Created it, 06/10/19
Update it, 06/10/27
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4. - ASSEMBLY OF A DOUBLE GENERATOR OF CLOCK ON THE DIGILAB
You now will carry out on the printed circuit of the digilab the assembly of two independent oscillating circuits, which could be used as generators of clock signals to order later on the circuits tested on the matrix.
To carry out the assembly, you will use the support located by the symbol IC2 in which will be inserted the integrated circuit MM 74C14. The components to be welded are: six marked resistances R20, R21, R22, R23, R24, R25 and two condensers located by the symbols C1 and C2.
The procedure of assembly is as follows :
a) Disconnect the food and remove the connections of the group of connectors.
b) Dismount the plate of the printed circuit of its box so as to be able to easily carry out the weldings on the side coppers. For that, also unscrew the fastening screws of the metal front face to be able to remove the two cords of red and black food of the plate.
c) After you to be ensured of their value the ohmmeter, weld in the order onto the printed circuit, following resistances by respecting the instructions of wiring given in practice 1 (figure 11).
R20 of 12 KW 5 % (chestnut - red - orange - but)
R21 of 150 kW 5 % (chestnut - green - yellow - but)
R22 of 1,5 MW 5 % (chestnut - green - green - but)
R23 of 15 kW 5 % (chestnut - green - orange - but)
R24 of 150 kW 5% (chestnut - green - yellow - but)
R25 of 1,5 MW 5 % (chestnut - green - green - but)
d) Then weld onto the printed circuit the following condensers :
Electrolytique capacitor C1 with the tantalum of 0,33 µF - 10 V
Condensing C2 ceramic disc of 330 pF.
CAUTION : The C1 condenser must be assembled while respecting the polarities of its terminals. The positive terminal, located by the sign + must be inserted in the hole marked + on the printed circuit. For a correct identification of this condenser whose value can be also marked with the code of the colors, on this subject read the technical note deferred on the boards of material.
4. 1. - CONTROL NOT UNDER TENSION
You ensure initially that the assembly of the components on the printed circuit corresponds to that of figure 7. Prepare then the controller for the measurement of resistances on the gauge W x 1 000. Check that between the contact marked 1 Hz and the upper limit of R25 well than you find a value ranging between 1,3 and 1,7 MW. This checking is clearly illustrated by figure 8.
Continue then control not under tension by taking measurements between the points indicated in the table of figure 9.
| N° | CONNECTIONS TO CHECK A THE OHMMETER | VALUES TO BE OBTAINED |
| 1 |
Between contact 1 Hz and the upper limit of R25 |
1,3 to 1,7 MW |
| 2 |
Between contact 10 Hz and the upper limit of R24 |
130 to 170 kW |
| 3 |
Between contact 100 Hz and the upper limit of R23 |
13 to 17 kW |
| 4 |
Between contact 1 Khz and the upper limit of R22 |
1,3 to 1,7 MW |
| 5 |
Between contact 10 Khz and the upper limit of R21 |
130 to 170 kW |
| 6 |
Between contact 100 Khz and the upper limit of R20 |
10,5 to 13,5 kW |
| 7 |
Between contact COM1 and the terminal + of C1 |
0 |
| 8 |
Between contact COM2 and the right terminal of C2 |
0 |
If at the time of the one of these controls, the value of measured resistance is not within the limits indicated or is infinite, that means that resistance in question does not have the value envisaged or that there is a cut.
In this case, it is necessary to check resistance concerned, the continuity of the copper tracks and to ensure you of the quality of the weldings carried out.
4. 2. - OPERATIONAL TEST
a) Go up the printed circuit and the front face on the box.
b) Remove the integrated circuit MM 74C14 of the matrix and introduce it into support IC2 where it will remain permanently from now.
The electric diagram of the circuit carried out is shown figure 10. As you can see it, it consists of two oscillating circuits RC independent of which each one uses two reversers with rocker of Schmitt and is able to generate rectangular signals of three different frequencies.
The two circuits function in the following way:
by connecting using a piece of wire contact COM1
with one of the three marked contacts 1 Hz, 10
Hz, 100 Hz, you put thus in
circuit respectively R25, R24, or R23
and the first circuit oscillates by producing a rectangular signal of
corresponding frequency. This signal, after having crossed a second rocker of
Schmitt providing the function of “plug”
between the oscillating circuit itself and that to order, is available on the
contact marked CP1 of the group of
connectors.
the second oscillating circuit functions in the same
way : while connecting contact COM2
with one of the three contacts marked by 1 kHz,
10 kHz, 100 kHz,
you respectively insert in the circuit resistance R22,
R21, or R20. The signal having
the frequency indicated is available on the contact marked CP2
of the group of connectors.
To check the correct operation of the two circuits, proceed as follows:
a) Connect contact CP1 with the L1 contact of the group of connectors, then contact COM1 with that marked 1 Hz, as illustrated on figure 11.
b) Connect the food: the first oscillator generates a rectangular signal of frequency 1 Hz. Indeed, you note that the LED ignites 1 / 2 second then dies out one 1 / 2 second and so on. That corresponds well to a period of 1 second, therefore at a frequency of 1 Hz.
If the circuit does not function, attentively check the connections, the weldings and the components.
c) Disconnect the food and move the driver connecting contact COM1 with the contact marked 1 Hz so that contact COM1 is connected with contact 10 Hz.
d) Connect the food : the LED L1 flickers again, but at intervals much faster, approximately ten times a second.
e) Disconnect the food again and connect COM1 with contact 100 Hz.
f) Connect the food : the LED L1 ignites and remains lit. This should not be interpreted like a faulty operation of the circuit : indeed, the circuit generates a rectangular signal of frequency 100 Hz. The LED L1 ignites and dies out thus hundred times a second, and the eye is not able any more to appreciate the succession of lightings and extinctions.
However, you notice that the LED is less luminous than usually ; that indicates that actually it is not always lit and that it ignites and dies out in alternate cycles.
In the following test, relating to the second oscillator, since the frequencies of the generated signal are even higher, it will be practically impossible to make sure with certainty of the correct operation of the circuit.
Indeed, the LED L1 will present a practically normal luminosity. However, you will have the occasion to carry out a more precise control of the correct operation of the oscillators by using circuits of counting in the next practical one.
Pass now to the tests of the second oscillator.
g) Disconnect the food, remove the preceding connections and connect contact CP2 with the L1 contact of the group of connectors, as well as contact COM2 with contact 1 kHz.
h) Connect the food : the LED L1 ignites and is slightly less less luminous than the normal. That indicates that the oscillator functions, generating a rectangular signal of frequency 1 kHz.
i) Test then the operation of the circuit at the frequencies of 10 kHz and 100 kHz with the adapted connections, i.e. by connecting COM2 initially to contact 10 kHz then with contact 100 kHz and observe each time the LED L1. You point out that each time you move the connections, it is necessary to disconnect the food.
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