# H bridges

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#### Stover

##### New Member
I am planning on using an OOpic as a microprocessor and will be driving 3 ungeared 3vdc motors. I know I can't directly connect the two motors to the OOpic, I'll need an h-bridge. Now, the questions.
1.) What exactly does an h-bridge do?
2.) What one(s) should I use?
3.) How would I set them up?

#### Exo

##### Active Member
An H-Bridge contains all the circuitry you need to make a DC motor run in both directions. in a typical circuit the H-Bridge is connected to the power source. The motor to the H-Bridge and a control signal to the H-Bridge. Now the control signal can make the motor spin left, right or brake.
Some H-Bridges offer a PWM input to let you manipulate the speed of the motor (but you need a external PWM generator for it).

What one you should use depends on what extra features you want it to have, how many power it should be able to handle and so on. Need more info to answer that one.

Actual connection depend on the type of H-bridge used (obviously)

#### Stover

##### New Member
Alright. I want the motors to move forwards and backwards as well as stop. I want to run the three motors on perhaps 6 AA batteries (more or less) so.
I'm not sure if I need a speed control, but it would be useful. What would an external PWM be? I think I can send PWM signals/ recieve them through the oopic.
I understand H-bridges come in chip form and also you can make one but it takes up more space. So now which one is a good one for me to choose?

#### Nigel Goodwin

##### Super Moderator
If you do a web search you will find loads of them, try looking for small robots - a lot of them even use OOpic processors. I even seem to remember that the OOpic website gives examples.

#### Stover

##### New Member
Yeah, but on their site they say that the h-bridge (they picked) controls 10-55 VDC, when I need a much lower one, like 3vdc. I want to know what a good h-bridge would be for that and perhaps a hint on where to put the wires lol

#### crust

##### Member
That is probably the design spec for that particular h-bridge, at your low voltage, I am assuming the motor is rather small. In this case, you can roll your own h-bridge with discrete components. You could for instance use higher Rds_on mosfets (read cheaper) or smaller package parts.

#### ivancho

##### New Member
Since you want IC names here are a bunch that come to mind. I hav use most of them and they work well. Also let me suggest that you could also use a modified servo motor so that te electronics are there already, and you don't need but 1 control line.
All of this chips can handle not that big of a current, so you must kow what your motor's current usage is.Some H-bridges IC are:

:arrow: 754410 Current: 1.1A (2A peak) Price:$3.70-$5
:arrow: L293D Current: 1A (2A peak) Price:$2.00-$5
:arrow: L298P Current: 2A (3A peak) Price:$3.8-$4
:arrow: LMD18200 Current: 3A (6A peak) Price:$11.69-$13.00
:arrow: L6201PS Current: 4A (5A peak) Price:$7.00-$15.00

Most of them have a power rating of 25W only..... so if you only use 3V then you will be able to run at the non-peak current pretty cool... .the higher you go with the voltae the warmer the chip will run and you will need to use a heatsink.

Hope it helps you some,

Ivancho

#### falleafd

##### New Member
Notes that, as using a H brigde chip, you have to download its datasheet to see if it has internal protect diodes or not. If not, you have to build it external. You should use fast diode so that you can use PWM method upto some KHz frequency. If you use 4001 to 4007, you only can drive it upto 20 - 50 Hz.

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