Digital Logic and Computer Lab EEL3701L Lab #8 1 Minute Clock UWF ECE Due: 09 July 2014

Abstract:

The purpose of the lab was to learn how to use data sheets and information given in them to design and create a one minute clock.

Introduction/Background/Theory:

When designing and creating things sometimes the materials needed are not always readily available to use, for example a function wave generator to generate the clock input needed for the flip flops. In this lab the 555 timer will be used to supply the clocking mechanism that is needed. Looking at the data sheets and reading them is very helpful in understanding what it is that is given, from there arrangements to the design can be made to make what is needed using the supplied materials. In the 555 timer:

Figure 1: 555 timer schematics info.

Reading the data sheet schematic for the 555 timer, equations are given to calculate the frequency. In this way one can calculate how fast the pulse is generated and supplied as a clock. From the equations the frequency can be set by changing the values of the resistors and capacitors. Another important part

of the lab is the counter chip. The 74LS163 is a 4-­‐bit binary counter which counts from 0-­‐15 or (0000 to 1111). Using two of these chips one can make a timer, one counter that counts up to 9 (the ones place) and one timer that counts up to 5 (the tens place).

Figure 2: Counter chip diagram

In the counter chip diagram, pins 3,4,5,6 are set to low, that is these pins are the input on which number to start.( i.e. starting at all pins set to low starts at 0 0 0 0 Which starts at 0, or all pins set at high, the count will start at 1 1 1 1, or 15.) pin 2 is the clock, which is supplied by the 555 timer in this case, or a function wave generator. Pin 1 is the clear, when clear = 0, the outputs will go to 0000 at the next clock input. Pin 9 is the load, when load=0 the output will be what the input to A, B, C, D is at the next clock input. Pins 7, 10 are the enable pins, these pins allow the 163 to count. In order for the counter to increment, load, clear, p and t have to be set to 1. If load and clear=1 and either p or t are set to 0, the clock will hold. Pins 11,12,13,14 are the outputs of the chip this outputs the next number in the sequence. Pin 15 is the ripple carry output if overflow occurs. Pin 8 is ground and pin 16 is power.

Procedure:

1. Using the 555 timer and the counter 74LS163, and 74LS47 BCD to 7 segment display decoders, design and build a one minute clock. 2. the timer will provide the clock inputs, the counter will count, and the BCD will provide the outputs to the 7 segment display. 3. a dipswitch is also going to be needed to be able to reset the timer to 0 0 whenever wanted.

Discussions:

1. Read thru the data sheets for the 555 timer. It is a very versatile chip. List at least 3 other functions that the chip can be configured to perform, and briefly describe what each of those functions do/are for. -­‐Monostable operator where a trigger is used and the timer works as a one-­‐shot function, can also act as a frequency divider that can be generated using a divide by 3 circuit. Lastly it can also act as a pulse position modulator where the pulse can be varies with the modulating signal. 2. What is the difference between a synchronous and an asynchronous input to your counters? -­‐synchronous transmissions are synchronized by a clock, as in asynchronous transmission are synchronized by other means not using a clock.

3. If you were to add a minute digit to your clock, how and when would you clock it? -­‐a minute clock would go up to 9 and then would need another display to display a tens minute place. It would clock after the reset of 5 and 9, as those reset the counter would clock and add a 1 to the one minute digit. 4. Discuss, in detail, how you configured the 555 timer to get the proper frequency. After using the equations on the data sheet, did you have to make any adjustments to get you frequency closer to the value you were looking for?

What happened to the resulting frequency after you plugged the 555 clock signal into your circuit (ie, after you loaded down the output of your 555 timer)? -­‐I used my resources and found a calculator online that would help calculate the values of the frequency depending on the capacitor and resistors that I used. As the output was loaded the frequency sped up some but not enough to be significant. 5. Create your own experiment: What does the effect of loading the output of your 555 timer have on the frequency it generates? Use different load values. Also test the results as you vary Ra, Rb, and C (i.e., what happens to the frequency if you raise and lower Ra, Rb, and C individually?). Since you are dealing with 3 values (Ra, Rb, and C) to set the frequencies, there are many different sets of values that will give you the same frequency. Experiment to find out whether or not it is best to use large values of resistors or smaller values. Don’t forget to include a load. Include a table showing the various resistor values that you used and the resulting frequency that they generated.

Conclusion: This lab was to create a one minute counter demonstrated the use of the 555 timer and the 163 chip. It also showed the importance of the data sheets in the information that is given in them. This helped create timer that helped supply the function wave needed instead of having a wave generator, made the designer be resourceful in designing a design with materials that didn’t exactly gave the designer what was needed.

Pre-­‐lab:

Figure 3: logic works design for the one minute clock with reset dipswitch