ECE 323L Basic Electronic Circuits Laboratory

Lab 10

 

 

Name:

 

 

 

Do the following exercises. Report your results by editing this Word document and submitting it in WebCT.

 

This laboratory is the third in a series of experiences using digital electronic components. You will use a 7805 voltage regulator chip to convert your 9-volt battery supply to a 5-volt supply from the last two weeks and the seven-segment display from last week.

 

  1. Interface a counter based on a 74LS90 chip to your seven-segment display. Use a 555 timer circuit (see lab 5) to trigger the counter (pin 14).  Demonstrate the circuit to the lab assistant.

 

Figure 1. Pin diagram of LS7490 chip

 

 

Figure 2. Circuit for simple decimal counter

  1. Measure the period of your 555 timer using the oscilloscope. Measure the period of the counter by using a watch to time a fixed number of counts (ten or more). Note that noise may cause the counter to update more frequently than the timer, at least it did on my breadboard.

 

 

Measured Period

Timer

 

Counter

 

 

  1. (Optional) Try to trigger the counter manually by connecting and disconnecting pin 14 to ground. Chances are you will observe contact “bounce”, the counter will make several steps instead of one.

 

  1. (Optional) Connect your counter to the output of your SR-flip-flop. By first setting and then resetting the flip-flop you should be able to make the counter increment cleanly.

 

 

maintained by John Loomis, updated 24 March 2008