Demonstration of schemabloc, a set of convenient macros for drawing block diagrams. Documentation is only available in French, but the code examples are easy to follow.

Edit and compile if you like:
% Author: Robert Papanicola
% Source: http://www.sciences-indus-cpge.apinc.org/Schema-blocs-avec-PGF-TIKZ-sous
\documentclass{article}
\usepackage{schemabloc}
\usetikzlibrary{circuits}
\begin{document}
\begin{tikzpicture}
\sbEntree{E}
\sbComp{a}{E}
\sbBloc{b}{$H_1$}{a}
\sbRelier[$E_1$]{E}{a}
\sbBlocL{c}{$H_2$}{b}
\sbRelier[$\epsilon$]{a}{b}
\sbComph{d}{c}
\sbRelier[u]{c}{d}
\sbBlocL{e}{$H_3$}{d}
\sbBlocL{f}{$H_4$}{e}
\sbSortie[5]{S1}{f}
\sbRelier{f}{S1}
\sbNomLien[0.8]{S1}{$S_1$}
\sbDecaleNoeudy[-4]{f}{u}
\sbDecaleNoeudy{e}{v}
\sbBlocr{r1}{$R_1$}{u}
\sbBlocr{r2}{$R_2$}{v}
\sbBlocrL{r3}{$R_3$}{r2}
\sbRelieryx{f-S1}{r1}
\sbRelierxy[n1]{r1}{d}
\sbRelieryx{e-f}{r2}
\sbRelierxy[n2]{r3}{a}
\end{tikzpicture}
\end{document}
Click to download: schemabloc.tex • schemabloc.pdf
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