servo problem

[shah_siddiquee]

Can anyone tell me why is my servo not workin? I tried on B port pins in my 28x2. I used servo, pulsout and high commands. But still didnot wark. But i tried on port C pins and it worked. I need to mention that, i have axe020 project board and attached darlington ic uln2804 on port B pins. One more thing is i got L293D motor driver. Can i use both darlington ic and motor driver at once?

 

[BeanieBots]

The darlington inverts the signal so it won't work from there.
Either pick up the signal from before the darlington or remove the chip and replace it with either a link or better, a resistor pack of about 330R.

 

[westaust55]

AXE020 PortB pins - Direct Connection points

The newer AXE020 boards (if not also earlier boards) have a row of holes for direct access to the PortB IO pins.
See the attached marked up board photo and schematic from the AXE020 datasheet

 

[westaust55]

One more thing is i got L293D motor driver. Can i use both Darlington ic and motor driver at once?

Again looking at the AXE020 datasheet:http://www.picaxe.com/docs/axe020.pdf
The L293D uses portB pins 4,5,6 and 7.
So while using the L293D to control a motor you cannot also use the same PortB signals through the ULN2803 Darlington chip. You can still use the PortB pins 0,1,2 and 3 through the ULN2803 at the same time as the L293D channels.

 

[shah_siddiquee]

thanks

Thanks guys i got my answer.

 

[shah_siddiquee]

forgot about diod

Sorry i forgot to ask about the diod. Do ineed to use diod for servos as i am not using darlington or motor driver ic. Will Only 330 resistor work? Because the reverse current could damage chip.

 

[westaust55]

Sorry i forgot to ask about the diod. Do ineed to use diod for servos as i am not using darlington or motor driver ic. Will Only 330 resistor work? Because the reverse current could damage chip.

No, a simple 330 Ohm resistor between the PICAXE and Servo signal input will be fine.

 

[rossko57]

No, a simple 330 Ohm resistor between the PICAXE and Servo signal input will be fine.

To explain why, there are control electronics inside the servo, that sit between the Picae signal and the motor itself. They have to deal with any nasty spikes coming from the motor, but they do not let the nastiness back out into the servo control input.

The 330 resistor is a precaution in case the signal line gets plugged into the servo wrong way round or other accident.

 

[shah_siddiquee]

thanks

Got it thanks