Bescor MP-101 Hack

I spent a day or two hacking a Bescor MP-101 Motorized Pan / Tilt head to respond to messages from a computer via usb / arduino. Here is the first day in a series of photos. Captions and titles contain some how-to infos. I also took some notes as I was working. They are re-produced,
unedited, below:

Hotbox

Computer Controlled Motorized PanTilt Head

1. Wire Schem

Purple - slowest end of speed control (left)
Yellow - Move Left
Blue - Move Down
Black - Movement common grnd
     note: rx here - gold grey red white grey orange
                         389 x 10^2
                         3.89k ohms[?]
                        
                         actual: 3.78k ohms
         
White - Move Up
Green - Move Right
Red - highest end of speed control (right)

2. power output of pan tilt is roughly 1v (1.005 it seems) to engage servo movement. Measured at DC

3. Arduino code whcih seems to work

     /*
      Fading
 
      This example shows how to fade an LED using the analogWrite() function.
 
      The circuit:
      * LED attached from digital pin 9 to ground.
 
      Created 1 Nov 2008
      By David A. Mellis
      Modified 17 June 2009
      By Tom Igoe
 
      http://arduino.cc/en/Tutorial/Fading
 
      This example code is in the public domain.
 
      */


     int ledPin = 9;    // LED connected to digital pin 9

     void setup()  {
       // nothing happens in setup
     }

     void loop()  {
       // fade in from min to max in increments of 5 points:
       for(int fadeValue = 0 ; fadeValue <= 55; fadeValue +=5) {
         // sets the value (range from 0 to 255):
         analogWrite(ledPin, fadeValue);        
         // wait for 30 milliseconds to see the dimming effect   
         delay(30);                           
       }

       // fade out from max to min in increments of 5 points:
       for(int fadeValue = 55 ; fadeValue >= 0; fadeValue -=5) {
         // sets the value (range from 0 to 255):
         analogWrite(ledPin, fadeValue);        
         // wait for 30 milliseconds to see the dimming effect   
         delay(30);                           
       }
     }

4.      255 pwm output == 5v == broken pantilt head.
     seems 55 fade value is about right, providing a max output of about 1.006v
    
6. Aruino code which outputs correct voltage for controlling the pantilt head


     int ledPin = 9;    // LED connected to digital pin 9
     int fadeValue = 51;    // pwm output for triggering "button pushes" for the pantilt head

     void setup()  {
       // nothing happens in setup
     }

     void loop()  {

         analogWrite(ledPin, fadeValue);        
 
     }