Just a quick update. Today I implemented the state machine, which was presented in the last log. Now its possible to to switch between manual and auto mode and use the up and down functions.
In a next step the circuit will be moved from the breadboard towards a pcb and mounted into a case. This allows me to do basic tests on the finished hardware.
To ensure portability and to keep the system modular, I choosed to build a external "power box", that will provide the necessary voltages to drive the camera and the barn door. It also can be used without the tracker and will be fed from a 12 volt battery.
The system needs:
3.3 volts, 0.1 (?) amps (atmega)
8.2 volts, 2 amps (camera)
6.8 volts, 1.7 amps (stepper)
which accumulates ( ;-) ) to about 2.8 amps @ 12 v, using 85% effective step down regulators and pretending that the camera and stepper will draw a constant current. Typical lead-acid batteries provide > 7.2 Ah and therefore a running time up to 2.5 hours. In practice this will last longer, as the system won't draw the maximal current over the time.
I think i'll leave some space for a additional 5 volt output, on which i could connect a Raspberry Pi zero. It could controll the camera using pkTriggerCord or PK-Remote and transform the barn door tracker into a standalone piece o technology.
So the next steps are:
Building th pcb and case
Building the barn door hardware
Testing electronics and hardware
Design a cycle-saving way to calculate the step time
Actually I am working on the electronics, which will control the stepper. As the "barn door" parts will be ready this weekend, the electronics should at least be able to drive it for a quick test.
A Finite State Machine will be used to control the whole thing. Two push buttons should allow enough interaction. These states are implemented:
Init (initialisation and homing the barn)
Automatic up (tracking mode)
Automatic down (homing the barn)
Pressing both buttons simultaneously will switch between auto and manual mode. Pressing one of the buttons will either move the barn up or down. Below you find a quick snap of my (really messy) workbench.
As i wrote in my first log, is necessary to turn the upper bar at a constant turn rate.
Let us first take a look at a isosceles triangle. Thinking about a barn door tracker, we could assume, that the two fixed length sides would be about 40 cm long. The variable side (the threaded rod) will be adjustable between 0 cm and 40 cm. The first case of 0 cm gives us an opening angle of 0°. The second case will form a equilateral triangle, which will lead to a opening angle of 60°.
Assuming that the earth rotates at 360° per 1440 minutes, it will take 240 minutes to open the tracker by 60°. Side c (the rod) needs to be extended at 6 minutes per centimeter.
Space - the final frontier. Spending a night under a starry sky offers a fascinating view into the past. To keep those images not only for one night, it's easy to set up an camera and take some photos.
Unfortunately (?) the earth keeps rotating, which makes it hard to get a picture of a star as a point. As shown in the picture below, this can also be a nice effect.