Part A: (30%)
Simulate the system shown in Fig 9.1 using Multisim. Initially set the Variable voltage source VB=1.5V, and ‘open’ the switch and leave it ‘open’. Not an ‘open switch’ is not conducting and a ‘closed switch’ is conducting.
When you open the switch the LED should remain ON, then after a short interval go off. Repeat this sequence by momentarily closing the switch then opening it again. Note that almost instantly the switch is closed the LED comes ON.
Q1. Monitor and record the voltages at pins 2 and 3 of U1, keeping an eye on the LED status. At what voltage on pin 2 does the LED go out? Can you explain why it is no longer ON? Check and record the voltage changes at pin 6 of 741 op-amp (U1) when the LED is ON and OFF.
Q2. Set VB=2V, 4V, 6V and 8V . What happens to the LED for each value and why? Explain what U1 (741 op-amp) is doing?
