User manual

page 88
Analog System Lab Kit PRO
appendix C
In any analog lab, an oscilloscope is required to display
waveforms at dierent points in the circuit under
construction in order to verify circuit operation and, if
necessary, redesign the circuit. High-end oscilloscopes
are needed for measurements and characterization
in labs. Today, solutions are available to students for
converting a PC into an oscilloscope. These solutions
require some additional hardware to route the analog
signals to the PC for observation; they also require
software that provides the graphical user interface to
convert a PC display into an oscilloscope. Since most
students have access to a PC or laptop today, we have
designed the Analog System Lab such that a PC-based
oscilloscope solution can be used along with ASLK
PRO. We believe this will reduce the dependence of
the student on a full-edged lab. In this chapter, we
will review a solution for a PC-based oscilloscope. The
components on the ASLK PRO can be used to build
the interface circuit needed to convert the PC into an
oscilloscope.
Oneofthesolutionsfora“PCoscilloscope”isZelscope
[33] which works on personal computers running
Microsoft Windows XP. The hardware requirements for
the PC are modest (300+ MHz clock, 64+ MB memory).
It uses the sound card in the PC for converting the
analogsignalsintodigitalform.TheZelscopesoftware,
which requires about 1 MB space, is capable of using
the digitized signal to display waveforms as well as
the frequency spectrum of the analog signal. At the
‘line in’ jack of the sound card, the typical voltage
should be about 1 volt AC; hence it is essential to
protect the sound card from over voltages. A buer
ampliercircuitisrequiredtoprotectthesoundcard
from overvoltages. Two copies of such a circuit are
needed to implement a dual-channel oscilloscope. The
buerampliercircuitisshowninFigureC.1andhas
been borrowed from [32].
C.1 Introduction
Limitations
BNC
C1
0.1uF
R1
1M
C2
20pF
R2
47k 1/2W
C3
100pF
D2
1N914
D3
1N914
R3
4.7k
-12V
D1
1N914
+12V
TI082
RS
27k
R4
3k
R6
100k
RCA
IVoutl<12V
Zin=1M
IVinl<150V
S1
•Not possible to display DC voltages (due to input
capacitor of sound card blocks DC)
•Lowfrequencyrange(10Hz-20kHz)
•Measurementisnotveryaccurate
Figure C.1:
Buer circuit
needed to
interface an
Analog Signal
to Oscilloscope