cant drive my h-bridge

[ahmedragia21]

hi , i've two PWM pins from PIC16F877 , the problem is im using L298 and i already have 10 PCBs and the enable pin is tied to 5V , i dont know how to pwm the h-bridge then at the same time i want to reverse and forward the motors forward and backward ....

is there a simple soultion to achive that ?
thanks

 

[Nigel Goodwin]

You already know, use the enable pin! - if you've made the PCB's wrong then get a sharp knife around it!.

 

[ahmedragia21]

cant i drive the PWM pin to the IN1 ( input 1 ) ? and use a transistor to cancel that line when i want to use the input 1 as it is ?
hope u understood me ?

 

[Nigel Goodwin]

cant i drive the PWM pin to the IN1 ( input 1 ) ? and use a transistor to cancel that line when i want to use the input 1 as it is ?
hope u understood me ?

There are plenty of things you can do, but all of them far more complicated than using the enable pin - for example you can use a handful of logic gates to steer the PWM to the correct pins. Cut the PCB and run a wire!.

 

[ahmedragia21]

ok , i will try to cut the pcb
what's a good PWM Frequency for a line follower robot to move smooth ?
1khz ?

 

[Nigel Goodwin]

ok , i will try to cut the pcb
what's a good PWM Frequency for a line follower robot to move smooth ?
1khz ?

That would be fine, you don't want to go too high, but 1Khz to 4KHz should be no problem.

If you want sample PIC code for PWMing a robot, check my 'tutorial' - it gives basic two channel speed control code for just what you want.