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Using Python and 19,200 bits/second serial links to manage antennae for the Square Kilometre Array radio telescope in Australia

Friday 11:40 AM–12:10 PM in Hall A

Part of the Our Connected Universe specialist track

The Australian half of the Square Kilometre Array radio telescope will collect 7.2 Terabits/second of raw data from 131,072 antennae grouped into 512 'stations' with 256 antennae each - but every antenna needs to be connected to a box within a few metres of that antenna, for a DC power supply, and to convert the electrical output to light over optical fibre before it degrades. This talk will describe those boxes, and how they are being monitored and controlled using Python, a 40+ year old communications protocol, and a network of 19,200 bits/second serial links.

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The Australian part of the Square Kilometre Array telescope will have 512 stations in the Murchison region of WA, each a circle of steel mesh on the ground with 256 two-metre tall 'Christmas Tree' antenna. Each station will also have 24 'SMARTboxes' scattered in amongst the antennae, connected to a distribution hub near the station. A SMARTbox needs to provide a little DC power to 10-12 antennae, cut that power within a millisecond or so if there's a short, and convert the analogue electrical signals from the antennae to analogue optical over fibre. It also needs to allow remote, high-level telescope software to monitor the temperatures, voltages, currents, etc, and switch antenna on and off.

The problem is that the SKA is so sensitive, any signal from space would be completely drowned out by the electrical noise from a CPU, even a microcontroller, or any normal kind of communications cable (wireless links are obviously COMPLETELY ruled out). The Power and Signal Distribution system (PaSD) has been designed to use low-speed microcontrollers inside multiple layers of shielding, communicating via the Modbus protocol over a custom-designed multidrop serial bus. This multidrop bus links all 24 SMARTboxes in a station into the same address space via 19,200 bits/second serial over the same coaxial cables carrying 48V DC to the SMARTboxes. Python code running on a remote server can then address each SMARTbox, manage power to each antenna, and even push new firmware to the boxes.

In this talk I will describe the PaSD system and its design process, and how I used Python to create simulated SMARTboxes on a simulated multidrop serial link, then used them to validate hardware and firmware prototypes over the last few years. I'll also show live telemetry from a four-SMARTbox system that has been running in the desert at the SKA site for the last year.

Andrew Williams he/him

I’m an optical astronomer who moved from research into software for telescope and instrumentation automation, and I've been working on the Murchison Widefield Array (a large radio telescope in the Murchison region of Western Australia) and related instrumentation since 2007. I work for Curtin University, in Perth, Australia.