Prop Activity Board servo control - Problem, Diagnoses, Solution

John Kauffman

Here is an entry in the literature in case another person is searching forum for same problem

As a learning exercise I'm trying a servo control with pulse_out() instead of servo.h
The output looks good on the PropScope but nothing on servo.

Code below.

H'ware:
Prop Actiity Board
Servo sockets jumper set to 5 (not Vin)
Power from USB
Servo into left-most socket 12 - white wire at top.
Tested with 2 servos
Scope connected to pin12 socket on left (straight to chip, not servo header) and black to GND

Symptom:
Servo does not move, chatter or resist external force.
When I turn on power to servos (position 2) I get a blip of movement.
Almost seems like no power to servo.

Scope shot attached:
Measurement of pulse width (between vert cursors) = 1.8 mSec
Measurement of high to high (pulse interval) = 22 mSec
Signal matches expected output and conforms to servo specs

Diagnosis:
Since there seemed to be no power I thought along those lines.
Voltage should be OK:
Servo needs at least 5v to operate
USB power is 5 v
Socket jumper set to 5v
BUT: current.
I switched power from USB to a wall wart into power jack and problem solved.

TAKE HOME:
Working with servo on PAB? Must use external power, not USB.