How to make an H-bridge

An H-bridge is a type of circuit that you can use to get a reversible DC motor to spin both clockwise and counterclockwise.

In other words, this circuit allows you to quickly reverse the direction a motor is spinning by using a switch or controller chip to change its direction.

I'm going to show you how to make the simplest and most reliable form of H-bridge that I know how to make. I must warn you that this is by no means the best H-bridge design and, in fact, it has a couple shortcoming which I will explain later.

Although, should you never have made an H-bridge before or simply need a circuit that can reverse the direction of a motor's spin, then this circuit is a quick and easy solution.

(You will notice the motor freaks out when I flip the switch. That is the motor changing directions!)

This H-Bridge was made with the love and support of Eyebeam

Step 1 Go get stuff.

Here's what you need to get:

4 - SPST 5VDC Reed Relays (Radioshack Model: 275-232 Catalog #: 275-232)
1 - SPDT 5VDC Reed Relay (Radioshack Model: 275-240 Catalog #: 275-240)
1 - package of 9V battery clips (Radioshack Model: 270-324 Catalog #: 270-324)
1 - 9V battery
1 - Toggle or slide switch (SPST)
1 - 7805 Voltage Regulator (Radioshack Model: 7805 Catalog #: 276-1770)
1 - PC Board (Radioshack Model: 276-150 Catalog #: 276-150)
1 - reversible DC motor

(You can find a reversible DC motor inside a broken Walkman or Discman. For those of you in NYC, you can get a motor and/or broken Walkman at Argo Electronics - 393 Canal Street)

Comments

[Robot Lover]

If you have a DPDT relay, the other relays are non-essential for making a motor reverser circuit.

[ARJOON]

the relay is so expensive

[laxhead94]

do you really need a 7805 in there?

[milsorgen]

I was just at Radio Shack and the relays alone for this project are going to set you back over 20 dollars.

[Nu]

The relays are being counted from right to left. The fist relay is the one farthest to the right, the second is the next one to the left and so-on. Thanks Nu

[thecookiemonster]

you know you could just use a dpdt switch!!!!

[colin55]

Simply flick the switch to reverse the motor and it creates a brake function.

[ijabi]

Hello colin:do you have any simple way to do h-bridge with mosfet(a Schematics by chance). thanks

[colin55]

There are lots of circuits on the web using MOSFETS in an H-bridge arrangement. These are generally high power circuits and you need to do your own research as there are so many designs.

[Patented]

There should be a simpler way to do an H-bridge than this one

[elginsteve]

There is, a lot cheaper version too using four bi-polar transistors instead of relays.

[amando96]

can i just use transistors, and is the voltage regulator really that important? coz i cant get one :(

[dagenius]

I dought that the 7805 is mportant. if you really feel the need to not burn out your motors, then order a few off of digi-key.

[amando96]

used continuous rotation servos, easier to work with lol

[dagenius]

agree.

[Noodle93]

Or an IC.

[awkrin]

there is a way of doing thing with a more complicated switch that's actually made by two separate switches and changes from one to another terminal, like a SPDT, but it's double: DPDT I mean:

[dagenius]

colin55 has the same circuit.

[Hydrotec]

I want to as a ? Can anyone help me ? I want a automatic timing switch that will change polarity back and forth as well do PWM on and of to speed a motor and slow a motor!

[dagenius]

use a 555 timer circuit, and maybe use one of those fancy digital potentiometers to change the speed. Another 555 circuit would also help for that, if you don't want to use a digi-pot. just make the circuit have a very short cycle, and by changeing that, you may also more reliably change the speed of the motor.

[thermoelectric]

Try this ask ewilhelm if that circuit doesn't suit u

[colin55]

There is a much-simpler way to reverse the motor using just one relay. Connect a double-pole double-throw relay as shown in the enclosed diagram. No other components are required! Just a switch to energise the relay for forward or de-energise the relay for reverse. Colin - TALKINGELECTRONICS.COM

[Deviantgeek]

colin55: then you would not be able to brake

[dagenius]

just add another switch from one of the wires that goes to the motor, and then no matter which way you turn the first switch, the motor will only spin if you have the second switch on.

[godfreyandthandi]

if you really need braking you can tie in a relay somewhere else to cut power.

[rip333]

use a center off DPDT

[raykholo]

really cool idea -- definitely gonna try this couple of questions though -- total cost? can this be done with dpdt relays so u wont have to use as many? cost of an actual h bridge circuit and anything important on those? thanks rak

[colin55]

Of course you can make the project with a double-pole double-throw switch and not use any relays at all. The only problem is the motor is constantly turning in one direction or the other. The alternative is to use two double-pole push switches or 4 switches as shown in the following diagram. You need to push both of the forward switches at the same time. By pushing the reverse switches very briefly you will get braking when travelling in the forward direction.

[cl0ney]

you rock. thank you for teaching for free.

[PyroMonger]

I made a MUCH simpler H bridge by sumply using 2 AA batteries a SPDT switch and Voila! Of course i used a motor too or there would be no point of making it. I found it right here on instructables too. The BeetleBot

[awkrin]

I know that's like that: but that uses only one battery, while a DPDT it's even simpler and uses both batteries

[Artificial Intelligence]

Hey awkrin.
I've posted a little instructable with it here.

[Artificial Intelligence]

Nice, but if you just wanna control the motors direction with a switch, there is a much simpler and easier alternative.

[EvilSnoopy24]

when I had to make one, I gutted a nes controller, and used it to control a little car. but I used the up arrow for one switch and the down arrow for the other switch. anyways here's the diagram

[wi-fi astronomer]

I did the same thing but with only 2 SPDT relays and a bipolar power supply. What you do is hook the motor to the common end of the relay's arm and the normally ON ends to one side of the supply. The normally OFF ends of the relays are hooked to the other side of the supply. When you activate ONE relay, the motor turns. Activate only the other, the motor reverses. Activate both, and the motor remains off. When I made this, you'll never imagine the use I made for it. I used the H-Bridge to control an old cordless drill with threaded rod chucked into it to open and close a window. A window with a remote!

[randofo]

You should post an Instructable of that window openeer. That sounds awesome.

[wi-fi astronomer]

Yeah, that was a cool invention. Until I made it I never heard of a "window servo". It did have a few problems, the most notable was that the whole assembly would vibrate severely so you'd want to let go of the button every few seconds when using it. It sure worked, but you had to know how to use it.

[TerraPlop]

Elegantly complex solution to a simple problem that can be solved with half the parts and at less cost.

[chavez00001]

true

[supafupa]

An H bridge gives you more control. You can interface with a microcontroller, using software to control the speed/direction. With a switch, the intelligence is left up to the operator.