Realization and Examination
of a Synchronous Meter of Module 16 |
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Created it, 06/10/19
Update it, 06/10/28
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4. - THIRD EXPERIMENT : EXAMINATION OF A METER OF MODULE 4 CARRIED OUT WITH TWO METERS OF MODULE 2
It is not always enough to divide by 2 : for example, in the digital watches, to obtain a raised precision, one uses an oscillator with very stable quartz, functioning at the frequency of 32 768 Hz. This base frequency is then divided by a meter of module 32 768, so as to obtain a frequency of 1 Hz.
This frequency corresponds to an impulse a second which will be used to order the indicating device of the seconds.
In addition to the seconds, the watch must also indicate the minutes.
It thus uses a meter of module 60 which adds up 60 impulses of 1 second to obtain an impulse each minute.
A second meter of module 60 adds up then 60 impulses of 1 minute to give an impulse every hour.
In this experiment, we will not examine meters of module also raised, but we will increase the capacity of the simple meters of the first two experiments to obtain a meter of module 4.
4. 1. - REALIZATION OF THE CIRCUIT
a) Remove all the connections relating to the preceding experiment while leaving places from there the integrated circuit MM 74C74 on the matrix.
b) Carry out the connections represented with the figure 7-a.
The electric diagram of the circuit carried out is given to the figure 7-b.
4. 2. - OPERATIONAL TESTS
a) Put SW0 on position 0 and energize the digilab : The LED L0 and L1 are extinct, entries CLEAR being active. Let us indicate this state by state 0, thus one can write :
State 0 = L0 extinct and L1 extinct
b) Put SW0 on position 1 : two entries CLEAR are not active any more.
c) Support on P0 : L0 ignites and L1 remains extinct. Let us indicate this state by state 1 :
State 1 = L0 lit and L1 extinct
d) Support one second time on P0 : L0 dies out and L1 ignites. Let us indicate this state by state 2 :
State 2 = L0 extinct and L1 lit
e) Support third once on P0 : L0 ignites and L1 remains lit. Let us indicate this state by state 3 :
State 3 = L0 lit and L1 lit
f) Actuate P0 once again : L0 and L1 die out. The circuit thus returned to the state 0 initial. This circuit is able thus to count three impulses ; to the fourth, it totals zero since its capacity of counting was exceeded.
g) Put not under tension the digilab.
h) Lay out the first generator of clock of the digilab on the frequency of 1 Hz.
i) Remove P0
contact the end of the driver coming from pin 3 of the integrated circuit
MM 74C74 and introduce it into contact CP1
as indicated in figure 8.
In this way you apply to entry CLOCK, either the signal provided by the P0 button, but that generated by the oscillator cabled to the frequency of 1 Hz and visualized by means of L4.
j) Connect pin 3 of the integrated circuit MM 74C74 into the LED L4 as indicated by this same figure 8.
k) Connect the food : L4 ignites and dies out at the rate/rhythm of once a second ; L0 on the other hand, ignites once every two seconds and L1 only once every four seconds.
As the timing chart of figure 9 shows it, the circuit also functions like divider.
At the exit of the first rocker (pin 5), the clock signal is divided by 2 while at the exit of the second rocker (pin 9), this one is divided by 4.
l) Put not under tension the digilab.
As you could note it, by connecting two meters of module 2 in cascade, one obtains a meter of module 4. The same circuit can, moreover, to function out of divider by 2 or 4 according to whether one takes the output signal of the first rocker or the second rocker.
While adding following other meters of module 2, one thus increases the capacity of the counter circuit like dividing circuit.
For example with three rockers, one can produce a divider by 8, with four rockers a divider by 16 and so on.
5. - FOURTH EXPERIMENT : REALIZATION AND EXAMINATION
OF A SYNCHRONOUS METER OF MODULE 16
The meter of module 4 that you carried out in the preceding experiment is of asynchronous type.
Indeed, the two rockers which
constitute it are ordered by two different clock signals. The clock signal of
the first rocker comes from the oscillator with 1 Hz,
while the clock signal of the second rocker is provided by the exit 
of the first rocker. Thus, the second stage of the meter commutates only after
the first stage commutated under the effect of a clock pulse.
If the meter is made of several stages, it is followed from there that each one of them must await the commutation of the precedent to commutate in its turn.
If the commutation of a stage were instantaneous, all the exits of the meter would commutate simultaneously.
Actually, this commutation is done with a certain delay. The transfer time of a stage is thus added with that of the following.
Consequently, between moment when the clock pulse arrives and that where the last rocker commutates, it runs out a all the more long time as the number of stages constituting the meter is high.
In certain cases, that can be a disadvantage which can be avoided by using meters of the synchronous type. Indeed, the rockers of these meters are ordered simultaneously by the same clock signal. Thus, there is no delay of swing between the various stages.
In this experiment, you will examine a synchronous meter of module 16 carried out by means of rockers and logical doors.
5. 1. - REALIZATION OF THE CIRCUIT
a) Remove the connections relating to the preceding experiment as well as the integrated circuit MM 74C74.
b) Insert on the matrix the integrated circuits MM 74C175 (quadruple rockers D synchronous), MM 74C86 (quadruple Ou-exclusif), MM 74C08 (quadruple AND) and carry out the connections indicated to the figure 10-a.
The electric diagram of the circuit carried out is given to the figure 10-b. Entries CLOCK and CLEAR are common to the four rockers, and the four exits Q1, Q2, Q3 and Q4 order respectively the LED L0, L1, L2 and L3.
5. 2. - OPERATIONAL TESTS
a) Put SW0 on position 0 and energize the digilab: the four LED L0, L1, L2 and L3 are extinct, entry CLEAR being active.
b) Put SW0 on position 1 : entry CLEAR is from now on inactive and the four LED remain extinct. Let us indicate this state of the exits by state 0.
State 0 : Extinct L3 (Q4 on the level L)
Extinct L2 (Q3 on the level L)
Extinct L1 (Q2 on the level L)
Extinct L0 (Q1 on the level L)
c) Support now on P0 : L0 ignites while the other LED remain extinct. Let us indicate this state by state 1.
State 1 : Extinct L3 (Q4 on the level L)
Extinct L2 (Q3 on the level L)
Extinct L1 (Q2 on the level L)
Lit L0 (Q1 on the level H)
d) Continue to actuate P0 and note the states of the exits after each pressure on P0 : you obtain the table of figure 11. (Return to the Play of electronics)
The chronogram of figure 12 makes it possible to know the levels present on the exits Q1, Q2, Q3 and Q4 according to the pulse repetition frequency applied to the entry of clock.
You note that there are 16 states different noted from 0 to 15.
After the sixteenth clock pulse the circuit returns in an initial state 0, its capacity of counting being exceeded.
The meter carried out thus has a capacity of 15 and one module of 16.
e) Put not under tension the digilab.
The meter carried out has the advantage of being synchronous.
Indeed, the four rockers which make it up are ordered by the same clock signal; they thus commutate at the same moment.
This cannot be checked in practice because it is necessary to have special measuring apparatus.
Indeed, the switching time of a rocker is about ten-millionth of second.
The table of figure 11 (see above) gives interesting indications to use the meter.
It is enough to observe the state of the four LED to know the pulse repetition frequency arrived on the entry to the meter.
If for example the LED L3 and L2 are lit and that the LED L1 and L0 are extinct, one immediately sees in the table that twelve impulses arrived on entry CLOCK.
The examined meter gives the result of counting in binary code (HHLL = 11002 = 12 into decimal).
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