The philosophy of compactness and flexibility, seen in the design of the computer controlled bias electronics, carries into the software design as well. The I2C signals needed by the electronics is generated at the parallel port of an otherwise normal rack-mounted PC running the Linux operating system. The excellent documentation of system internals, tight use of system resources, remote accessibility via X-Windows, and free compilers and programming tools make Linux an excellent choice for this design. An Intelligent Instrumentation PCI-20428W multi-purpose Data Acquisition (DAQ) card is used for non-I2C control of the instrument. Hardware Independence The actual array software is highly modular and the source code, written in C and supplemented by Perl CGI is nearly independent of the hardware. What does this mean? We have written a separate kernel module (driver) for the DAQ card, so the array controller software is nearly blind to the actual card being used. We can switch from our Intelligent Instrumentation card to a National Instruments LPM-16 card (for which we have also written drivers), and the source code is scarcely touched! Parameters are not hard-coded into the software -- configuration is done by a human readable text file. This means that, for example, you can pull out one SIS card, put another in without paying attention to the card's DIP switches, and no code needs to be recompiled. User Interface The actual graphical user interface takes advantage of the open source, popular and highly capable GTK+ X-Windows toolkit. The design of the interface is compact, gives the user full control of the instrument, and yet is clean and uncluttered. The interface often adopts a "notebook" motif, where each mixer or subsection is a different tab in the notebook. This presents the observer with the information [s]he needs to see, without being overwhelmed with controls that are not necessary at the time. "Stoplight" icons provide immediate "at a glance" information on the general health of the instrument. Remote Access Owing to the isolated nature of submillimeter observatories, especially AST/RO, remote access to the status of the instrument, and even remote control of the instrument, is an extremely powerful and useful tool. The software may be remotely operated from any computer with SSH (Secure SHell, for encryption), X-Windows, and permission. Additionally, the control software spawns a Perl CGI script every 60 seconds (user-definable) which synthesizes a continually-updated web page on the receiver status and performance. Nearly all information presented by the control software is also monitored in the Web page. In this way, anyone with a web browser can assess the state of Pole Star. All of these features are handled easily by a rather slow computer by modern standards. The current Pole Star PC is powered by a 75 MHz AMD K5 processor, comparable to a 75 MHz Pentium, and with "only" 32 MB of RAM. Figure 24: The second serial port on the PC is hooked up to the Lakeshore temperature sensor controller and is monitorable by the software. This is an example of the Pole Star software looking at the cool down curves for Desert Star. Click on thumbnail for full-size image!

Figure 19: Sweeping the #3 mixer in Pole Star. The red curve is the I-V curve, the blue curve represents the total power. Click on the thumbnail for a full-size image! Figure 20: This is a total power sweep, made by pressing the HOT LOAD button. Click on thumbnail for full-size image! Figure 21: This is a second total power sweep, made by pressing the COLD LOAD button. When both hot and cold sweeps are present, the receiver temperature is automatically calculated as a function of bias voltage. This makes it easy to find the optimal bias voltage. In this case, the LO is not powered up; so the hot load (red) and cold load (blue) curves are coincident, and the receiver temperature is undefined. Click on thumbnail for full-size image! Figure 22: This is an array after all, so here is an I-V and total power curve produced by mixer 1 (no LO power). Click on thumbnail for full-size image! Figure 23: We can monitor over 60 signals on the Low Noise Amplifiers. Although the LNA's are usually "set and forget", the "LNA Status" tab allows you to evaluate the health of the LNA's. Click on thumbnail for full-size image!