Synchronous 4-Bit counter circuit using JK-flip-flops

The circuitikz package provides macros for typesetting electrical and electronical networks. Here it's used to draw a 4-bit counter circuit. It's a synchronous counter, i.e. the circuit is synchronized by a clock signal. The counter is built using JK-flip-flops. A flip-flop is is a circuit with two stable states, useful for storing state information.

Edit and compile if you like:

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% Synchronous 4-bit counter circuit using JK-flip-flops
% Author: Henri Menke
\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{10pt}%
\usetikzlibrary{calc,arrows}
\usepackage[european]{circuitikz}
\begin{document}
\def\JKFF(#1)#2#3{%
  \begin{scope}[shift={(#1)}]
    \draw (0,0) rectangle (1,1);
    \draw (0.5,1) -- (0.5,0);
    \draw (0.5,0.5) -- (1,0.5);
    \node at (0.75,0.75) {$Q$};
    \node at (0.75,0.25) {$\bar{Q}$};
    \draw (1,0.8) -- +(0.25,0) coordinate (#2 Q);
    \draw (0,0.2) node[right] {$K$} -- +(-0.25,0) coordinate (#2 K);
    \draw (0,0.5) node[right] {$T$} -- +(-0.25,0) coordinate (#2 T);
    \draw (0,0.8) node[right] {$J$} -- +(-0.25,0) coordinate (#2 J);
  \end{scope}
}
\begin{tikzpicture}[every path/.style={},>=triangle 45]
    % Place the JK-Flip-Flops
  \JKFF(0,0){a}{$Q_0$}
  \JKFF(2,0){b}{$Q_1$}
  \JKFF(5.5,0){c}{$Q_2$}
  \JKFF(9,0){d}{$Q_3$}
  % Connect all the K and J ports
  \draw (a K) to[short,-*] (a J);
  \draw (b K) to[short,-*] (b J);
  \draw (c K) to[short,-*] (c J);
  \draw (d K) to[short,-*] (d J);
  % Connect the T ports to the incoming signal
  \draw (-1,-1) node[ocirc,label={left:$E$}] (E) {};
  \draw (a T) -- ++(-0.2,0) coordinate (inter) -|
    (E -| inter) node[circ] {};
  \draw (b T) -- ++(-0.2,0) coordinate (inter) -|
    (E -| inter) node[circ] {};
  \draw (c T) -- ++(-0.2,0) coordinate (inter) -|
 
 
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