Martin Teichmann Atomes de lithium-6 ultra froids dans la ... - TEL

3.8. COMPUTER CONTROL
where the code could not be maintained. We rewrote the whole experimental
sequence, adapting it to the new setup and removing large parts
that had become unnecessary. During this rewrite we optimized the code
interfacing with the bus, cutting in half the time between commands to
5 µs.
The cameras are connected to two different computers, which in turn
are connected via serial ports to the control computer. We preferred to
use two computers as the camera imaging the magnetical and optical
traps is connected to the computer via an old PCi card and we feared
that it would not be compatible with modern computers, while the MOT
camera is connected via USB 2.0 which is not compatible with the old
computer.
The data acquisition program controlling the cameras had become
even more cumbersome. Many different data analysis tools had been
introduced which we were not able to manage. This led to frequent
crashes of the program. When the new MOT camera arrived, it was
nearly impossible to adapt the old program to the camera, so it was
decided to write a new program from scratch. We chose Python as a
programming language, since it has an easy to understand structure and
automatic garbage collection, eliminating memory leaks which we think
was the problem causing the frequent crashes. Our design goal was to
keep the program as simple as possible, making it understandable as
a whole. To achieve this task we used readily available libraries from
the Internet wherever feasible. Namely we used Qt4 and PyQt for the
graphical user interface, matplotlib [92] for plotting the acquired images
and SciPy [93] for fitting our data. We could thus decrease the size of the
program from more than 25000 lines to below 2000 lines. The running
program is shown in figure 3.18. An important problem of the old
program was, that the calculation of the physical values were distributed
over the whole program. After a while they did not correspond to the
actual experiment anymore, but it was cumbersome to change the code
appropriately. The new program contains all physical calculations in
one single file, shown in figure 3.19, which can even be changed during
runtime.
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