Hi, I am building an H Bridge to drive a 2A @ 12V motor and I am using a 555 timer for the signal, so I tested the circuit at 7.5V DC but the motor only rotates in one direction, I use a 4.7k variable resistor for controlling the motor and this only makes the motor speed slow when the variable is turned fully anti-clockwise n the speed fast wen the variable is turned fully clockwise. Any suggestions on how I can change the direction.

 

You need an inverter for the second pair of transistors to switch on for reverse like this circuit
http://www.google.co.uk/imgres?q=h+...w=197&start=0&ndsp=15&ved=1t:429,r:5,s:0,i:87

it uses a second 555 as an inverter, but you could use an ordinary npn transistor and two 10k resistors.

 

Thnx Dave bt now the circuit needs to have an OFF state and dts when the variable resistor is in mid position, I'm suspecting the variable coz I first used a small one and the motor only vibrated then I only got motion when I used the 4.7k...oh one other thing is when I played around with variable resistor dat is moving it from side to side, the motor wud change direction.

 

You talk weird. Text speak? DTS is a company isn't it?
Please type in complete English words so you do not read like a little kid.

 

dts- that's
Coz- because
Dt- that
Wen- when
bt- but
Wud- would

Hope u understand now, please appl these to the post above and not forgetting the suggestion please.

 

Thnx Dave bt now the circuit needs to have an OFF state and dts when the variable resistor is in mid position, I'm suspecting the variable coz I first used a small one and the motor only vibrated then I only got motion when I used the 4.7k...oh one other thing is when I played around with variable resistor dat is moving it from side to side, the motor wud change direction.

I dont get what your on about, please can you post your schematic ?