4/09/2015

Today we focused on more operational amplifiers. Although this time we applied cascaded op amp circuits, which is when two or more op amp circuits are connected in a head to tail arrangement.

Circuit Diagram for Wheatstone Bridge

Above is a circuit diagram for a wheatstone bridge. The purpose of the wheatstone bridge is to detect small changes in temperature when implemented with a thermistor and a difference amplifying circuit.

Wheatstone  Bridge Circuit Built and Balanced

The first step of this experiment required us to build a wheatstone  bridge circuit and balance it.

Above is a video of balancing the wheatstone bridge by using a potentiometer. To balance the bridge VG (refer to first picture) should measure a zero potential difference.

Above is a video of our cascaded amplifier in use. As can be seen, when the thermistor is touched the voltage begins to drop, because it detects a change in temperature.

Circuit Built

Above is a picture of our temperature detection circuit. In order to detect changes in temperature we implemented a thermistor in series with the potentiometer. The thermistor is able to detect changes in temperature and as a result the voltage will drop when measuring Vout from the difference amplifier.

Results and Data

Above is the data gathered from the lab.

Summary:

Today, we learned about cascaded amplifiers. A cascade amplifier is a head-to-tail circuit of two or more op amp circuits where the output of one op amp is the input another op amp. For the temperature measurement circuit, a balanced wheatstone bridge is required in order for a fully functioning temperature system. However, a wheatstone bridge requires that the resistors in the circuit to be 100% the same. This is not possible and so this accounts for some error in this lab. We also learned about a digital to analog converter (DAC). A DAC converts digital signals into analog form. This is done by simply using a summing amplifier as discussed in the previous day.