Servo control panel in Python and Tkinter with a circular gauge

The problem

After building control forms in VB.NET, the next step was an interface in another language that reads better at a glance: an operator wants to see the current angle, not only read a number.

Solution and data flow

• Interface: a Tkinter window titled Servo Control Interface, with a Scale from 0 to 180, buttons for 0°, 90° and 180°, and a label showing the current angle.
• Circular gauge: a CircularGauge class on a Canvas draws a half-circle arc and a needle, mapping the value to a drawing angle and then to coordinates with cos and sin.
• Sending: the angle goes out as newline-terminated text over pySerial at 9600 baud, and is not sent if it is outside 0 to 180.
• Board: the Arduino sketch reads the number with Serial.parseInt, checks the range again before myServo.write, and replies with an error message when it is out of range.

Implementation and challenges

Checking the range on both ends stops a bad command from driving the servo into its mechanical end stop, even if it comes from another program. The serial port is closed when the window closes so it is not left locked. This was a personal exercise during the degree, on an Arduino board and a small hobby servo.

Skills developed

Tkinter interfaces and custom Canvas widgets, serial communication with pySerial, servo control, and range checking on both ends of a link.