Reddit mentions of Humminbird 7700281 GCBK CSB GP1272 Portable AGM Battery and Charger-Color may vary

Quick video that shows it operating, and the basic interface modes (single-button operation):

http://www.youtube.com/watch?v=_mPij7eHOmo

I'm super happy with how well it worked on its very first test, considering how rough the polar alignment was (Polaris went behind my roof when I squatted to sight down the hinge line, so I made a educated guess at where it was). I'm currently living in the LA metro area, so light pollution here is about as bad as it gets, but at least it doesn't impact my ability to do star tests. Can't wait to head out to the desert and see what I can capture.

I posted a few months ago when I just had the mechanical components completed, and it goes into a bit more detail about the design I used [LINK]. The stepper motor is microstep-driven at 16 microsteps per full step, and 200 full steps per rotation of the drive shaft. 1 rotation of the drive shaft moves the camera platform by about 0.25 degrees. Therefore, each microstep rotates the camera platform by about 0.3 arcseconds. Step rate is approximately 50 Hz.

This past week I did all of the electronics:

• figuring out a reliable power supply (big battery)
  
• getting a breadboard setup that can safely deliver power to the motors and logic boards
  
• programming microcontroller to issue timed pulses that drive the stepper motors (via a driver interface board), and handle other minor operations like electronic range limits, pausing, and rewinding
  
  The microcontroller board I'm using is a Sparkfun Arduino Pro Micro (5V, 16 MHz), which is based on the Atmel ATmega 32U4. I chose this for ease of breadboarding and the ability to program over USB.
  
  To calibrate the mount, I used a digital angle measuring cube to record the elevated angle of the mount as a function of turns of the threaded rod driveshaft (logged 138 points with a precision of 0.1 degrees). After deriving the ideal kinematic relationship between driveshaft and mount rotation angle (an arcsin function of driveshaft rotation), I did a curve fit to the data I'd recorded. What I ultimately wanted was a function that would generate a time value for when a pulse should be sent to the stepper motor. This was accomplished by adding in a sidereal tracking rate factor (360 degrees every 23.93 hours, or 7.292 * 10^-5 rad/sec), and accounting for the conversion from microsteps to drive shaft rotation angle.
  
  I then took the trigonometric equation and fit a 3rd-order polynomial to it for quick (~100 µs, much faster than I actually need) evaluation on the MCU, which isn't really made for hefty floating point arithmetic. The polynomial approximation theoretically will accumulate no more than 10 arcseconds of error at any time, so it should be an insignificant factor compared to polar alignment error.
  
  Using a timer on board the microcontroller, an outer loop sequentially calculates the time when each step should be made, while an inner loop waits for that time to arrive before pulsing the motor. The outer loop then calculates the next step time, and the process repeats until the preset step limit is reached. Some additional logic provides the ability to pause and resume tracking from a button input, and also reverse and "rewind" the mount upon request, returning it to its initial state.
  
  Here's a link to the Arduino code it's running:
  https://dl.dropboxusercontent.com/u/31090145/Step_Driver.zip
  
  And a calibration spreadsheet for tuning the mount:
  https://dl.dropboxusercontent.com/u/31090145/step_cal.xlsx