This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The second milestone in the development of a real-time control (RTC) system for pulsed and FT-ESR spectroscopy was recently passed. The system comprises all basic features required for a pulsed ESR spectrometer timing system with a cost of under $2,500. This system is much more advanced compared to earlier versions. It features small size and low power consumption. RTC capacity is provided by a processor board of our design based on SHARC DSP, which coordinates the functions of several hardware cards via a proprietary 160 MB/s bus. All cards are multi-layer PCBs designed and fabricated at ACERT using surface-mount technology. The latest version can supply pulse sequences of up to 8 pulses with phase cycling at repetition rates of up to 500 kHz. The pulse sequence can update in 10-20 microseconds, and is thus capable of fast sweeps limited only by the digitizer residing in the PC host. Currently, communication between the host PC and the DSP is based on the RS232 interface. A USB2.0 or proprietary serial high-speed link is under development. Our future plans are to use a faster DSP processor from Analog Device with companion FPGA to remove some control tasks from the DSP, which will then be tasked with control over pulse sequence timing and synchronization with the data capture process in AP240. The DSP memory will be increased to hold fine adjustments for every time step of the pulse sequence. Spectrometer control is based on a GUI written in Visual C++. A custom feature of the AP240 provides external control lines for switching between addition and subtraction. This feature will allow us in future work to capture the whole 2D-ELDOR signal in 20 ms and accumulate it in real time as required in stop-flow and continuous flow experiments on protein folding.
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