ELEC 101, Spring 2005
Prof. Rich Kozick

Laboratory 10
Design of an Analog to Digital Converter (ADC)

Recall that in Laboratory 5 we built a digital to analog conversion (DAC) circuit. This circuit converted a 3-bit binary number into an analog voltage level in the range from 0 volts to 7 volts. One application of the DAC circuit is a digital audio CD player. The CD player converts 16-bit binary numbers into voltage levels that are then played through a speaker.

In this lab, we want to look at a circuit that can be used to record digital music. We need a circuit that can convert a voltage level into a binary number. This process is called analog to digital conversion (ADC). ADC circuits are also used in digital measurement instruments such as the lab oscilloscopes and digital multimeters.

The ADC that you design should convert voltage levels in the range from 0 volts to 4 volts into 3-bit binary numbers as follows:

    Input Voltage      QC  QB  QA
    -------------      __  __  __

     0.0 - 0.5 V        0   0   0
     0.5 - 1.0 V        0   0   1
     1.0 - 1.5 V        0   1   0
     1.5 - 2.0 V        0   1   1
     2.0 - 2.5 V        1   0   0
     2.5 - 3.0 V        1   0   1
     3.0 - 3.5 V        1   1   0
     3.5 - 4.0 V        1   1   1

The parts that you will use include a comparator (LM339), the 74163 counter, the 555 timer, a DAC, and LEDs to display the binary output. (Instead of LEDs, you might use the 7447 and 7-segment display to output a decimal number.)

Lab activities:

  1. Be sure that your stopwatch from Laboratory 9 is working. I will ask you to demonstrate your stopwatch at the beginning of the lab period, unless you showed it last week.
  2. Review the DAC circuit from Laboratory 5.
  3. Include the complete design of your ADC circuit in your lab notebook. Indicate the connections of important pins on the ICs (you don't have to show all of the pin connections), and specify the resistor values in your DAC.
  4. Wire the ADC and demonstrate it.

Note: Several items from your stopwatch are useful for the ADC !

Thank you and have fun.