Let's Make Robots!

H-Bridge Troubles

I was able to remove the chip from the RC car receiver board, but I didn't have the dexterity and soldering skills to solder leads into the tiny board to use the ready made h-bridge.  My next step was to try and build my own h-bridge, but that isn't working out very well.

I tried to follow this design for an h-bridge.  First, I built the whole circuit and tested it out.  The motor didn't even hiccup.  Next, I tried testing one section at a time.  I started out with the PNP.  I am using a 2n4403.  Here is the Multisim schematic with simulation results for PNP circuit as well as a picture of the actual circuit on my breadboard.

PNP Schematic with Simulation Results

Real PNP Circuit

Once again, the motor didn't move.  After pulling my hair out for a while and reading my electronics textbook I gave it a rest and moved onto the NPN.  I am using a 2n2222a.  Here is the Multisim schematic with simulation results for NPN circuit as well as a picture of the actual circuit on my breadboard.

NPN Schematic with Simulation Results

Real NPN Circuit

The single NPN transistor circuit worked great.  The motor was running like it was connected straight to the power source.  So, I decided to use only NPN transistors and see if that would work.  I made half the bridge to test it out.  Again, here is simulation and real.

NPN Double Switch Schematic with Simulation Results

NPN Double Switch Real Circuit

The NPN double switch didn't work.  I know I am doing something wrong.  I just don't know what it is.  I ordered this h-bridge in case I can't figure this out and also because it seems that it would take up much less space compared to the components I would be using to make my own.  I also have my eye on the kit that OddBot mentioned.  If anyone has some advice I would really appreciate it.

EDIT 9/22/2012: Well I got the half bridge to work using the design mentioned in the beggining.  Expanding to a full h-bridge now to see how that works.

EDIT 9/22/2012 again:  Yeah, the whole problem was my BJT's.  Some of them are broken.  Full h-bridge according to the design mentioned above is working now.  Next step, obstacle detection.

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it looks like you constructed your half h-bridge wrong. The 754410 and the L293 are similar ICs. They are both quad half h-bridge chips. A half h-bridge is the vertical part of the robotroom circuit you used originally. What you finally tried using is jus the top/bottom half of the h-bridge from robotroom. Realize, a half h-bridge will only turn a motor on and off. You will get no bi-directional control from said circuit.

Well, although the final goal is to get a working full h-bridge, right now I am trying to get my half h-bridge to work.  When I tried using a single PNP as a switch it didn't work.  Any idea as to why this might be happening?

I was only able to get the NPN to work as a switch and that's why I tried to use only NPN transistors for the half h-bridge, but that didn't work either.

EDIT: My PNP was broken.  I must have burnt it out with the testing.  I felt it get really hot at one point.  Continuing my testing now.

EDIT 2: I got the half bridge to work....all this from a faulty BJT.  I should really make sure my components are working when every possible resource online says that the design should work.