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Interactive Lab: A System for Teaching Electronics using an Interface to PSpice
Julio J. González, State University of New York at New Paltz
Laurence Reitman, State University of New York at New Paltz
 

The Shockwave at the end of this page lets you try out how Interactive Lab works.
Depending on your network connection, it may take a few seconds to a few minutes to download this Shockwave.

Introduction: To illustrate Interactive Laboratory, this demo will walk through the steps a student would take in completing a laboratory exercise. This demo will examine the Saw-tooth Waveform Generator laboratory. In the laboratories, a student is expected to compute component values for a given circuit that will satisfy a predetermined set of design specifications. For the Saw-tooth laboratory the circuit used is shown below with the components to be calculated highlighted.

This circuit should generate the waveform v₃(t) from input v₅(t) as shown below.

Ciruit Theory: A constant voltage v₁ = -15 Volts applied to resistor R produces a constant current I = ‑v_1/R circulating R from right to left. The additional path this current will flow depends on the state if transistor Q, which operates as a switch (connected in parallel with capacitor C), driven on and off by square-wave input voltage v₅. When switch Q is open, constant current I flows through C, charging it linearly with time, according to the equation v₃ = I·t/C. When Q is turned off, C quickly discharges through Q, and I flows now through closed switch Q, which makes v₃ remain equal to zero.

With above explanation, and adopting a current I = 10 mA and an over-saturation factor OS » 10 for Q, the student should be able to come up with the following component values: R = 1.5 kW, C = 0.2 mF and R_b = 2.2 kW.