Servo connection

Hi!

In his great book ‘Exploring BeagleBone’, Derek Molloy uses a 1k resistor between the PWM output and the servo pulse input; is it mandatory? Is it a good practice to do that? Do I need such resistor if I use a standard GPIO (soft PWM made by the PRU)?

Thanks.

Frédéric

what page?
usually you need to limit the current otherwise you may destroy the board, though 3mA is usually not enough to drive the servo

what page?

p234...

usually you need to limit the current otherwise you may destroy the
board, though 3mA is usually not enough to drive the servo

Really? It is just a logic signal, not the servo power...

Derek says that the 1k resistor limits the current to 0.01mA.

3.3v/1000ohm(1k) = 3.3mA
3.3/3000ohm(3k) = ~ 1mA

I would put that one in, just in case, to make sure you dont fry the pin by accident
if you have a dedicated part number for the servo, check you the datasheet for the control pin input impedance, its usually in the 10k and you don’t need it; a wild servo i would use it though so as to be cautious.

3.3v/1000ohm(1k) = 3.3mA
3.3/3000ohm(3k) = ~ 1mA

I would put that one in, just in case, to make sure you dont fry the pin
by accident

So Derek resistor is only there to avoid short-circuits, if servo is
malfunctionning...

if you have a dedicated part number for the servo, check you the
datasheet for the control pin input impedance, its usually in the 10k
and you don't need it; a wild servo i would use it though so as to be
cautious.

Ok !

Thanks,

3 mA? AFAIR the maximum that can be pulled out of a (GPIO) pin of BBB is 6 mA…