Hi,

Several years ago I was trying to figure out a way to allow a motor to
be controlled by a computer interface (to allow it to go both forward
and backward by just applying a voltage on one of two lines). I
designed a device that could (theoretically) do it using transistors.
I later learned what the name of the device I had designed was.

Last night I finally managed to build an H-Bridge. I had previously
tried it, but there were problems (mostly materials wise) that
prevented it.

I made it last night and hooked it up to a DMM to test. I used a 9V
battery as the external power source and gave it a run. It worked
great, the DMM read about -9 when using one lead, and +9 when using the
other. The problem is that it wasn't ±9V but rather ±9mV. The
polarity was correct, but the output was about 1/1000 of the input.
This makes it useless since I don't have a 9,000V power supply to drive
the motor.

I'm guessing that the transistors I used are the problem since the rest
of the device is just wires; that they are somehow also acting as
resistors.


Here's the schematic I made of the H-Bridge I built:
http://img233.imageshack.us/img233/8966/hbridgeua9.gif

I'm using regular wires from various computer parts (the kind that
connect buttons and LEDs on the front panel to the motherboard), and I
got the transistors from the circuit board of a television. They are
marked "C815 Y312" (I checked them with the diode testing function of
my DMM, and they they all tested tested fine-and yes, I've got the
pins correct.)


Like I said, the polarity works, but the output is far too low. Any
ideas on what's going on and how to fix it?

Thanks a lot.