NOTICE: This webpage and associated files is provided for reference only. This is not a kit site! It
is a collection of my work here at the
University of Toronto in the
Physics department. If you are considering using any schematics, designs, or anything else from here then be
warned that you had better know something of what you are about to do. No design is guaranteed in any way,
including workable schematic, board layout, HDL code, embedded software, user software, component selection, documentation,
webpages, or anything.
All that said, if it says here it works then for me it worked. To make the project work may have involved undocumented
additions, changes, deletions, tweaks, tunings, alterations, modifications, adjustments, waving of a wand while wearing
a pointy black hat, appeals to electron deities and just plain doing whatever it takes to make the project work.
The digital buffer board connects to an
ADwin-Pro "Sequencer", which is a rack mount, stand-alone, programmable controller based on an SHARC 40MHz 21062
or 80MHz 21162 RISC processor, with a Basic-like programming language and a National Instruments interface. The
board is configured as a BNC patch panels that can be mounted above the ADwin. It is reasonably idiot-proof,
primarily protecting the ADwin from transients, EMI/RFI both directions, ESD, grounding potential differences, ground
loops, output conflicts (both ADwin and buffer board configured as outputs).
The Digital board connects to the ADwin via a DB-37 connector and cable. It has 16 output channels (D0:16)
and 16 jumper selectable I/O channels (D17:31). All channels are galvanically isolated from the ADwin up
to 2.5KV, excluding the power supply. All I/Os are via BNCs. Each BNC shield connects to a common potential
through 4.3 Ohms; this shield potential is almost always at ground potential, however the resistance allows for
slight grounding differences between this common potential and the I/O device connected to it. All outputs
are are 50 Ohms, however, 50 Ohm termination is not required and high impedance termination is preferred.
All inputs are high impedance.
Isolation: The basis of the galvanic isolation is the Analog Devices' ADUM1400BRW, a quad high speed
Ouputs: Each channel configured in the ADwin as an output is first isolated with a channel of an ADUM1400BRW,
then into a channel of a Texas Intruments (or other)
(AKA '244) octal 25-Ohm driver, then through 43 Ohms to an output selection jumper (D16:31 only) and finally to the BNC.
The output selection jumpers on channels 16 to 31 enables that channel as an output. The 43 Ohms, in combination
with the '244 inherent output impedance and the 4.3 Ohm shield resistance, provides a roughly 50 Ohm source impedance.
Reflections from high impedance loads will be absorbed by the '244.