From 730a583d8a66ff5e4103696ac1977db7b20282b1 Mon Sep 17 00:00:00 2001
From: Blaise Thompson <blaise@untzag.com>
Date: Tue, 13 Nov 2018 19:01:47 -0600
Subject: 2018-11-13 19:01

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+\documentclass{manual}
+
+\title{Dual Low-Current Galvanostat}
+\author{Blaise J Thompson}
+
+\begin{document}
+
+\maketitle
+
+% TODO: photo of final product
+
+\section{Overview \& Performance}
+
+The dual galvanostat is designed to force a small, constant current through an electrolytic cell.
+The voltage floats to whatever is needed to maintain that current.
+The maximum rated output voltage is 13 V, although in practice the voltage may be able to float several hundred millivolts above 13.
+The positive output (red) is guaranteed to be greater than or equal to the negative return (black), in voltage.
+Each output of the dual galvanostat is independent, such that the applied voltages may be different.
+However, the current set-point of both outputs is the same.
+
+The dual galvanostat is designed to deliver relatively small currents accurately.
+These small current set-points can be crucial when driving particularly slow reactions.
+When a galvanostat is set to a current that the reaction of interest cannot support, the galvanostat will naturally swing the output voltage higher.
+Often, the galvanostat will end up driving higher-potential undesirable reactions that are more kinetically favorable.
+For this reason, this galvanostat has been designed to hold current set-points between 10 $\mu$A and 9.99 mA.
+
+\autoref{fig:setpoint} shows the agreement between the set current and actual measured current for a constant load of 100 $\Omega$.
+Note that the data is displayed on a log-log plot.
+The output and setpoint agree to within measurement error for all setpoints above 0.30 mA.
+Below this setting, however, the agreement worsens---the measured current consistently overshoots the set current.
+The absolute deviation between setpoint and measured current never exceeds 30 $\mu$A.
+Please note that the galvanostat is still capable of maintaining these low currents.
+The displayed value simply may not correspond to the actual current, so an independent calibration is warranted.
+
+\clearpage
+\begin{figure}
+  \includegraphics[width=\linewidth]{../data/2018-11-13/setpoint}
+  \caption{
+    Measured current versus set current.
+    On this log-log plot, the entire set-point range of 10 $\mu$A to 9.99 mA can clearly be seen.
+    For both outputs, agreement within measurement error is achieved from 0.30 mA to 9.99 mA.
+    Unfortunately, both outputs become nonlinear at the lowest setpoints, systematically overshooting the desired current.
+    For an unknown reason, the agreement is worse for the left-hand output.
+    All readings were taken with a load of 100 $\Omega$.
+  }
+  \label{fig:setpoint}
+\end{figure}
+\clearpage
+
+\section{Troubleshooting \& Repair}
+
+\section{Appendix}
+
+This appendix contains the following:
+\begin{itemize}
+  \item parts list
+  \item circuit schematic
+  \item full board
+  \item top layer
+  \item bottom layer
+\end{itemize}
+
+\clearpage
+\subsection{Parts}
+
+\begin{table}[h]
+\begin{tabular}{ l | l | l | l | l }
+  name & part & vendor & cost (USD) & comment \\ \hline
+  enclosure & Bud XXX & & XXX & \\
+  power recepticle & & & & \\
+  fuse & & & & \\
+  switch & & & & \\
+  panel-mount pot & & & & \\
+  2x BNC panel mount & & & & \\ \hline
+  power supply & & & & \\
+  standoffs & & & & \\ \hline
+  U1 & LM7905 & UW Stock & 2.00 & TO-220 package \\
+  U2 & TI LM311 & \href{https://www.digikey.com/product-detail/en/texas-instruments/LM311N-NOPB/LM311NNS-NOPB-ND/6175}{Digi-Key} & 1.00 & \\
+  U3 & TI SN74121N & Digi-Key & & \\
+  U4 & TLV4110IP & & & \\
+  U5 & INA105KP & & & \\ \hline
+  R1 & & & \\
+  R2 & & & \\
+  R3 & & & \\ \hline
+  C1, C2, C3 & 10 $\mu$F electrolytic & UW Stock & 0.25 & must be rated over 15 V\\
+  C4 & 10 nF ceramic & UW Stock & 0.25 & \\ \hline
+  J1 & Molex 22-23-2031 & UW Stock & 0.25 & 3 pins, 2.54 mm pitch \\
+  J2, J3, J4 & Molex 22-23-2021 & UW Stock & 0.25 & 2 pins, 2.54 mm pitch \\
+\end{tabular}
+\end{table}
+
+Parts list.
+Costs are approximate.
+Trivial components like screws are not included.
+
+\includepdf[landscape=true]{../PCB/schematic.pdf}
+\includepdf{../PCB/pcb.pdf}
+\includepdf{../PCB/front.pdf}
+\includepdf{../PCB/back.pdf}
+
+\end{document}
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