Simple Block Diagram (TikZ)

It's the first time for me using the TikZ package. I wanted to build such a block diagram but it is becoming really hard. The diagram below was made with Word and it looks pretty inaccurate. Could anyone help me? • Have you ever used TikZ before? See for example this question and this question. – Karlo Apr 27 '16 at 12:15
• Also. could you elaborate on what you want to change about this? Accuracy in terms of what? – sheß Apr 27 '16 at 12:20
• welcome! start small, and build up :) start by creating one node with some text, then another, then connect them, then build from there. lots of people could answer this, but it will be more valuable for you if you try something yourself and then let us know which bit is giving you trouble – cmhughes Apr 27 '16 at 12:26

Just start at one end and work your way through

\documentclass[a4paper]{memoir}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
% I tend to like placing nodes manually
\begin{scope}[minimum width=15mm,minimum height=10mm]
\node[draw] (v1) at (0,0) {$v_1$};
\node[draw] (v2) at ($(v1)+(6,0)$) {$v_2$};
\node[draw] (v3) at ($(v1)!0.5!(v2)+(0,-2)$) {$v_3$};
\node[draw] (v32) at ($(v1)+(0,-4)$) {$v_3$};
\node[draw] (v33) at ($(v32)+(0,-12mm)$) {$v_3$};
\node[draw] (v34) at ($(v33)+(0,-12mm)$) {$v_3$};
\node[draw] (v35) at ($(v34)+(0,-12mm)$) {$v_3$};
\node[draw] (v36) at ($(v35)+(0,-12mm)$) {$v_3$};
%
\node[draw] (v37) at ($(v36)+(-4,2)$) {$v_3$};
\node[draw] (v38) at ($(v37)+(0,-12mm)$) {$v_3$};
\node[draw] (v39) at ($(v38)+(0,-12mm)$) {$v_3$};
\node[draw] (v40) at ($(v39)+(0,-12mm)$) {$v_3$};
\end{scope}
% arrows
\draw[->] (v1) -- (v2);
\draw[->] (v3) -- (v3 |- v2);
\foreach \n in {32,33,34,35} {
\draw (v\n) -| (v2);
}
\draw[->] (v36) -| (v2);
%
\foreach \n in {37,38,39,40} {
\draw (v36.west) -- (v\n.east);
}
\end{tikzpicture}

\end{document} • @Zarko it's my default class in Emacs so shows up automatically ;-) – daleif Apr 27 '16 at 14:48
• memoir It is my favorite document class, but images (alone) I usually draw in standalone :-) – Zarko Apr 27 '16 at 15:00
• @Zarko I've started using standalone, but often it is just as fast to do what I normally do: screen grab + cut in gimp – daleif Apr 27 '16 at 15:03

And one more with TikZ ... style inspired by Bernard answer, node positions are determined relatively by power of tikz library chains.

\documentclass[tikz,border=3mm]{standalone}

\begin{document}
\begin{tikzpicture}[
node distance = 3mm and 21 mm,
start chain = A going below,
every node/.style = {draw, rounded corners, fill=white,
minimum width=12mm, minimum height=6mm,
on chain=A}
]
% main column
\node                       {$v_1$};            % A-1
\node[below=12mm of A-1]    {$v_2$};            % A-2
\foreach \i in {1,2,...,4}% since all have the same content
\node                       {$v_3$};            % A-3 ... A-6
% left subcolumn
\node[left=of $(A-4)!0.5!(A-5)$]    {$v_3$};    % A-7
\foreach \i in {1,2,3}% since all have the same content
\node                       {$v_3$};            % A-8
% right node
\node[right=of A-1]         {$v_2$};            % A-11
% arrows top
\draw[->] (A-1) -- node[below=6mm] {$v_3$} (A-11);
\draw[->] (A-12) -- (A-1 -| A-12);
% arrows right
\foreach \i in {2,3,...,5}
\draw (A-\i) -- (A-\i -| A-11);
% last arrow right
\draw[->] (A-6) -| (A-11);
% last arrow left
\foreach \i in {7,8,...,10}
\draw (A-\i.east) -- (A-6.west);
\end{tikzpicture}
\end{document}

The comments in code is intended to easy find what parts of code doing. For better understanding it is recommendable to read TikZ manual, part 3 (TikZ ist kein Zaichenprogram). One can do something nicer than Word with pstricks:

\documentclass[12pt, a4paper, x11names]{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}    %

\newcommand\Vframe{\myframe{#1}{$V_3$}}

\begin{document}

\begin{pspicture}
\psset{linearc=0.05, framearc=0.25, framesep=0.3, shadowcolor=SteelBlue4!60, shadowangle=-90, arrowinset=0.15, emnode=p}%
%%% nodes
\begin{psmatrix}[rowsep=0.25, colsep=1.6,mnode = r]%
& \myframe{V1}{$V_1$} & \pnode{J} & \myframe{V2}{$V_2$} \\[3ex]
& &  \Vframe{V3} \\[3ex]
& \Vframe{V32} \\
& \Vframe{V42} \\
\Vframe{V51}   & \Vframe{V52} \\
\Vframe{V61}   & \Vframe{V62} \\
\Vframe{V71}   & \Vframe{V72} \\
\Vframe{V81}
\end{psmatrix}
%%% arrows
\ncline[arrows=->]{V1:Cr}{V2:Cl}
\ncline[arrows=->]{V3:tC}{J}
\ncline{V51:br}{V72:Cl}
\ncline{V61:br}{V72:Cl}
\ncline[arrows=->]{V71:Cr}{V72:Cl}
\ncline{V81:tr}{V72:Cl}
\psset{angleB=-90, nodesepB=3pt, linearc=0.1}
\ncangle{V32:Cr}{V2:bC}
\ncangle{V42:Cr}{V2:bC}
\ncangle{V52:Cr}{V2:bC}
\ncangle{V62:Cr}{V2:bC}
\ncangle[arrows=->]{V72:Cr}{V2:bC}
\end{pspicture}

\end{document} 