\begin{circuitikz}[scale = 0.5, transform shape]
%  \draw[help lines] (0,0) grid (8,6);
%  \foreach \x in {0,...,10} \draw (\x,-1) node {\x};
%  \foreach \x in {0,...,7} \draw (-1,\x) node {\x};
  

  % uref
  \draw(0,3) to[V_<=\large{16V}, l^=\large{$U_{ref}$}] (0,5);
 
  % Switches
  \draw (4,1) node[spdt,xscale=-1, yscale=1, anchor=in] (z0) {};
  \draw (z0.in) node[anchor=south] {z0};
  %leiterwiderstaende
  \draw (z0.in) to[R=$2\cdot R_0$, a=2$k\Omega$] (6,1)
  to[short] (7,1) to [R=$R_0$, a=1$k\Omega$] (7,3);
  %an potentiale anhaengen 
  \draw (z0.out 1) node[anchor=south west] {\tiny{+16V}};
  \draw (z0.out 2) node[anchor=north west] {\tiny{0V}};
  
  \draw (4,3) node[spdt,xscale=-1, yscale=1, anchor=in] (z1) {};
  \draw (z1.in) node[anchor=south] {z1};
  %leiterwiderstaende
  \draw (z1.in) to[R=$2\cdot R_0$, a=2$k\Omega$] (6,3)
  to[short] (7,3) to [R=$R_0$, a=1$k\Omega$] (7,5);
  %an potentiale anhaengen   
  \draw (z1.out 1) node[anchor=south west] {\tiny{+16V}};
  \draw (z1.out 2) node[anchor=north west] {\tiny{0V}};


  %z2 ist auf 0V geschaltet, => ausgaenge vertauscht
  \draw (4,5) node[spdt,xscale=-1, yscale=-1, anchor=in] (z2) {};
  \draw (z2.in) node[anchor=south] {z2};
  % leiterwiderstaende
  \draw (z2.in) to[R=$2\cdot R_0$, a=2$k\Omega$] (6,5)
  to[short] (7,5) to [R=$R_0$, a=1$k\Omega$] (7,7);
  %an potentiale anhaengen   
  \draw (z2.out 2) node[anchor=south west] {\tiny{+16V}};
  \draw (z2.out 1) node[anchor=north west] {\tiny{0V}};

  
  \draw (4,7) node[spdt,xscale=-1, yscale=1, anchor=in] (z3) {};
  \draw (z3.in) node[anchor=south] {z3};
  %leiterwiderstaende und oberster sprossenwiderstand
  \draw (z3.in) to[R=$2\cdot R_0$, a=2$k\Omega$] (6,7)
  to[short] (7,7) to[short] (7,9) to[short] (6,9)
  to [R, l_=$2\cdot R_0$, a^=2$k\Omega$] (4,9)
  to [short](2.5,9) to [short] (2.5,6.5);
  % an potentiale anhaengen 
  \draw (z3.out 1) node[anchor=south west] {\tiny{+16V}};
  \draw (z3.out 2) node[anchor=north west] {\tiny{0V}};

  
  %alle schalterausgaenge nr. 1 verbinden
  \draw (z0.out 1) -| (1.5,2);
  \draw (z1.out 1) -| (1.5,2);
  \draw (z2.out 1) -| (1.5,2);
  \draw (z3.out 1) -| (1.5,2);
  % mit u_ref verbinden
  \draw (z3.out 1) -| (0,5);

  
  %alle schalterausgaenge nr. 2 verbinden
  \draw (z0.out 2) -| (2.5,2);
  \draw (z1.out 2) -| (2.5,2);
  \draw (z2.out 2) -| (2.5,2);
  \draw (z3.out 2) -| (2.5,2);
  % mit 0V verbinden
  \draw (z0.out 2) -| (0,3);
  % ground-ref anhaengen
  \draw (2.5,0) node[rground]{} to [short,-*] (2.5,0.68);

  % ausgang
  \draw(7,1) to[short,-o] (8,1){};
  \draw(8.5,0.5) node[]{\Large{$U_a$}};
  \draw[-{Triangle[scale=2.5, length=2, width=2]}](8,0.8) -- (8,0.2);
%  \draw(8,-0.2) to[short,->] (8,-0.8);
  \draw (8,0) to[short,o-] (8,-0.2) node[rground]{};
  
\end{circuitikz}
