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do you think this would work if i wired it up to a picaxe 14M

ok this is a circuit i have come up with to try and not use a motor driver for my picaxe,

i will have the base transistors connected to pins of a picaxe 

i will appreciate your input 

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If you are willing/can order parts, is there any reason you would be apposed to simply using a motor driver chip? L293D for example, is sorta the "standard" and would run that motor just fine.

Oh, and again, closer... You show in your schematic using 8 pins to control the hbridge and ask about 2 transistors on one pin. --Yes, this is the way it is done. The connections would be "diagonal", one pin controls 2 transistors. --Check out the schematic that Dannyv posted above.

I can't read your writing and a few things are missing. Skip it for now, doesn't matter.

Ok, here we go:

I assume you did some looking around and found a schematic for a simple h-bridge. From there, it seems you have copied part of it and mixed it around a bit. Understand, I am not trying to make fun of you here, but for the life of me, I can't figure on how you got to where you are now. If I sorta knew the steps you took to get where you are now, I might be able to steer you a bit better.

I guess I will start you with this:

This is what it is supposed to look like. Note the resistors on the bases of the transistors and the diodes. Also note that this is for one motor and allows forward and reverse. You will need (2) of these set-ups for (2) motors but neither one will share any pins with the other (except for power and ground).

From here you just need to ask questions. "Is this right?" is not going to work much more --the more specific the question, the more specific the answers.

For a few days i am wondering how to do this. I don't understand why in practice this resistance is so important ? Stupid me !

They say it is pulling up my current, but which one - those of the parallel port's pin i am using or thou of transistor ?

Isn't the current on Gate triggering the flow ?

"Lets say" i have a motor rated at 30V, consuming 4 Amps of DC .

So the next thing to ask is - 4A is normal, but how much should i need to turn opossite with full load ?

- This answer i suppose should answer for the transistor's rating (- 20)% probably.

Next : as i understand  in the diagram that transistor's ratings have no matter(If they are below supply) and 1KOhm is good enough when using power supply in range between (2.2 to 9,6)V.But what about 30V, or 48V with 20A ?

And about Ω again 

Other place i see the formula R = 5 / {[(Vcc / Rc) / B] * 4 } , where B is the gain of Transistor, Rc should be at my motor, and 5 are the volts on Gate. 


So please, Somebody help ! I need to find a way to calculate it i want to make this motor spin.

1. I don't think you'll get a reply here, except for me, telling you to start another post.

2. Gates are for FETs. Bases are for BJTs.

3. There is a lot going on in your post. Try to single out a specific topic and use it as your post subject. It will get better views than the vague "Please help" title.

Let's get that motor spinning.


Thank you, Jack ! You are a nice man ! 

Tomorrow i will take advantage from your advice.



You said, "i understand  in the diagram that transistor's ratings have no matter(If they are below supply)". This is not correct. transistor ratings are very important. I look forward to you starting your own post / thread, so I may explain further.


In case you are not sure how to make your own post, just go over to the right ------->>

and scroll to the bottom of the list. Near the bottom you will see the "Quick links" group. There is an entry, "Create content".

If you click on that you should get a new page with entries such as,

Blog entry  Create blog-entries and link it to a robot-project.. Or just tell us anything you want to share :)
Challenge  A challenge/competition/something.
Component  What are your robots made of? Help others by describing a component we do not already have in our list of components.
Forum topic  Create a new topic for discussion in the forums.
Robot project  Are you working on a robot, or have you finished one? Enter it here.
Something Else  A place for other projects, thingies that are not robots or components or blogs.
Tip/walkthrough  Did you just learn something? Or have you gained expertise in something? Share it with the rest of us, by adding a tip, guide or a walkthrough.

If you are working on a robot, click: "Robot project".

If you are building something else, then click: "Something Else".

If you are not building anything yet, but want to ask a question, you can also use: "Blog entry".


Hope that helps.

Right I have:


2n3904 NPN transistors about 100 of them

I don’t have any PNP transistors as of yet have you got any to recommend me?


For motors I was thinking of getting these






I haven’t used diodes much I would need a bit of help on them


And thank you for the H bridge circuit


I have used the one you showed me and used my wonderful skills on paint to draw this, I recon I have probably missed something obvious   







so i would be able to operate two transistors on one pin would that be acceptable? 


As to PNPs the 2N3906 is the PNP compliment to the NPN 2N3904, ---But any PNPs that have good enough specs will work.

You asked, "so i would be able to operate two transistors on one pin would that be acceptable? "  Yes, that will work as long as you follow the rest of the instructions.

In fact to avoid Q1 and Q2 being on at the same time (or Q3 and Q4, also) and shorting out your power, their inputs can be tied together. BUT, you should reverse their places -that is, do not have the collectors together. The emitters should be together. This is for reasons of positive switching without shorting the power supply. Since one transistor is a PNP and one transistor is an NPN, they will be on at different times.  Here is a sketch I drew for someone else that will give you the idea.

With the emitters tied together, as pin 1 (or pin 2) raises in voltage, Q2 (or Q4) are forced into an off state BEFORE Q1 (or Q3) turn on.  If you have them wired the way your H-bridge drawing shows, you have the real possibility of shorting out your battery/power supply. Q1 and Q2 will both be on at the same time when the voltage is floating anywhere between full on and full off, and Q3 and Q4 will also both be on at the same time. This would be safe if there were current limiting resistors, but a big no-no on a direct coupled circuit.  Your drawing will test the transistors for maximum smoke and test your batteries to see if they will still recharge after having a dead short on them. Oh, and if the batteries do hold up for a few seconds, it may also test your wires to see how much current it takes to melt them.   :-)

Hope that helps.

Dan M.

No. This will not work.

You are sorta close to making an H-bridge set-up. I would start there --searching for "H bridge" or "H bridge schematic".

will this work now ?