Hi, Bernhard.
I really appreciate your detailed reply to my newbie questions.
In your 'buttonPin=2' statement, is the Arduino Uno wiring supposed to already have the button physically installed and also have been pressed by the user in order to work properly?
------- From your instruction ----
Firmware udate: Version 0.4 -> wiring diagram did not match with the firmware. Thank you @andyman2000 for your feedback

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New firmware, Version 0.3, released!
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This is an instruction to build an automated Aruino Turntable
You need:
1) 1 Arduino Uno board
2) 1 10k Resistor
3) 1 10k Potentiometer
4) 1 Push button
6) 1 Servo Motor
7) The printed parts
8) A David-Laserscanner: thingiverse.com/thing:36989
Installation Instructions:
I) Remove the 180° lock from the servo as shown in: feh.osu.edu/Design-Project/References/servo.html
II) Put all parts together as shown in the wiring diagram.
III) Load the firmware (the -ino file) on the board
Operating Instructions:
Open your David-Laserscanner and activate the option: Seetings > Advanced Settings > Communication > COM > Enabled.
This function allows the Arduino board to send commands via the USB connection to the David-Laserscanner.
The turntable has 3 modes:
Mode 0) Nothing happens

Mode 1) If you push the button, the turntable starts to rotate. Now you can adjust the angle of the rotation with the potentionmeter. No scans will be made in this mode.
Mode 2) Once you are satisfied with the rotation angle, push the button again. The table will stop to rotate for 5 seconds. Move away and let the table do its work.
It will rotate, then send a signal to the David scanner. The scanner will make a picutre of the object and save the file. If the scanner is finished, the table makes the next move aso.
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Sorry I do not clearly understand your step-by-step instruction.
I have installed David version 3.7 32bit on my PC running XP.
Thank you for you kind help.
Bryan