Problem with circuitikz, subfig and current directions

Question

I've been searching for hours and I can't find a hint about what did go wrong, except that nobody ever tried to do what I intend (?).

I need to include several circuits (via circuitikz) in a document using the tufte-book template, inside the same figure (I don't need the references, just some captions inside the subfloat).

Here is what I intend to do:

\documentclass[justified]{tufte-handout}

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

\usepackage[main=spanish,english]{babel}
\usepackage[caption=false]{subfig}

\usepackage{tikz}
\usepackage{tikz-3dplot}
\usetikzlibrary{shadings}
\usetikzlibrary{babel}

\usepackage{circuitikz}
\ctikzset{bipoles/length=.8cm}
\ctikzset{label/align=straight}

\usepackage[group-separator={.},output-decimal-marker={,}]{siunitx}

\begin{document}
\begin{figure}
  \subfloat[][]{
    \begin{circuitikz}[scale=.8]
      \draw (0,0) to [battery1,l=\SI{6}{\volt}] (2,0);
      % This line works:
      %\draw (0,0) to [R,l=\SI{2}{\ohm},i=$I_1$] (0,2);
      % This doesn't, and it's the one I need working:
      \draw (0,0) to [R,l=\SI{2}{\ohm},i<=$I_1$] (0,2);
      \draw (0,2) to [short] (2,2);
      \draw (2,2) to [R,l=\SI{2}{\ohm},i=$I_2$] (2,0);

      \draw (2,0) to [short] (4,0) to [R,l_=\SI{4}{\ohm},i=$I_3$]
      (4,2) to [battery1,l_=\SI{8}{\volt}] (2,2);
    \end{circuitikz}
  }
\end{figure}
\end{document}

The problem is that with I_1, I need the specific direction, so I need to include the < inside i<=$I_1$, but that bracket is what causes the problem (if I remove it, everything goes smoothly). I know that arrowheads conflict with Babel, so I included the tikz library required to fix that, but even removing Babel, the issue arrises.

My option is to manually create a label inside the figure for each subfigure, but I don't know how to properly align it or the best method for that, and I've read that subcaption doesn't work with Tufte books yet.

I use the latest TeXLive full installation on a Debian Testing (Stretch).

Thanks!

Answer 1

I wasn't sure which way you wanted your arrows to point, so I made them all point up.

As for subfigures and compatibility with babel, the easiest solution is to create your own. Babel defines \figurename and \listfigurename, but you really don't need a subfigure name. The only compatibility issue would be if the alphabet changes.

\documentclass[justified]{tufte-handout}

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

\usepackage[main=spanish,english]{babel}

\usepackage{tikz}
\usepackage{tikz-3dplot}
\usetikzlibrary{shadings}
\usetikzlibrary{babel}

\usepackage{circuitikz}
\ctikzset{bipoles/length=.8cm}
\ctikzset{label/align=straight}

\usepackage[group-separator={.},output-decimal-marker={,}]{siunitx}

\newcounter{subfig}[figure]

\newcommand{\subcaption}[1]% #1 = text
{\bgroup
  \stepcounter{subfig}%
  \sbox0{\textbf{(\Alph{subfig})}\ #1}%
  \par\vskip\abovecaptionskip
  \ifdim\wd0<\linewidth \makebox[\linewidth]{\box0}%
  \else\sbox0{\textbf{(\Alph{subfig})}\ }%
    \usebox0\parbox[t]{\dimexpr\linewidth-\wd0}{#1}%
  \fi
  \par\vskip\belowcaptionskip
\egroup}

\begin{document}
\begin{figure}
  \begin{minipage}[b]{0.5\textwidth}
    \centering
    \begin{circuitikz}[scale=.8]
      \draw (0,0) to [battery1,l=\SI{6}{\volt}] (2,0);
      % This line works:
      %\draw (0,0) to [R,l=\SI{2}{\ohm},i=$I_1$] (0,2);
      % This doesn't, and it's the one I need working:
      \draw (0,0) to [R,l=\SI{2}{\ohm},i=$I_1$] (0,2);
      \draw (0,2) to [short] (2,2);
      \draw (2,0) to [R,l_=\SI{2}{\ohm},i=$I_2$] (2,2);

      \draw (2,0) to [short] (4,0) to [R,l_=\SI{4}{\ohm},i=$I_3$]
      (4,2) to [battery1,l_=\SI{8}{\volt}] (2,2);
    \end{circuitikz}
    \subcaption{test}
  \end{minipage}
\end{figure}
\end{document}