Let's Make Robots!

The darn H-bridge

I just want to be able to reverse a current. How hard can it be?

I just want to be able to decide direction of the motor to my pic, why does it have to be so complicated?

Well - perhjaps it doesnt! Jip / Jimmy, the most clever guy in here just drew me this and send it to me.P2290333.jpg

The smallest and most-likely-to-burn-something H-bridge in the world!

If it works, I will make a full walkthrough about it.

If it burns my robot.. well.. he did warn me ;) 

 


Notes:

 

Transistors are seen from top (usually you see them drawn from below) 

 


Motor will turn one way when

 

A = low, B = low, C = high, D = high

Other way when A = high, B = high, C = low, D = low

 

Motor will halt if A = high, B = high, C = high, D = high

 

... shortcut and smoke if A = low og B = high or C = low and D = high

 

 

 

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Frits I did warn you about not putting the darn thing online before you tested if it worked :-). I'm no electronics wizard so things that I conjure up are bound to be broken from the start :-D

A little note on the above H-bridge: it is not recommended for use by others than Frits who apparently wants to burn his transistors and chips :-). I think the design is correct but I didn't really test it :-D. At the very least there should be some schottky diodes for transistor protection and capacitors on the motor for spike protection (I think that's how it works anyway).

Fredrik you're quite right in that MOSFETs should be used instead of BJTs and if you really want a good and effective H-bridge you should use only N-channel MOSFETs since these have a lower internal resistance than P-channel (this does impose some requirements on your supply voltages though). Looks like a nice tutorial you found but the design it shows doesn't allow for electronic braking.

It would be nice to see some different motor controller designs. I was thinking of building something which works kind of like L293 with having a voltage for the motor and still being able to control it from TTL voltage levels directly from the picaxe. I think maybe this can be done by using an op-amp to drive each transistor (and you can get four op-amps in one chip with the LM339)... I should make a drawing so you guys can see and tell me if it is crap and not working :-).

- Jimmy

Yes, there is a 1.5V voltage drop within the L293D, and yes, it can only take so much of a load.. But it is simple, and it works.

I am going to make a L293D walkthrough for dummies - I have so far only used it in the picaxe 28 project board.. But it is actually very nice as a quick stand alone-fix!

More later,

/ Frits 

There is also an L298 chip that can handle more current and can sense the motor voltage (this can be used for telling how fast the motor is running - I think :-))

 - Jimmy

No rotation, nothing, does not work, something is wrong.

Will try to just use a L293D

Hate this shite!

 

Thanks, Fredrik, but I am too stupid for this, and I just want to make robots, hate electronics, am too stupid ;/

/ Frits

You could contruct it so that you only need 2 inputs. Also, if you do that it would be preferable to use MOSFET transistors instead as they work for both directions. If you use an combination between NPN and PNP transistors you'll have to use a total of 6 transistors.

Societyofrobots has a really good tutorial that covers H-bridges though it only covers it with MOSFET transistors: http://www.societyofrobots.com/schematics_h-bridgedes.shtml