10 Laboratory Three Clocks and Oscilloscopes Warning: This laboratory involves more work than the previous laboratories, so budget your time carefully. Also, save the clock circuit produced in this laboratory for use in future labs. Objectives The main objectives of this laboratory are: Construct and observe the properties of digital clock circuits Introduce the use of the oscilloscope for viewing digital signals Observe the switching characteristics of basic logic gates Activities The first activity in this laboratory is to build a square wave oscillator. A square wave oscillator produces a signal that looks like a sequence of squares (thus, the name). The signal starts at the low level, then after a short period of time switches to the high level, and then after a short period of time switches back to the low level. The time between adjacent low levels is the period of the oscillator, which is 1/frequency. Square wave oscillators are common in digital electronics, since the low level can represent 0 or false, and the high level can represent 1 or true. These signals can be used to synchronize different parts of a circuit and coordinate different components in a computer system. There are many ways of producing a square wave oscillator, in our case we will base it on an LM358 dual operational amplifier, which is included in the parts kit that comes with the oscilloscope (thus, we don’t need to buy any extra parts). This is a reasonable approach in our case, since it illustrates a number of the characteristics of digital circuits that we are interested in. But, we would normally use a part that would give us a higher frequency. This particular type of operational amplifier is quite popular and is produced by a number of semiconductor companies. National Semiconductor has a very good data sheet for this part and the square wave oscillator that we will use is based on the information in this publication. The LM358 is an 8 pin chip and as the name indicates it contains two operational amplifiers. We will only use one of the operational amplifiers. You will find the LM358 in your laboratory kit in the dark plastic bag, and it is mounted on a piece of black foam. Be careful to get the right chip, there are two small chips on this piece of foam. Place the chip near the top of the breadboard, since we will want to use the oscillator in several laboratories.