Automatic commit. Wed Aug 8 15:00:03 WST 2012

[matches/honours.git] / thesis / thesis.tex

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@@ -372,6 +372,27 @@ I really think I should actually find plasmonic effects before writing too much
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+\section*{Appendix A - Electron Gun Control and Current Measurement Circuit}
+
+
+\section*{Appendix B - Data Aquisition}
+
+\subsection*{Overview}
+In order to automate recording of TCS data, a data aquisition box (DAQ) was designed and constructed.
+
+\subsection*{Microprocessor and Software}
+The Atmel AVR Butterfly has been used as the 
+
+\subsection*{Power Supplies}
+
+\subsection*{ADC Inputs}
+The AVR Butterfly offers easy access to four of the ATMega169's ADCs through PORTF. Each ADC is capable of measuring voltages (relative to ground) of $0 < V_{in} < V_{cc}$ with 10 Bit resolution. A voltage divider constructed using a variable resistor and fixed resistor allows manual adjustment of the maximum voltage at the ATMega169 ADC input. Diodes between the ATMega169 ADC input, and $V_{cc}$ and ground, ensure that the ADC is protected from exposure to voltages outside the acceptable range. Figure \ref{fig_ADC_normal} shows the typical input circuit, used for three of the four available ADCs.
+
+For differential or ``off-ground'' voltage measurements, the fourth ADC input is passed through an instrumentation amplifier. Low pass filters on the input are used to reduce AC noise on the inputs. The buffer amplifiers ensure that negligable current flows through the measurement circuit to ground.
+Figure \ref{fig_ADC5} shows the input circuit for off-ground voltage measurements. It is important to note that the circuit only functions when the input voltages are within the op-amp common-mode voltage range ($\pm15V$).
+
+
+
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