A) In this lab, you will have an opportunity to analyze and experiment with a circuit based on the 741 operational amplifier.

Bring to lab: Power supply, protoboard, chips (741 op amp), and textbook.

741 Op Amp

You have a 741 integrated circuit in your lab kit. This chip is a "dual in-line package" (DIP), and its pins have the following functions (the notch on the chip helps you orient it properly):

Figure 1: Pin diagram for 741 op amp.

The op amp is powered by two supply voltages, denoted by +V and -V in Figure 1. The values for V can be anything between 3 and 15 volts. However, recall that the output voltage can never exceed the range of +V or -V. We will use V = 12 volts, since your power supply contains +12 volt and -12 volt values.

The 741 op amp can be configured as an inverting amplifier by connecting it as shown in Figure 2. The numbers indicate the pin connections on the op amp.

Please do the following exercises with the circuit in Figure 2.

1. Understand the analysis that leads to the expression .

   Please work through the analysis without referring to the book and be sure you understand the reasoning.

2. Test your circuit.

B) Earlier you examined a circuit that used a thermistor to sensor temperature and convert a temperature signal into a voltage signal. The output of the bridge circuit you constructed was taken between two nodes, neither of which was the ground node in your circuit.

Imagine that you have such a bridge circuit, and that you also have a recorder that needs to have a voltage with respect to ground. You need to convert the voltage difference in the bridge to a voltage with respect to ground. Looking through the texts, you find the circuit below:

This circuit is a differential amplifier. It is supposed to produce a voltage that is proportional to the difference between the two input voltages, V_a and V_b. Would you please understand where the output relation comes from?

In this lab our goal is to design a circuit that will produce a five volt voltage change when the thermistor undergoes a change from room temperature to body temperature.

Use of values of 1k ohms and 10k ohms for R₁ and R₂. Use all combinations of 1k ohms and 10k ohms for R₁ and R₂ as you answer the following:

Why are the voltage followers included in the above circuit?

Now look back in your lab notebook and build the bridge circuit and a differential amplifier to meet our goal.