Generator
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Created it, 06/10/19
Update it, 06/10/29
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8. - FIFTH EXPERIMENT : REALIZATION OF A STOP WATCH
In this experiment, the bill-posters will use to produce a stop watch which can count up to 99 seconds.
8. 1. - REALIZATION OF THE CIRCUIT
a) Remove all the connections and the components relating to the preceding experiment.
b) Insert on the matrix, the meter modulo 16 MM 74C163, the decoder 4 entries - 10 exits MM 74C42, the integrated circuit MM 74C00 (quadruple NAND), the decoder 4 entries - 16 exits MM 74C154 and the synchronous meter with 4 bits MM 74C193.
c) Carry out the connections indicated to the figure 25-a.
As this assembly comprises a high number of connections, use wire of different colors and proceed to wiring with attention.
You can make sure that the circuit carried out reflects well the electric diagram of the figure 25-b.
You notice that this electric diagram starts to be rather complex.
Indeed, it includes/understands already five integrated circuits, and the total comprehension of the circuit requires a certain deliberation.
Also, in electronics, one generally uses synoptic diagrams which allow a comprehension much easier circuits.
Figure 26 represents such a synoptic diagram. It is that of the circuit which you have just carried out.
The fundamental difference compared to the electric diagram is the radical reduction in the number of the connections.
In this synoptic diagram, you notice that there are two types of connections. One is represented by a single line, the other by two parallel lines ending in an arrow.
A single line represents only one electric driver (only one connection). Two parallel lines represent a standard whole of connections in the same way. It is the case of the four exits of the meter of the units.
Sometimes, the number of the connections is indicated. It is always the case of figure 26 with the four exits of the meter of the units.
It is possible to analyze the operation of the circuit starting from this synoptic diagram.
The meter of the units is incremented at the rate / rhythm of a unit every second. When it arrives at 9, exit 9 of the decoder which is attached to him applies a logical level L to entry CLEAR.
To the tenth active face of the clock, the meter of the units thus passes to 0 and the meter of tens passes to 1 and so on. To each time the meter of the units passes from 9 to 0, that of tens is incremented of a unit.
Indeed, exit 9 of the decoder of the units passes on the level L on the level H and thus causes active face going up on entry CLOCK of the meter of tens. Parallel to the incrementing of the two meters, two bill-posters DIS0 and DIS1 indicate the figures located at exit of the two meters.
8. 2. - OPERATIONAL TEST
a) Put SW0 on position 0.
b) Put the digilab under tension.
The two bill-posters indicate 00, because entries LOAD of the two meters being on the level L, the meter of the units is prépositionné to 0 at the time of the first positive face of signal CP1 (the meter of tens is given to 0 instantaneously).
c) Bring back SW0 on position 1. From this moment, the stop watch starts to count the seconds which are passed. Bill-poster DIS0 indicates the seconds and bill-poster DIS1 tens of seconds.
When the meter arrives at 99, it passes by again to 00 with the blow of clock according to.
d) Support on P0 during a few seconds. You observe that the bill-posters remain blocked.
e) Slacken P0. Counting begins again, not starting from the number on which it stopped but starting from the real number of seconds which were passed since the beginning of counting.
Indeed, while supporting on P0, the entries LATCH LE0 and LE1 are activated and the number present at this moment is memorized. However, counting continues, which explains why when you slacken the P0 button, the bill-posters indicate the real number reached by the stop watch to this moment.
f) Put SW0 on position 0. The stop watch thus passes by again to zero.
g) Put the digilab not under tension.
This experiment enabled you to see that it is possible to produce a stop watch using specific integrated circuits.
The principle used in the digital watches is the same one. Two differences resident in the fact that an oscillator with quartz is used in the numerical watches and the fact that the level of integration of the logical circuits is very thorough. In the experiment that you carried out, you use of the integrated circuits standard and universal, whose applications can be multiple, and for this reason your assembly occupies a certain considerable volume.
Now let us analyze in detail the operation of this assembly.
When SW0 is positioned on 0, meter MM74C193 charges the binary number present on its entries, that is to say 0000 in this case.
The meter of the units charges the same binary number 0000 with the active face of the clock since entry LOAD is synchronous.
As long as SW0 remains on position 0, the meter of the units is in loading mode and consequently load permanently 0000 with each active face of clock.
As soon as SW0 is brought back on position 1, the stop watch starts to count the seconds which are passed.
Indeed, the meter of the units is incremented from 0 to 9, to 9 exit 9 of decoder MM74C42 passes on the level L ; however, this exit is connected to synchronous entry CLEAR of the meter of the units and to entry COUNT UP of the meter of tens.
Thus to the tenth active face of clock, the meter of the units passes to zero since entry CLEAR is on the level L. the bill-poster DIS 0 thus indicates figure 0. At the same time, exit 9 of decoder MM74C42 passes by again with the state H and consequently, the meter of tens is incremented of a unit and thus passes to 1.
Counting continues thus up to 99.
With the hundredth active face of the clock, the meter of the units thus passes by again to 0. The meter of tens passes to 10 and exit 10, from decoder MM74C154 thus passes to 0 simultaneously. Thus asynchronous entry CLEAR of the meter of tens is activated and this meter passes by again immediately to zero.
Thus in fact, the stop watch passes in an almost instantaneous way of 99 to 00.
Exit 10 of decoder MM74C154 remains only a few tens of nanoseconds on the level L.
Figure 27 represents a chronogram of the operation of the stop watch relating to the two exits of the two decoders.
This stop watch also constitutes a meter modulo 100.
9. - SIXTH EXPERIMENT : REALIZATION Of a GENERATOR OF RANDOM
NUMBER RANGING BETWEEN 1
AND 90
You now will carry out a circuit which, once actuated, automatically posts a number ranging between 1 and 90.
This circuit is of course a meter whose operation is based on the same principle as that of the preceding experiment. It differs only by the fact that it counts up to 90 instead of 99 and that it sets out again of 1 instead of 0.
9. 1. - REALIZATION OF THE CIRCUIT
a) Remove last circuit carried out the connections indicated in dotted on figure 28.
b) Remove matrix the integrated circuit MM 74C00 and put at its place the integrated circuit MM 74C02 (quadruple NOR).
c) Insert on the matrix the diode 1N4148, an electrolytique capacitor with the tantalum of 1 µF (respect the polarity of its terminals) and a resistance of 1 MW as indicated in figure 29.
d) Carry out the connections represented in black on figure 29.
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Figure 30 represents the electric diagram and the synoptic diagram of the circuit carried out. These two diagrams differ from those of the stop watch by the presence of the network including/understanding the NOR doors A, B and the door NOR C.
The network including/understanding the doors A and B is charged to ensure the randomness of the pulling of the number.
The door C makes it possible to put at zero the meter tens when the four-twenty-eleventh clock pulse arrives.
9. 2. - OPERATIONAL TEST
a) Connect the food: the bill-posters indicate a random number ranging between 1 and 90.
b) Support on P0 : the meter is incremented at the frequency of 100 Hz. You thus see ravelling the numbers on the two bill-posters.
c) Slacken P0 : at the end of a certain time, the two bill-posters immobilize themselves on a number which is the result of pulling.
Each time you actuate P0, you carry out a new pulling.
d) Disconnect the food.
The circuit examined with the same structure as that of the fifth experiment. Separately the fact that it counts from 1 to 90 instead of 0 to 99, it does not comprise restoring initial.
So that the meter passes from 90 to 01, it is enough to decode number 91 and to make a restoring of the meter of tens.
Decoding is ensured by the NOR door C which receives the signals of exit 9 of the decoder of tens and exit 10 of the decoder of the units.
When these two exits pass on the level L, that indicates that the meter incremented up to 91. Thus, the exit of the NOR door C passes on the level H and thus carries out a restoring of the meter of tens by entry CLEAR.
The meter being asynchronous, the circuit remains with state 91 during a short moment to pass almost instantaneously to state 01, as one sees it on figure 31.
The purpose of the two other NOR doors A and B, jointly with a cell RC and a diode, are to make pulling more random.
When one supports on P0, one applies a level H to the entry of NOR door A. This door being cabled out of reverser, one finds at his exit a level L which validates the NOR door Thus B. the clock signal of 100 Hz provided by CP1 is found reversed at the exit of the NOR door B and increments the circuit made up of the two meters.
When P0 is slackened, the input voltage of door A does not fall immediately because the condenser of 1 µF spends a certain time to discharge in resistance from 1 MW.
The exit of door A will pass on the level H only when the terminal voltage of the condenser goes down in lower part from the threshold from commutation from this door.
Consequently, the clock signal of 100 Hz will not be able to cross any more the door B and counting will thus stop.
Pulling is doubly random. First of all that which supports on P0 cannot know with which number the meter arrived (the figures of the bill-posters ravel too quickly), then the discharge of the condenser introduces an additional indetermination.
In the next practice, the circuits summoners and the multiplexers will be examined.
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