# Simple Bi-directional Switch

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## Introduction: Simple Bi-directional Switch

Have you ever needed a simple way to control the direction that a DC motor rotates at the flick of a switch? Ever been daunted by complicated circuitry or don't have the equipment to make PCB's? Well you've come to the right place! Today you will learn how to make a super simple switch that will control the direction that a DC motor rotates.

Many small electronics projects can contain a small hobby motor and it is sometimes important to control the direction that it rotates. There are a few options out there such as h-bridges that involve using diodes and transistors to swap the polarity that is applied to the motor however they are far to complicated and require a lot more parts than the simple switch.

For this project you will need minimal electronics skills and only a few basic parts / tools which if your an electronics hobbyist like me, you probably allready have lying around.

Check out the project video above!

So let's get started...

## Step 1: Gather Parts

For this project you will need a few simple parts that you will either allready have lying around or will find at your local electronics store.

To make the switch you will need:

• 1x DPDT switch (double pole double throw). Get one with centre-off if you want forward-stop-reverse control or a normal one for just forward-reverse control.
• Wire

To try the switch out you will need:

• A DC hobby motor
• A power supply (or batteries and a battery holder)

You will also need a few tools:

• Soldering Iron and Solder
• Wire Cutters
• Third Hand Soldering Tool (optional)

## Step 2: Wire the Switch

To enable the switch to be able to swap around the polarity that is sent to the motor it must be wired in a particular way.

First cut 4x 30 cm lengths of wire and 2x 5cm lengths of wire.

Hold the switch so that you are looking at the bottom where the contacts are so that there are 2 columns of 3 pins

Next solder two long lengths of wire on each of the the bottom two legs that are next to each other and the other two longer lengths of wire on the middle pair of legs.

After that, solder the 2 short lengths of wire in a cross shape between the top two and the bottom two legs on the switch.

This step is much easier to follow using the diagram that I have included above.

And that's it! Let's test it out!

## Step 3: Connect to the Motor

To connect the switch to the motor and try out our creation use the following steps:

First connect the two long wires from the bottom two legs to the power supply of your choice. Polarity doesn't matter.

Secondly, connect the other two long wires that come from the middle two legs to the motor. Again polarity doesn't matter.

Check out the diagram above if you become confused.

## Step 4: Results, Troubleshooting and Extras.

Results

When the switch is put in one position, the motor spins forwards and then goes backwards when put in the other position. Also, if you used a centre-off switch, you will be able to get the motor to stop when put in the centre position which depending on your application can be quite useful.

Troubleshooting

Q. The motor doesn't spin at all when I provide power to the switch. What can I do?

A. First of all check that all your connections are secure and complete either by eye or using the continuity function on a multimeter and also check for short circuits. If there is still a fault, check that the type of switch you are using is DPDT and not DPST. After all this, check that it is not a problem with the power supply by taking a voltage reading if possible. If all else fails, there is likely a fault with one of the components of the circuit so check every component individually to rule out any faulty or damaged parts.

Q. The motor spins in the wrong direction to what I want it to. How can I fix this?

A. This is a rather easy fix. Either swap the two wires around that connect to the motor or swap the two wires around that connect to the power supply.

Extras

An idea to take this project further could be to use a DPDT relay so you will be able to control the direction of the motor electronically so that it can be incorporated into other outputs of your project. The idea is the same, the only difference would be putting power to the coil to control the direction of rotation.

## Recommendations

• ### Large Motors Class

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• ### Space Challenge

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## Questions

This even works with AC motors. BTW the switch is still a single throw, but just with a center off position. Which is actually the official name for the switch, it is a double pole center off switch. Sometimes called an ON-OFF-ON switch too. The center off does not count as a throw, because it is no connection. It is basically a busted DPST switch, that hangs in the middle.

6 replies

Controlling an AC motor to do a similar thing is a little more difficult as there is no polarity as such to swap around, hence alternating.

Back to DC, it is not actually necessary to have a centre-off switch, a normal DPDT will do the job fine, it just depends on your application whether centre-off is required.

Hope that helps!

I would suggest staying with center off switches when wiring this way. Not all switches are "break before make" meaning you could potentially have a dead short momentarily when throwing it. The center off gives you some dead space for safety.

I've wired motors up with just the DPST switches. But then I need a separate power switch too. I've only ever done induction motors that way, and trying to change their rotation while they're running is pointless, nothing happens. As the start winding is disconnected while the motor is running. Once the motor is running you can flip that switch and it does nothing at all. Because there's no power to it. The centrifugal switch is open then.

Actually I've done it many times. AC does in fact have a polarity too. At least common wall current in the US does. One leg is neutral, which is ground. But that is besides the point. AC motors work on repulsion though, so if you change the phase of the coils in relation to each other you change the direction of the magnetic fields. What that means in the context of this discussion is, if you use this switch on one coil, you change the motor rotation. This works with induction motors, and universal motors run on AC. I've done it with both.

Actually, this IS a DPDT switch. You are correct that it is called an on-off-on switch, if it is center off, but it is not a busted single throw switch. The number of throws refers to how many outputs a single input can connect to. In this case the center input can connect to either the top end, or the bottom end, thus is has two throws. It has two poles because the pins are not connected internally, so each side of three pins is basically a single pole double throw switch.

There are different versions of this switch depending on any the internal connections, including ones that have the crossover shown here wired internally to the switch already. So you have the read the printing on the side of the switch to determine which one you have.

The on-off-on is most common.

Very clear and well explained! It is true that there can be many different types of DPDT switch and as stated by you it is important to identify the correct one. This one in particular is a standard on-off-on DPDT toggle switch.

Thanks for the contribution!

Your Instructable is very well presented! An alternative solution is to purchase a 4-way switch from a hardware store. Many households with three or more wall switches use 4-way switches to control a single light or load . Internally, these switches are wired the same as yours. Only, there is no center OFF position.