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Department of Technology

Southwest Texas State University

TECH 4374:  Digital Electronics

Lab Activity 1:  Digital Protoboard

Names__________________________________________

Date____________________

Score____

Objectives:  To gain familiarity with the Heathkit/Zenith ET-3200 digital protoboard,
and to construct a diode-matrix logic circuit to convert decimal numbers
to 2-bit binary numbers.

Materials and equipment needed: 

ET-3200 digital protoboard

Oscilloscope

Digital voltmeter (DVM)

Small-signal silicon diode (1N4001 or equiv.)

Two clip-lead to banana-plug insulated wires (one red, one black)

Insulated wires for protoboard connections

Procedure:  The digital protoboard is a type of breadboard with features
that make it especially useful for building and testing digital logic
circuits with ICs.  It contains a power supply to provide +5 V,
logic and data switches that provide digital outputs, a clock that generates
a square wave, and logic indicators.  By the end of this lab you
will have used all these functions, and will construct a simple diode-matrix
decimal-to-binary converter.

A.   Data Switches, Logic Switches, and
Logic Indicators

1.  Take the ET-3200 digital protoboard from storage and plug
it in (be sure the power strip is turned on).

2.  Plug the red clip lead into the + V input of the DVM and
plug the black clip lead into the ground or common input of the DVM.

3.  Turn on the DVM and set it to read DC voltages in the 0-5
V range.

4.  Connect a wire to the terminal block on the Power Supply
section of the protoboard by inserting its bare end into one of the
holes in the block until you feel it give slightly.  This indicates
that the spring inside the block has a firm grip on the wire and it
has made good electrical contact.

5.  Connect this grounded wire to the black (-) wire of your
DVM.

6.  Connect a wire from the terminal block of Switch 1 in the
Data Switch section to the red (+) lead of your DVM. 

7.  For each setting of Switch 1 (UP and DOWN) record the voltage
at its terminal:

Switch 1 UP:  _________ V

Switch 1 DOWN:__________V

8.  Repeat step 7 with switches 2, 3, and 4, and fill in the
results below:

Switch 2 UP:  _________ V

Switch 2 DOWN:__________V

Switch 3 UP:  _________ V

Switch 3 DOWN:__________V

Switch 4 UP:  _________ V

Switch 4 DOWN:__________V

Remove the wire connections to the DVM.

9.  Connect a wire from Switch 1s terminal block to the leftmost
terminal block in the Logic Indicators section.  Observe the corresponding
indicators state when Switch 1 is UP (logical HI) and DOWN (logical
LO):

HI:  (light on or off?)_______

LO: (light on or off?)_______

10.  Repeat step 9 with the three other logic indicators. 
Do they all work the same?  (yes or no):________  When all
you need to know is the logic state of a line (wire), you can use the
logic indicators instead of a DVM.

11.  Remove all wires from the protoboard.

B.  Clock and Line Source Outputs

12.  Disconnect all wires except the one going to ground on the
Power Supply section.  Connect it to the ground input terminal
of Channel 1 of your oscilloscope.

13.  Set the Channel 1 input to DC, the gain to 1 V/div, and
the timebase to 0.1 sec/div.

14.  Turn on the scope and connect the Channel 1 input to the CLK output of the Clock section. 

15.  Connect another wire from the CLK output to an input of one of the logic
indicators.

16.  Set the Clock switch to 1 Hz.  Observe that the waveform
on the scope moves high or low as the logic indicator light blinks on
and off.

17.  Set the Clock switch to 1 kHz.  What does the logic
indicator light do?_____________________________________________________________________________________________________________________________________________

18.  Change the timebase on the scope to 1 msec/div.  What
is the approximate period T of the Clock waveform now?T =__________ msec.

To measure the high and low voltage levels, temporarily switch the
Channel 1 input from "DC" to "GND".  This is
your 0-volt reference.  Use the vertical position adjustment to
move the trace to the bottom of the screen.  Now when you switch
back to "DC," you can measure the high and low voltage levels
with respect to 0 V at the bottom of the screen.

What is the voltage corresponding to a high logic level?  ________
V.

What is the voltage corresponding to a low logic level?  _________V.

19.  Set the Clock switch to 100 kHz and change the timebase
to 2 sec/div.  What is the approximate period T of the Clock waveform now?T =_________ m</span>sec.

20.  Move the wire that goes to the Channel 1 input from the
Clock output to the terminal marked with a square wave in the Line Source
section.  Does its period correspond to a frequency of about 60
Hz?  (yes or no)____________

C.  Diode Matrix Decimal-to-Binary Circuit

For this
part of the lab you will use the bottom area of the protoboard that
looks like this:

Fig. 1

In areas A and B there are columns of five holes each.  All
the holes in each up-and-down column of five holes in area A are connected
together as shown by the dashed lines.  For example, each hole
in column A1 is connected to all the other holes in column A1. 
That means any wire or circuit element inserted into any of the holes
in A1 will be connected to anything else inserted into A1s holes. 
Therefore, you can connect up to five different wires or part leads
together by using the holes in column A1.  But A1s holes are insulated
from (not connected to) any other hole.  In particular, none of
the holes in region A are connected to any of the holes in region B
below.  There is a groove between regions A and B.  The protoboard
is designed so that ICs will fit across the groove.  For example,
if you inserted an 8-pin IC (4 pins on each side) across the groove
between columns A1-A4 and columns B1-B4, each of the ICs 8 pins would
connect to a column.  In this way you can connect one or more wires
or other parts to each pin of an IC.

21.  The problem you will deal with in this part of the lab is
to convert a decimal representation of the numbers 0, 1, 2, and 3 to
their binary equivalents.  This problem might arise in a situation
such as this one:  An item of equipment originally had a control
panel which had one switch button each for the numbers 0, 1, 2, and
3.  The four wires from these switches must now be interfaced with
a digital system that needs this data in binary form.  Using your
knowledge of binary arithmetic, complete the following truth table by
writing 0 or 1 in eac