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 ;) 




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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I hate to resurrect the dead thread but......

 This is sort of just what I'm looking for! I need a design that will only switch current. I noticed that changes had to be made through the comments. Would someone be really nice and post a schematic I can use that will power a 24V, 5A system? I have no idea what components would be needed for that type of power..I've started a search.

I also plan on using a D flip flop to make the bridge switch back and forth.



Check out these h-bridges.


Hey - I actually wrote to Chuck recently, and even got a reply! Fun thing is that I wrote because I wanted to make sure he never deleted that tutorial, as it was getting old.

Chuck told me that he was hosting it himself now, and that it was going nowhere!

But I have a copy just in case :D 

/ Frits

I wrote up a tutorial as well on how to build a simple transistor H-Bridge. You can find it here:




I will never forget your tutorial Chuck. I think it was the very first thing I read when I investigated how H-bridges worked and it was extremely helpful. Thanks for the awesome work and I encourage everyone who wants to drive their motors themselves to read it!

Hope to see more tutorials from you in the future!

- Jimmy

Chuck commenting on my blog?

Man, you are a LEGEND! OF course I already entered a link to your famous H-bridge tutorial!!

It is right here: http://letsmakerobots.com/node/121

- We must get a better overview on that links-section in here!

But of course, that is the best!

Reason for the original blog-entry on this long thread was that I just wanted the head on Yellow Drum Machine to be able to turn both ways. Just that simple task; flip voltage. And I found that just hooking up an L293D Motor driver was the simplest though overkill IMHO. I´d hoped for some smart wiring with a couple of transistors, but no, this was the fastest.


Anyway, again, I am honored that you actually is in here :) I hope that you will post something?


/ Frits

David Cook has written a nice and short introduction to H-bridges using bipolar junction transistors here


- Jimmy

I am not getting anything of this, so I can only say this rather off-topic:

Hey JIP, you can get 9V as rechargables, at the same price as one new Duracell (10USD in Denmark, Harald Nyborg)

/ Frits 

Thanks for the tip! I just read the description from the batteries you pointed me to... "High capacity which makes them suitable for devices with high current demands"... I don't think any 9V can deliver high current :-). Since both the charger and the battery are so cheap (the charger is about 15 USD) - and since I live really close to that store - I definitely think I will go get some!

The alkaline ones that I have now I bought from www.batterier.dk and I think it was 12 batteries for 250 DKK (which is about 50 USD).

- Jimmy

I have now tested the h-bridge design (where the NPN are connected correctly) and it seems to work. I used LEDs instead of a motor: green is one direction and red is the other. I guess it's not so easy to see what the heck is on the breadboard but the camera couldn't go any closer without blurring the whole thing up... The resistors used in series with the base-pins are 2.2K


And the other direction:


Please note that the green LED in the middle is just the power indicator connected to the voltage regulator (an 7805 in this case). Also you can see my picaxe setup on the right side of the breadboard with my homemade programming circuit for use in a breadboard - nice and handy!

- Jimmy