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Description:

This is my second prototype of automated Barn Door Star Tracker. The first one made of wood and screw was a total failure due to the imprecision while aligning the motor to the shaft and due to the weight.

Goals:

1-Automated.
2-Cost below 20$ in part.
3-Run on batteries

That created some constraint on the possible solutions. I had to reduce the size of the motor, so use quite a lot of gear to achieve the desired torque and low speed required. Lego Technic were perfect for this application.

Hardware part:

1x Microchip controller DSPic30f2010. (With minimum parts, no crystal and no power filtering.)
1x DC Motor 5v 20RPM (GA12-N20)
1x L293D Push-Pull Four-Channel Motor Driver IC
1x Optical Encoder Correlation photoelectric sensor

For an example of the used hardware, please watch: https://www.youtube.com/watch?v=1PTPRkB5JZo

Source code:

Under files you will find the source code to be compiled with MPLAB IDE. The code is written in C.

InitializeTimer1() Sets the timer given the gear ratio of the setup.
InitializeIO() Sets the Inputs and Outputs

Usage:

A button allows to change modes between: Stop, Sync Forward, Fast Forward, Sync Reward and Fast Reward.
An optional LED show the actual mode.