2 motor Bi-directional PWM control help

[ashrau]

Hi.

I'm trying to make a 2 wheel self-balancing robot - right in the initial phases.

I am using a PIC microcontroller (PIC18F4220 or PIC18F4620) and a L298N Full H-bridge.

I have learned how to use PWM to control speed of the individual motors - but only in one direction.

Currently, I can controle 1 motor for speed and direction using the 2 PWM pins on the PIC. I would like to control both motors for speed and direction (independantly) using the PWM outputs from the PIC. How can I do this with just 2 PWM pins available on the PIC? Do I need a different PIC with more PWM outputs or is there a way to accomplish this using just 2 PWM outputs?

Any help will be highly appreciated!

Thanks.

ashrau

 

[xainnasir]

Its not a big issue to control motor ..... check the datasheet of L298 ..... for driving one motor you are giving two pins from PIC to L298 ..... if u give 1 0 to these pins then motor will move in one direction and if you give 0 1 it will move in opposite direction ..... if u still have any problem then u may ask ..... but i would suggest to use transistors for motor drive as L298 current rating is not much but if u use FETs u can drive any motor having any load ....

 

[ashrau]

Thanks for the reply! My current circuit diagram is attached.

Here is the issue that I am having with controlling two motors:

I want to control the motor speeds using the PWM function from the PIC. I am using 2 output pins from the PIC to enable/disable the 2 bridges in the L298N. I am doing this by toggling the output b/w HI and LO.

The PIC has only 2 PWM outputs available.

How do I control - through this single PIC - both motors for speed as well as direction? Right now both my PWM outputs from the PIC are tied up with one motor. Do I need a PIC that has more PWM outputs? Or is there a way for me to control both motors through just 2 PWM signals?

The motors that I am using have a peak current (when stalled) of 1.3 A - so the L298N should be O.K to handle the load. I would like to stick to PIC microcontrollers and H-bridges as I am familiar with them.

Thanks again!

Best,
Usman

P.S Some other questions - some explanations on these would be helpful for me as wel:

- Do i need all 4 diodes on each motor? What would be the difference if I used just 2?
- Do I need a seperate capacitor for pin 9 of the L298N?
- Do I need a seperate capacitor for the motors or the current arrangement will be O.K?

 

[xainnasir]

sorry for late replying as I ws bzy ..... First thing u can create PWM signal by urself .... PWM is nothing just a signal with limited 1 .... u can create it with any pin not a big issue and L298 is not so gud I have used it with 12V motor n it gets hot .... if u r using heavy motor then i will suggest u to use transistors or relays .....

 

[ronv]

The PIC has only 2 PWM outputs available.

How do I control - through this single PIC - both motors for speed as well as direction? Right now both my PWM outputs from the PIC are tied up with one motor. Do I need a PIC that has more PWM outputs? Or is there a way for me to control both motors through just 2 PWM signals?

You need some logic in front of the in pin that will send the pwm to the correct side of the bridge. It can be gated with a forward reverse signal from the pic.

- Do i need all 4 diodes on each motor? What would be the difference if I used just 2?

Yes

- Do I need a seperate capacitor for pin 9 of the L298N?

I would add a large cap on pin 9--say 100ufd.

- Do I need a seperate capacitor for the motors or the current arrangement will be O.K?

The schematic shows pin 9 and the motor on the same voltage if they are different I would add the 100 ufd, to the motor supply. If that is the case I would then add just a .1 ufd to pin 9.

 

[Gobbledok]

The PIC has only 2 PWM outputs available.

The only pins on the L298 which need a PWM signal are the 2 Enable pins (EnA & EnB)

You don't need any logic.

Then simply supply In1 and In2 with a '10' for forward and a '01' for reverse (or vice-versa).