Assembly
and control of operation of diodes LED |
Marking of the elements |
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Created it, 06/10/19
Update it, 06/10/20
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3. - CHECKING OF THE ASSEMBLY
You now will carry out a series of controls allowing you to check the exactitude of the assembly carried out until now. You will be able to thus proceed in full safety to the exercises which will follow.
3. 1. - CONTROL HORS-TENSION
Lay out your controller out of ohmmeter on the gauge W x 1 000. Put the test probes in contact with the two crocodile clips at the ends of flexible wire red and black of food.
The apparatus must indicate an infinite value.
If the value of measured resistance is null (switches on full scale), that indicates the presence of a short-circuit.
In this possibility, you will have to reverify all the weldings carried out attentively, to locate the place of the undesirable contact, then, to eliminate the short-circuit by using if necessary the soldering iron and the braid to be unsoldered :
by keeping one of the test probes in contact with the crocodile clip of the red
flex-wire, touch with the other point one then the other of the two contacts
located by the sign (+) as illustrated in
figure 20.
In both cases, the controller must indicate a null resistance: if resistance proves to be infinite (the needle remains on the left), check the welding of the pins of the two connectors and that of the red flex-wire on the copper tape + B.
connect one of the two test probes to the crocodile clip of the black flex-wire
and put the other in contact with each of the two contacts located by the sign -.
In both cases, the measured value must be null. If such is not the case, it is advisable to check the weldings of the pins of the two connectors and the black flex-wire on the copper tape - B.
3. 2. - CONTROL UNDERVOLTAGE
ensure you first of all of the absence of any piece of metal under the printed
circuit, this one being able to cause an accidental short-circuit.
if the blades of the pile are not accessible, remove the band of guarantee out
of paper.
connect the grip of the black wire of food to the blade (-)
of the pile (longest) and red wire with the blade grips it (+).
prepare the controller for measurement of them VCC
(continuous tensions), gauges 10 and, by
respecting the polarities of the controller, put the test probes in contact with
the two pins “+” and “-”
like clearly illustrated in figure 21.
The apparatus must indicate a tension ranging between 4,4 and 4,8 V.
You
must also find the same tension present on the two other contacts “+”
and “-”.
If the measured tension is lower (see null) on the two points of measurement, disconnects the pile and checks the tension between the two blades “+” and “-”. It must lie between 4,4 and 4,8 V.
After this checking, if the pile delivers the normal tension one will direct research towards the presence of a cold welding which it will be advisable to remake on the pins “+” and “-” one or other connector.
by keeping the test probe of the controller in contact with the grip of the
black flex-wire, test with the test probe of the positive pole, one after the
other, the lower limits (by looking at the printed circuit at the place) of
eight resistances of 220
W as
illustrated in figure 22.
On each of eight resistances, you must find the tension of the pile.
In the contrary case, it is advisable to check with the ohmmeter the value of the resistance on which the tension is not correct as well as the weldings on its terminals.
Lastly, check also the continuity of the track connecting resistance in question to the copper band + B of the food while serving to you as the ohmmeter.
In general, to check with certainty of the continuity of the tracks of a printed circuit and to make sure that no undesirable contact remains between the tracks or pastilles, it is enough to observe by transparency the printed circuit on the side of the tracks in illuminant the other side using a lamp what is not possible in certain cases, serigraphy having returned the opaque chart. We advise you however to observe the chart side circuit for want of anything better.
4. - ASSEMBLY
AND CONTROL OF OPERATION OF DIODES LED
You now will set up diodes LED and will take some measurements on these diodes.
The LED are diodes emitting of the light when they are polarized in the direction passing or direct (the anode must be positive compared to cathode). A complete and detailed examination of the diode will be in a lesson entitled Technologie 1.
On the simulator, diodes LED are used like level gauges logical. Ordered by a circuit of adaptation, they make it possible to distinguish one from the two binary states (either high level: presence of tension, enlightened LED corresponding at the binary state 1, bottom grade : absence of tension, extinct LED = binary state 0).
Before carrying out the assembly of the LED, it is wise to check them : for that, it is enough to put the controller on the position ohmmeter (W x 10 gauges). Place the positive test probe of the ohmmeter on the anode, the other on cathode : the LED must then ignite (figure 23-a), the needle of the galvanometer must indicate a value of resistance ranging between 300 and 600 W.
It should be remembered that on a controller of the current type, in position ohmmeter, the positive polarity of the pile used for this measurement appears on the terminal called “commun run”.
By reversing the polarities at the boundaries of diode LED, you note that it does not ignite and that the controller indicates an infinite resistance (figure 23-b).
It is not possible to carry out this test with a digital controller because the current traversing the circuit of the ohmmeter would not be sufficient to light the LED.
After checking of the correct operation of eight diodes LED, you can carry out their assembly :
take a diode LED and introduce it with the site envisaged on the printed circuit
and located by the L0 initials by deferring you to the figure 24-a for a correct
connection of its two terminals.
If the diodes which you have in your possession have on their connections a shoulder of stop, they will be automatically positioned with the correct distance of approximately 3 mm of the printed circuit, as illustrated in the figure 24-b. It is thus sufficient to maintain them in place with a finger, then to turn over the circuit and to carry out the welding of the two terminals to the corresponding copper pastilles.
However, certain LED can be deprived of shoulder on their connections.
In this case, maintain those to 3 mm above the circuit, then, side coppers, draw aside their connections slightly. Thus, you can turn over the circuit, the diode remains in place time to carry out its weldings.
After this operation, you can cut the part in excess of connections of the LED.
Before passing to the assembly the following ones, carry out the control of the first :
feed the circuit by connecting the crocodile clip of the red cord on the
terminal “+” of the pile and the grip of
the black cord on the terminal “-”.
position the controller for the measurement of D.C. current on the gauge higher
than 25 mA at the end of the scale, pose the
black test probe on the terminal “-”
pile and the red test probe in contact with the cathode of diode LED, like
illustrated figure 25. This established contact, the LED ignites and the
galvanometer must indicate a current ranging between 10
and 15 mA.
If the LED does not ignite and that the controller does not announce any passage of current, you must ensure yourselves above all to have correctly identified the terminals of anode and cathode of diode LED. If you cabled it with back, it is necessary to unsolder it by means of the suitable braid and to correctly replace it while paying a greater attention with the indications like with the quoted figures.
On the other hand, if the LED still does not ignite and that the controller indicates a current ranging between 19 and 25 mA, it is probable that the red test probe was put by error in contact with the anode instead of cathode.
Lastly, despite everything these controls, if you do not obtain the illumination of the LED, ensure you again of the presence of a tension on the lower limit of resistance equal to that of the pile (see control undervoltage, paragraph 3.2). This tension being checked, one can suppose a failure of the diode.
Unsolder the latter and control it with the ohmmeter and possibly replace it by another.
The control of operation of the diode in place being conclusive, you can carry out the assembly of the seven other LED (figure 26) :
while following the instructions provided previously,
weld the seven remaining LED with the sites envisaged onto the printed circuit
and located by L1, L2, L3, L4, L5, L6 and L7 while giving all the attention
necessary for the identification of cathodes. Lastly, check the operation of
each one of them as well as the current absorptive while proceeding in the same
way as for the LED L0.
With the control of all the LED the first practical realization finishes.
In the next one, you will continue the assembly of the simulator by carrying out the control circuit to transistor of each LED and you will carry out the first tests with the logical integrated circuits.
At the beginning of this lesson, the relation between the theory and the practice are not obvious. However, progressively with the progression, the subjects will be juxtaposed and connected chapters in chapters. Your examination will have to progress in the same order.
You will find also technical information and notes there on the components, the integrated circuits, etc…
To finish this lesson, chapter 5 recapitulates the principal systems of marking of the components.
5. - MARKING
OF THE ELEMENTS
The location of the value of resistances and the condensers can be carried out several manners according to manufacturers :
1 - Resistance marked “in light”.
Sometimes, this value appears in a clear way, just as the tolerance, without the recourse to any particular code ; but that is very rare.
Often, the W symbol is omitted and one finds only at side or in lower part of the number, the prefixes K or M for the great values. For example : 1 K - 270 - 1M08 - 9k00 means 1 kW - 270 W - 1,08 MW and 9 kW.
Frequently, the W symbol is replaced by the letter R for the values lower than 1 kW. If this one is placed before the number, that indicates a comma preceded by one zero. For example following indications : 4 R 5 - 10 R 0 - 900 R - R 30 indicate respective values of 4,5 W - 10 W - 900 W and 0,3 W.
2 - Resistance marked by the code to 4 colors and you point out that we had
already spoken in the electronic lessons fundamental ones and defer we it here
(figure 11). It is used the most. The table below points out it to you.
3 - Resistance marked by the code to 5 colors and we defer the same table
already explained in the lessons of electronic fundamental (figure 12).
It is about the same principle as for the preceding code. See the table below. Here an example of reading with this code :
Bench (9) Black (0) Black (0) Yellow (x 10 000) Chestnut (1%) = 9 MW 1%
Orange (3) White (9) Red (2) However (x 0,1) Red (2%) = 390 W 2%
Yellow (4) White (9) White (9) Black (x 1) However (5%) = 499 W 5%
4 - Condenser marked “in light”.
The value of the capacity, the tension of work and the tolerance are expressed clearly on the body of the condenser. But considerable manufacturers eliminate from marking the measuring units and the zeros which precede the comma.
If the number which expresses the capacity starts with a figure different from zero, the unit is the picofarad. If this number is followed by small letter “n” or “k”, it is about nanofarad.
If the number indicating the capacity begins with one zero, a comma or a point, the unit is the microfarad. The point preceding the first figure indicates an imaginary comma preceded by one zero.
Example :
1000 10 % 630 = 1000 pF 10 % 630 V
1 n 0 = 1 nF
470 k = 470 pF 10 %
.01 = 0,01 µF = 10 nF
100 M = 100 pF 20 %
The first capital letter which follows the number indicates the tolerance and the second, if it exists, is the temperature coefficient. The most current tolerances on the ceramic condensers are 2,5 % (H), 5 % (J), 10 % (K), 15 % (L), et 20 % (M).
For the condensers with polystyrene, one can find moreover, one coloured band indicating the tension according to the following correspondence : Blue = 25 V - Yellow = 63 V - Red = 160 V - Black = 630 V.
CAUTION
In certain cases, the number indicating the value of the capacity is written in code. It is then always about an integer of three digits from which the last (on the right) is different from zero. The two first are the first two significant figures and the third indicate the number of zeros to add to obtain the value of the capacity (in picofarad).
Example :
472 = 47 00 = 4 700 pF = 4,7 nF
101 = 10 0 = 100 pF = 0,1 nF
5 - Condenser marked by the code of the colors (figure 23).
This code is similar to that used for resistances. The table below enables you to make of it the reading of which we had already explained in the lessons of electronic fundamental.
6 - Location of the electrodes of an active element.
The location of the transistors can be made various manners: a point of color, a metal pin, a flat part, etc…
The integrated circuits are also located by one obviously located on the case.
For the components used in the practical assemblies, stitching will be always given to you.
We finish this first practice thus.
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