How to improve placement in a series of TiKZ nodes

Question

I am a beginner in LaTeX, and TikZ trying to make an industrial document, with a series of keying patterns. I have managed to produce in the attached MWE what is needed, put I have to adjust manually the position of every half circle into the corresponding hexagon. I wonder if there would be a more sensible way to do this... (ie aligning the center of the half circle with the center of the hexagon). As I have many other configurations to show, where each half circle is to be placed at different angles, I have tried to use a \foreach loop, but could not find a way that would work....I would appreciate any help to improve the code.

\documentclass{standalone} 
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{tikz} % Enabling watermarks and special graphics
\usetikzlibrary{positioning,chains, matrix,shapes,decorations,backgrounds,}
\begin{document}
\begin{tikzpicture}[every node/.style={on grid, regular polygon, regular polygon sides=6,  minimum width=10mm, minimum height=10 mm, draw, very thick, node distance=15mm, anchor= west},]
\begin{scope}
\node[draw= white, rectangle, text width=18em,  ] (0) {\textbf{Coding pattern for plug}};
\node[right of=0, xshift= 4 em,   label=above:1 ] (1) {}; 
\node [right of=0,  xshift= 4 em,   circle, draw, minimum size=7.8mm] {};
\node [right of=0, xshift= 4 em, yshift =1ex, semicircle, fill= black,  minimum size=3.8mm,] {};
\node[right of=1, label=above:2] (2) {}; 
\node [right of=1,  circle, draw, minimum size=7.8mm] {};
\node [right of=1,  semicircle, fill= black, xshift= 0.9ex, yshift= 0.5ex,  minimum size=3.8mm, rotate=-60] {};
\node [right of=1,  circle, draw, minimum size=7.8mm] {};
\node[right of=2, label=above:3] (3) {};
\node [right of=2,  circle, draw, minimum size=7.8mm] {};
\node [right of=2,  semicircle, fill= black, xshift= 0.7ex, yshift =-0.4ex,  minimum size=3.8mm, rotate=-120] {};
\end{scope} 
\begin{scope}[yshift=2cm]
\node[draw= white, rectangle,text width=18em ] (0) {\textbf{Coding pattern for receptacle}};
\node[right of=0, xshift= 4 em,   label=above:4 ] (4) {}; 
\node [right of=0, xshift= 4 em,  yshift=-1ex, semicircle, fill= black,  minimum size=3.8mm, rotate=180] {};
\node [right of=0, xshift= 4 em,  circle, draw, minimum size=7.8mm] {};
\node[right of=4, label=above:3] (3) {}; 
\node [right of=4,  semicircle, fill= black,xshift=-1ex, yshift= -0.5ex, minimum size=3.8mm, rotate=120] {};
\node [right of=4,  circle, draw, minimum size=7.8mm] {};
\node[right of=3, label=above:2] (2) {};
\node [right of=3,  semicircle, fill= black, xshift=-0.7 ex, yshift=0.4ex,minimum size=3.8mm, rotate=60] {};
\node [right of=3,  circle, draw, minimum size=7.8mm] {};
\end{scope}
\end{tikzpicture} 

\end{document}

Answer 1

I have introduced a new command: \plug[<opt>]{<internal name>}{<rotation>}{<label>}

• <opt> may be arbitrary TikZ stuff tat get passed to the circle.
  The hexagon will be positioned in the circle's center, as well as the semicircle.
  (Notice anchor=south! This essentially places the south (the middle of the semicircle's diameter) at (c.center).)
• <internal name> is needed in the positioning of the following plugs.
  But beware, you must use plug<internal name>!
• <rotation>

• <label> places a node above the plug. If you (on a user base) want to have a better ability to place these labels, you may replace

  label={[yshift=1mm]above:#4}
  

  with

  label={#4}
  

  For a one-time override don't use <label> but use the optional argument:

  \plug[…, label={below:5}]{05}{-60}{}
  

Code

\documentclass{standalone} 
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{tikz} % Enabling watermarks and special graphics
\usetikzlibrary{positioning,chains, matrix,shapes,decorations,backgrounds}

\newcommand*\plug[4][]{%
    \node[draw, very thick, circle,          label={[yshift=1mm]above:#4},    minimum size=7.8mm,                                           #1]                    (plug#2) {};
    \node[draw, very thick, regular polygon, anchor=center,                   minimum width=10mm, minimum height=10mm, regular polygon sides=6] at (plug#2.center)          {};
    \node[draw, very thick, semicircle,      anchor=south,        fill=black, minimum size=3.5mm,                                    rotate=#3] at (plug#2.center)          {};
}
\begin{document}
\begin{tikzpicture}[node distance=15mm]
\node[align=left, text width=18em] (text0) {\textbf{Coding pattern for plug}};
\plug[right of=text0,node distance=40mm]{04}{0}{1}
\plug[right of=plug04]{03}{-60}{2}
\plug[right of=plug03]{02}{-120}{3}

\node[above of=text0, node distance=2cm, align=left, text width=18em] (text1) {\textbf{Coding pattern for receptacle}};
\plug[right of=text1, node distance=40mm]{11}{180}{1}
\plug[right of=plug11]{12}{120}{2}
\plug[right of=plug12]{13}{60}{3}
\end{tikzpicture}
\end{document}

Output