Lena/Oct 2016: Difference between revisions

There are twoseveral main approaches we can use. The first approach is to have multiple FPGAs, each one controlling a set of four magnetometers. The cheapest NI FPGA (7851R) costs $2.8k, equating is $700/channel. The drawback is that the FPGA only has 8 analog inputs and 8 analog outputs, and there are no analog outputs free for the feedback signals. There are still free digital outputs that the FPGA can use to talk to an Arduino over SPI or something similar. Using FPGAs will result in the fastest feedback with proper timing. We don't have the requirements for the feedback to be fast (its band is DC-0.5 Hz as of now) With the signal normalization the FPGA is already close to its limit of slices.

The second approach is to use a PXI rack with stacks of ADCs and DAQs. The advantage is that we can add DAQs very easily by adding new boards. We could use a dedicated real-time controller to process the data, and if both DAQs and ADCs support NI DAQmx then the real time controller is not really needed. These boards have their own controllers that ensures timing, and the data processing can be done on the host computer. Each sensor running at 20 kHz with 18-32 bit resolution should produce around 1 MBit/second of data, which is very manageable. With a dedicated controller the price would be $500/channel, and if the host does the data processing it's $230/channel. It would be hard to have any reasonably fast feedback with this approach.