\section{Data Aquisition Hardware}
-{\bf NOTE:} This is slightly out of date, since when the 610B ammeter mysteriously broke, I just used ADC5 for everything. So I can probably leave out all the stuff about the differences between ADC5 and the other ADC's.
-
\subsection{Overview}
+During this project, more than 6000 total current spectra were recorded. This would not have been possible without automation.
+
In order to automate TCS experiments, both Digital to Analogue and Analogue to Digital Convertors were required (DAC and ADC). To provide these, a custom DAC/ADC Box was designed and constructed. The box can be controlled by any conventional computer with available RS-232 serial communication (COM) ports. Most modern computers no longer feature COM ports; a commercially available convertor can be used to interface between the box's RS-232 output and a standard Universal Serial Bus (USB) port.
\label{adc5.pdf}
\end{center}
-asdfa
The instrumentation amplifier consists of two stages of operational amplifiers (op-amps); input buffers, and a difference amplifier.
The difference amplifier can be shown using the ideal op-amp model to produce an output voltage proportional to the difference between its inputs:
The low pass filters were added to the inputs of ADC5 after it was found that an unacceptable level of AC noise was being output by the electrometer. The level of noise was too high to be filtered in software, for reasons that will be discussed in Appendix D.
-\subsection{Temperature Measurement}
-
-The AVR Butterfly features an onboard thermistor connected to ADC0. Reading ADC0 and applying the formula given in the AVR Butterfly User's Guide \cite{} results in a temperature measurement. This was useful in establishing a link between the changing chamber pressure and the temperature of the laboratory (see Appendix C).
-
\subsection{Power Supplies}
Due to the presence of both analogue and digital electronics in the DAC/ADC box, three seperate supply voltages were required:
\begin{enumerate}
The buffer amplifier ensures that negligable current can flow from the power supply into the logic and ADC circuits, whilst the capacitor removes high frequency fluctuations of the power supply relative to ground.
\subsection{DAC Output}
-A commercial DAC board was used to produce the DAC output. The Microchip MCP4922 ET-Mini DAC is controlled by the AVR Butterfly using Motorola's Serial Peripheral Interface (SPI) Bus. The software used to implement SPI between the MCP4922 and the AVR Butterfly is discussed in Appendix D.
+A commercial DAC board was used to produce the DAC output. The Microchip MCP4922 ET-Mini DAC is controlled by the AVR Butterfly using Motorola's Serial Peripheral Interface (SPI) Bus.
The ET-Mini DAC can only be powered off $3V$ to $5V$. Using $V_{cc} = 3.3V$ means that the DAC output cannot exceed $V_{cc} = 3.3V$. For TCS, energies of up to $15eV$ are required, so amplification of the DAC output was clearly necessary. A simple non-inverting amplifier with a manually adjustable gain was used to amplify the DAC output by a factor of three. This output was then used to control a laboratory power supply to produce the full range of initial energies.
Although the RS-232 is relatively simple to implement, which makes it ideal for non-proprietry microprocessor applications, most modern computers no longer feature RS-232 COM ports. Although a computer with COM ports was available at CAMSP, due to the extreme unreliability of this computer, it was quickly replaced with a laptop that did not possess COM ports, and a commercial RS-232 to USB converter was used to interface with the laptop.
+\subsection{Software}
+
+The data aquistion system required software to be written for both the AVR Butterfly and the attached processing computer. The AVR Butterfly software has been written in C, and is based upon open source examples provided by Atmel. The interface for the attached computer was written in python.
+
+We will not include any detailed description of the software here. More information is available on request.
+
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