Thanks for the suggestions. I had to put this away for a while, but I'm back for the weekend.
The problem is in the setup, not in the loop. The twitch is at the myservo.attatch() and myservo.write() commands. As AWOL suggested, I tried swapping those commands and also adding a delay(1000) in between the commands. None of these ideas worked. What's shown below is the last code I tried.
#include <Servo.h>
Servo myservo;
int servo = 9; // pin output to control the servo
int start = 50; // start position of servo
int finish = 130; // finish position of servo
void setup() {
myservo.write(start); // move servo to start position
myservo.attach(servo); // attaches the servo to pin 9
*** non-servo related code removed ***
}
void loop() {
*** all this code works fine ***
}
oric_dan - (a) I've tried 3 servos, and they all do this. I'm buying cheap servos, so maybe that's the problem. (b) In my system, the servo will always end in the start position for the next operation. I don't have to worry about this part of the initial servo jump.
EDIT - corrected comments in code to pin 9