ECE 323L Basic Electronic Circuits Laboratory

Lab 8

 

 

Name:

 

 

 

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

 

This laboratory starts a series of experiences using digital electronic components. These components have strict requirements on power supply voltage. You will use a 7805 voltage regulator chip to convert our 9-volt battery supply to a 5-volt supply. Then you will explore some digital operations that use nand gates.

 

 

  1. The 7805 is a voltage regulator that puts out a constant 5V DC, for an input voltage between 7 and 25V DC. The 7805 comes in a T0-220AB package with three pins that can be plugged into the breadboard.  These three pins are Output, Ground, and Input. The picture on the right shows how a 7805 might fit into a breadboard. The capacitor shown on the right is a decoupling capacitor, which stores power for use during logic switching operations. Use a value between 0.1 mF and 1 mF. Connect the negative end of the capacitor to ground.

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Use your multimeter to measure the output of the voltage regulator and record your reading here.

 

 

Voltage

 

 

 

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  1. Find a 74LS00N chip in your tackle box. The pin diagram for this chip is reproduced below.

 

 

 

 

Connect one of the nand gates as an inverter, as shown in the diagram below. Connect the output to an LED so that the gate will sink current, as shown.

 

 


Connect the input to 5 Volts (or leave unconnected) for a logic HI and connect the input to ground for a logic LO.  Observe whether the LED is on or off and record your observations here:

 

Input

Output

Unconnected

 

LO

 

HI

 

 

In the above circuit, the NAND gate is wired as an inverter. In the following exercises, the inverter symbol is used, but you use a NAND gate as an inverter.

 

 

 

 

 

 

  1. Disconnect the input leads of the NAND gate so that the inputs may be set separately, as shown below

 

 

Record the truth table for this circuit below, use ON if the LED is lit and OFF if the LED is dark.

 

A

B

Output

LO

LO

 

LO

HI

 

HI

LO

 

HI

HI

 

 

 

  1. Connect two NAND gates together to form the following circuit.

 

 

Record the truth table for this circuit below, use ON if the LED is lit and OFF if the LED is dark.

 

A

B

Output

LO

LO

 

LO

HI

 

HI

LO

 

HI

HI

 

 

Does this circuit correspond to one of our 8 standard gates? If so identify the name of the gate.

 

  1. Connect three NAND gates together to form the following circuit.

 

 

Record the truth table for this circuit below, use ON if the LED is lit and OFF if the LED is dark.

 

A

B

Output

LO

LO

 

LO

HI

 

HI

LO

 

HI

HI

 

 

Does this circuit correspond to one of our 8 standard gates? If so identify the name of the gate.

 

You may see that inserting explicit inverters into a circuit drawing can be difficult. That is why bubble notation is so convenient. The two drawings below are then equivalent:

 

 

 

  1. Connect all four NAND gates together to form the following circuit.

 

 

Record the truth table for this circuit below, use ON if the LED is lit and OFF if the LED is dark.

 

C

A

B

Output

LO

LO

LO

 

LO

LO

HI

 

LO

HI

LO

 

LO

HI

HI

 

HI

LO

LO

 

HI

LO

HI

 

HI

HI

LO

 

HI

HI

HI

 

 

Demonstrate this circuit to the lab assistant for signature verification.

 

maintained by John Loomis, updated 25 February 2008