PWM signal from PIC as opposed to PWM signal from function generator

[variaseng]

Hi! I'd like to ask what is the difference between the PWM signal produced from a function generator and a PWM signal produced by a PIC microcontroller. I am trying to produce PWM signals to drive a DC motor. This PWM signal is fed to the motor driver through a octal transceiver 74LS245. But when I try to drive it using the PWM signal from the PIC, it does not move as opposed to when I use the PWM signal from the function generator (PWM signals have the same amplitude, frequency and duty cycle). Thank you very much for your help!

 

[3v0]

I expect the PIC does not provide enough current. The PIC output is generally 25mA. To drive a motor you need to use the PIC signal on the base of a transistor to control a source of power with more current. A 2N2222 will provide about 750mA.
**broken link removed**

 

[variaseng]

Okay, thank you very much. I will try this and update. Another question, when I try to connect the PIC directly to the driver without the transceiver(74LS245), the motor moves okay. It's just when I drive the motor through the 74LS245 that I encounter a problem. Is the current still the problem here if this is the case? Thank you very much for your help!

 

[3v0]

Wow I sort of botched this up.

I read the post then promptly forgot about the 74LS245 and the motor driver.

What is the motor driver ?

How about a schematic showing how you have things connected. Words only go so far.

but: if the motor is not too large all you need to drive it from the pic is a transistor.

 

[xainnasir]

i have worked on such a project recently but my motors are really very heavy .... so i used FETs for motor PWM and they work really great ...

 

[pilko]

@ xainnasir,
It would be helpfull if you would post your schematic and motor specs.

Regards

pilko

 

[xainnasir]

dnt have the schematic rite now and i was using 40 V motors geting around 3-4 A current

 

[ronv]

Your pic may need a pull up resistor on the pin you are using.