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:
|
