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Dissemination

 

ComLab-USB, advanced data acquisition and control system

Updated: 20. April. 2004

Bostjan Murovec
University of Ljubljana, Faculty of Electrical Engnineering
Laboratory for Industrial Electronics and Computer Integrated Manufacturing
e-mail: bostjan@lie.fe.uni-lj.si

The ComLab-USB printed circuit board from top and bottom side.

Chracteristics

Interconnection with the PC

Full-speed (12Mb/s) USB communication with host computer.
External power supply (12 V, AC, >0.5 amp).

A/D subsystem

-          Two channel 12-bit A/D subsystem with 5MHz sample rate,
-          Channel One multiplexed with 8 analogue inputs (6 in range 0V to +5V and 2 in range -10V to +10V) with possibility to sample 1, 2, 4 or 8 inputs,
-          Multiplexing sequence can be original (IN1, IN2, IN3,) or reverted (IN8, IN7, IN6, …).
-          That it is possible to sample (with one channel only):

1.         one input in range 0V to +5V (sampling one input with original sequence)
2.         one input in range –10V to +10V (sampling one input with reverted sequence)
3.         two inputs in range 0V to +5V (sampling two inputs with original sequence)
4.         two inputs in range –10V to +10V (sampling two inputs with reverted sequence)
5.         four inputs in range 0V to +5V (sampling four inputs with original sequence)
6.         two inputs in range 0V to +5V and two inputs in range –10V to +10V (sampling four inputs  with reverted sequence)
7.         six inputs in range from 0V to +5V and two inputs in range –10V to +10V (sampling eighth inputs regardless of the sampling sequence)

-          Channel two intermixed with 8-bit digital input (either of them can be active at a time),
-          Sampling frequency adjustable to 10MHZ / N, where N = 2, …, 65535,
-          Possibility to sample (i.e. transfer to host) only 8 bits, where transfer rate is more important than the sampling accuracy,
-          On-line sampling where each sample is directly transferred to the host,
-          Off-line sampling where samples are written to static RAM and transferred to the host at a later time,
-          The size of static RAM can be selected from 512k, 256k, 128k, …, 4k X 12bit,
-          Possibility of transferring partial parts of static RAM to the host

D/A subsystem

-          Two channel 12-bit D/A subsystem with 2.5MHz excitation rate (slightly over specified – on 2.5MHz some spikes appear on the output signal),
-          Possibility to excite (i.e. transfer from host) only 8 bits, where transfer rate is more important than the excitation accuracy,
-          Both channels provide simultaneous output in ranges 0V to +5V, –10V to +10V and –5V to 0V,
-          Channel two intermixed with 8-bit digital output (either of them can be active at a time, the other one is guaranteed to preserve its value at the time of a switch),
-          On-line sampling where each sample is directly transferred from the host (A/D must also work in on-line mode),
-          Off-line sampling where samples are read from static RAM which is filled with values from the host at a previous time (A/D must also work in off-line mode),
-          The size of static RAM can be selected from 512k, 256k, 128k, …, 4k X 12bit independently of A/D static RAM size,
-          Possibility of transferring values to static RAM per partes,
-          Excitation frequency can be the same as A/D sampling frequency or halved,

Trigger (for off-line mode of operation)

-          Source can be A/D channel one, A/D channel two, external or none,
-          Threshold adjustable at 8-bit accuracy within range of operation,
-          When multiplexed A/D channel is selected as source it is possible to trig within ranges 0V to +5V or –10V to +10V by selecting original or reverted sequence of sampling,
-          Four modes of operation:

1.         Wait for trigger and fill whole Static RAM bank with samples,
2.         Start sampling immediately, fill whole Static RAM bank with samples with circulation and stop sampling at a trigger,
3.         The same as previous mode, except: do not stop at a trigger but some times later (the approximate number of additional samples can be specified to be 2048, 4096, …, 262144),
4.         No trigger: start D/A and A/D subsystem simultaneously and stop sampling at the end of the bank

Here is how the system looked before designing the printed circuit board: