The IceCube Digital Optical Module (DOM) main board (MB) is a single board data acquisition computer primarily designed to timestamp and record the arrival of photons produced by subatomic particles loosing energy near photomultiplier tubes in the ice. The IceCube Optical Module (OM), a 13" Dia. sphere, constitutes a platform for other research by virtue of the MB's auxiliary input interfaces. For the digital inclinometer, JP14, a socket near the board's configuration memory,
provides a sufficient number of pins for inclinometer control and readout. Minor revisions to the Field Programmable Gate Array (FPGA) code and software running on the DOM MB allow for the inclinometer module to be controlled and read out.
An "ADIS16209 Demo Board" from Analog Devices has been mated to a DOM MB using point-to-point wiring in order to confirm both electronics functionality and inclinometer performance. The test dictated that a custom FPGA code be developed (a minor modification of the production FPGA firmware design), and data read from the inclinometer. Test data is available for review and analysis. Results are summarized in the proposal.
The goal for the project is to have inclinometers deployed into IceCube in the Dec-'09/Jan-'10 season.
Visit the Schematic, Top, and Bottom printed circuit board layers for a look at the technology. The printed circuit board measures ~1.25" x 1.25" with an over-all height < 3/8" above the DOM MB when installed (the spacing between the DOM MB and flasher board is 1.25".
Since only pin friction will hold the inclinometer board, it is prudent to use a material like RTV to restrain the inclinometer board in place above the configuration memory. A "spot" of RTV (roughly 1 gram) between the configuration memory and the inclinometer will suffice to anchor the inclinometer board in place. A single component RTV will adhere well to the PCB solder mask and to the plastic configuration memory package. RTV also behaves well at low temperature; it doesn't get brittle and fracture; after curing it is inert.
Another version of this layout was created which has the 20 pin connector shifted significantly to the left to insure that the edge of the board would not extend over an arced cut-out of the DOM main board central cut-out. Unfortuantely, a mistake occurred during procurement that resulted in an earlier layout version being produced. Fortunately, when the board was actually mounted on a DOM main board, and the board placed over the plastic PMT neck cover shroud, no fatal interference was observed. See pictures at the end of the gallery.