Created it, 06/10/19
Update it, 06/10/23
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In this 3rd practice, you will carry out the assembly of the group of switches and will carry out experiments on the circuits OR, NOR and OR Exclusive.
1. - PREPARATION OF THE COMPONENTS
To carry out the exercises envisaged in this practice, you will use the following components which you eûtes in your possession :
4 switches (switches 1 circuit - 2 positions), “to
see figure 1”
1 integrated circuit MM 74C32,
1 integrated circuit MM 74C02,
1 integrated circuit MM 74C86,
1 roller of welding,
1 integrated circuit MM 74C00
which you had at the time of the preceding lesson (2nd
practice). You will be useful yourselves thus of a few pieces of isolated
rigid wire already used in the preceding experiments and will prepare you the
new ones by taking them on the braid in your possession.
2. - ASSEMBLY OF THE GROUP OF SWITCHES
To carry out this work, respect the following indications :
Take a switch and place it on the printed circuit so
that the visible notch on the cylindrical higher part is turned on the side
opposed to inscription SW0 as clearly
indicated figure 1-b.
After you to be assured that the switch is well
inserted into its place and while maintaining it well in contact with the plate,
carry out the welding of the 7 terminals.
By using the same method, lay out the 3 other
switches with their respective site located on the printed circuit by initials SW1,
SW2, SW3 and carry out the welding of the terminals on the
corresponding copper pastilles.
2. 1. - CONTROL NOT UNDER TENSION
Before carrying out this control, you ensure that the four switches are well directed in the way indicated figure 1-a. Check that the weldings are carried out correctly.
Carry out then the following operations :
Lay out the levers of the four switches in manner
that they are directed all the four towards symbol 0
deferred on the printed circuit as you see it in the figure 1-a.
Prepare the controller for the measurement of
resistance gauges W x 1000.
Put a test probe on one of the contacts of the group of connectors located by
the sign “-” and with the other point
touch contact SW0 of the group of connectors.
The needle of the apparatus must indicate a value of null resistance.
By maintaining the test probes on the same contacts,
move the lever of switch SW0 towards symbol 1
; the needle must indicate in this case a value of infinite
resistance.
Now move the test probe which is on the contact “-”
and put it on one of the contacts “+” by
leaving the other point on contact SW0
; the apparatus must indicate a value of null resistance.
By maintaining the test probes of the controller on
one of the contacts “+” and on contact SW0,
put switch SW0 on the position located by
symbol 0. The needle will indicate a value
of infinite resistance.
With these tests, summarized in the points of measurement 1 and 2 of the table of figure 2, you finished the control of switch SW0.
Same manner, check successively switches SW1, SW2, SW3 while carrying out in the order indicated on the table of figure 2, measurements between the various points specified in the second column and by laying out the lever of the switch concerned alternatively on the positions 1 or 0 as indicated in the third column.
If one of the points of control did not give the result indicated in the last column of the table of figure 2, re-examine the assembly. Control the exact provision of the switches, the weldings carried out and ensure you that there are no cut tracks or short-circuit between close tracks.
When you obtain correct measurements for each switch, you will be able to carry out the operational test.
2. 2. - OPERATIONAL TEST
To carry out this test, you conform to the following instructions :
lay out the levers of the 4 switches on position 0.
by using 4 pieces of rigid wire isolated from 10 cm each one, connect between
them the points of the group of connectors indicated below and illustrated
figure 3.
Contact SW0 with the L0 contact
Contact SW1 with the L1 contact
Contact SW2 with the L2 contact
Contact SW3 with the L3 contact
feed then the circuit, connect the cords red and
black to the pile ; the four LED located by L0,
L1, L2 and L3 remain extinct.
move then the levers of the switches on position 1
; in this case, the LED L0, L1, L2
and L3 ignite.
You now controlled the operation of the group of switches whose electric diagram is deferred in figure 4.
The two positions, which the common contact of each switch can take, are located by symbol 1 and 0. Symbol 1 is associated the position making available on the group of connectors a “high” level of tension (+ 4,5 V), while the position represented by symbol 0 corresponds to a level of low tension (0 V).
You can, now, carry out the experiments practice of which the goal is to give the opportunity to you to familiarize you with the characteristics of the basic components used in the digital circuits.
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