I am using NPN transistors in an H-bridge to connect a DC motor to ground. My problem is the base of the transistor seems to be grounding through the emitter pulling the value of my logic circuit to zero. This causes the logic circuit to jump to another phase.
Edit: It is setup almost identical to this.
Except there is a separate signal to each transistor coming from the logic circuit. I have PNPs on top (Tip42) connected to the voltage source and NPNs on the bottom (Tip120) connected to ground.