of the two batteries.

One battery runs the motor in one direction, the other battery powers the motor in the opposite direction.

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No: You can not. Very simple reason:

The motor's positive can be connected to the middle point of the switch and then you can change if it is connected to the positive or negative of the battery, but since the negative side is connected to only one of the battery terminals, one of those choices if a "brake" setting, shorting the motor, in stead of reverse.

You can fix it with one Single Pole, Dual Throw (SPDT) relay rated for the approximate voltage. Most 12V ones will probably work down to 8V, but there might be a 9V type too.

schematic

simulate this circuit – Schematic created using CircuitLab

If you use the switch to connect the motor's positive to the battery's positive, the relay switches on and connects the motor's negative to the battery's negative and it runs the right direction. If you connect the motor's positive to the battery's negative with the switch, the relay turns off (since it is connected to negative on both sides) and it switches over the Motor's negative back to the battery's positive, forcing the motor to run reverse.

You might want to connect a few diodes here and there for spark protections, but since you want as close to no extra components as possible, this is the minimum. I think a prettier solution would be with MOSTs, but that requires more parts in total.

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It can't be done in a sensible way, you need more contacts, or a split rail supply. There is something called mickey mouse logic, when you use and abuse resistors and diodes to create AND or OR gates without adding another IC.
This would be an example...

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ It works, but drains the battery 5 times faster and continues draining even with the switch off! Also, the motor receives about half voltage so runs slowly. \$\endgroup\$
    – DoxyLover
    Jun 7, 2015 at 20:47

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