Ethernet-Based Experiment Control Architecture

Goal: to develop an open-source set of hardware and software tools for controlling experiments, especially in the area of quantum optics and cold-atom physics. The components should be relatively inexpensive, make use of open-source development tools and components, and should not rely on proprietary or archaic technologies (GPIB, National Instruments hardware/software, etc.).

First efforts in this direction are based on the Ethernut controller, which features an Ethernet controller, microprocessor, digital and analog I/O lines, serial ports, and a real-time OS.

Project List:

• A web-enabled thermocouple monitor, useful for monitoring temperatures in the laboratory or to monitor the bakeout of a vacuum chamber. Available so far are a draft description and parts list (pdf) and a draft schematic (pdf).

• An ethernet-interfaced, 16-channel digital output for latching or real-time, high-speed control. Essentially a relatively simple interface between the Ethernut and the digital output board described here. 1 MHz performance should be reasonable using this architecture.

• An ethernet-interfaced, 8-channel analog output for latching or real-time, high-speed control. Essentially a relatively simple interface between the Ethernut and the analog output board described here. 125 kHz performance on 8 channels or 1 MHz on 1 channel should be reasonable using this architecture. Possibly this (and the digital out) could be better done by addressing a separate fast SRAM chip set using a programmable counter for sequential access; then the counter could count the stable input clock signal to give a long, fast 16-bit analog waveform that is independent of the Ethernut capabilities.

• An ethernet-interfaced, multichannel analog input. A simple, non-timed unit will probably suffice for most purposes, although a buffered/clocked version would be a nice replacement for a digital oscilloscope.

• An ethernet-interfaced, programmable DDS RF generator, using the AD9852 or similar device. With an RF power amplifier, this would be a convenient, low-cost, high-precision (in combination with a precise, 10 MHz input) driver for an acousto-optic modulator (AOM). Another design using this device is available here.

• Networked master trigger/delay generator. 16 or so output lines with programmable pulse delay and duration, triggerable with single digital input or via network. One solution is to use an Intersil 82C54 programmable timer/counter (each has 3 16-bit counters). This would allow for 100 ns resolution and delays up to 326 days. This idea is to use one master counter to generate divide-by-2⁸ and divide-by-2¹⁶ clocks from the 10 MHz master clock. Each channel would have its own 82C54, which would act as a set of 3 cascaded interrupt timers (each on a different clock, with the slowest counter triggered first). This would produce a highly adjustable rising edge, while another similarly configured 82C54 would produce the falling edge (the two edges being combined by external, suitable fast logic).

• Networked timer/counter.

• Networked lock-in amplifier.

• Networked feedback-control loop, with pid filter implemented in software for easy configuration without many front-panel knobs. Or possibly analog pid filter with frequencies and gains programmable using Xicor digital pots. Possible as part of integrated diode-laser control system (pid also useful for temperature control).

• Ethernet to RS232 high-level adaptor, for simplifying communication with those pesky commercial boxes. (Certainly beats GPIB.)

• Rubidium or GPS clock with 10 MHz distribution (many buffered outputs).

Resources:

• AVRFreaks.net has a lot of information on programming embedded controllers, including AVR-GCC C Compiler for programming the Ethernut (and other) controller board.

• Information on AVR programming under OS X, including the OS X port of AVR-GCC.

• The Keyspan High speed USB serial adaptor allows programming and communication with the Ethernut via the ISP interface using OS X.