Capítulo 3. Diseño de las pruebas y análisis de los resultados
3.7 Conclusiones de las pruebas
dhurjati sinha the number in 7-segment display keeps
changing on flipping switch S1 from ‘run’
to ‘stop’ condition slowly decays before stopping with a random number display.
To play this game, one has to obtain three identical numbers in displays DIS1 through DIS3. The contestant would score 1 (one) point if he manages to get a final display of ‘000’, 2 points for getting
‘111’ display, 3 points for ‘222’,… and so on—up to ten points for ‘999’. He should try to score maximum possible points in fixed numbers of attempts (say, 20 to 25 attempts).
Apart from using this circuit as a game for entertainment, one can use it as random number generator for any other application as well. The decay time with the given component values is around 15 seconds before the display could stop at a final random number.
The circuit comprises clock oscillator built around NE555 timer IC4, three-stage clock pulse counter built using three CD4033 ICs (IC1 to IC3), and three 7-seg-ment LED displays (DIS1 to DIS3).
In clock oscillator circuit, NE555 timer IC4 is used in a similar way as a free-running astable multivibrator, the only difference being the additional ca-pacitor C1 introduced between pin No. 7 of IC4 and junction of resistors R22 and R24. When toggle switch S1 is in ‘run’ po-sition, both terminals of capacitor C1 are shorted by switch S1 and timer IC4 works as a free-running astable multivibrator.
The operating frequency is in the vicin-ity of 35 kHz, determined by the value of timing components.
When toggle switch S1 is flipped from ‘run’ to ‘stop’ position, capacitor C1 is introduced in the discharge path of pin No. 7 of IC4 and junction of re-sistors R22 and R24. At the same time, capacitor C4 comes in parallel with
timing capacitor C3 to change the op-erating frequency of the astable from around 35 kHz to around 65 Hz. Now capacitor C1 slowly starts charging as it is connected in the discharge path of the timing capacitors C3 and C4.
The clock frequency of IC4 gradually reduces and after 15 seconds, when capacitor C1 is sufficiently charged, the oscillating frequency gradually drops and finally it stops oscillating.
Thus, pin 3 of IC4 becomes low.
Second part of the circuit comprises three cascaded ICs, IC1 through IC3 (CD4033 decade upcounter cum 7-seg-ment decoder). In conjunction with three 7-segment displays (DIS1 to DIS3), these form a 3-digit clock counter. The clock counting speed is dependant upon the clock pulse frequency of IC4. It is con-nected to clock input pin 1 of IC1 while chip enable pin 2 of IC1 to IC3 are held low. Thus all clock counter ICs advance
by 1 for every positive clock transition.
Reset pin 15 of all counter ICs is held low through resistor R25. Thus reset facility is not used in this circuit.
Due to persistence of vision, one can-not distinguish 0-9 counting in DIS1 to DIS3 when the clock frequency is high.
All 7-segment displays appear to show digit 8, while the red LED1 remains lit continuously, indicating clock counter is in running condition.
On sliding toggle switch S1 from
‘run’ to ‘stop’ position, the counting speed of individual digits falls immedi-ately due to the clock frequency chang-ing to around 65 Hz. Now, the countchang-ing speed will be 65 Hz for DIS3, 6.5 Hz for DIS2, and 0.6 Hz for DIS1. This speed of individual digit counting slowly decays, until the counter stops and LED1 stops blinking, and the final count (random numbers) are displayed in DIS1, DIS2, and DIS3.
T
his circuit is able to handle nine independent telephones (using a single telephone line pair) located at nine different locations, say, up to adistance of 100m from each other, for re-ceiving and making outgoing calls, while maintaining conversation secrecy. This circuit is useful when a single telephone
line is to be shared by more members re-siding in different rooms/apartments.
Normally, if one connects nine phones in parallel, ring signals are heard in all
the nine telephones (it is also possible that the phones will not work due to higher load), and out of nine persons eight will find that the call is not for them. Further, one can overhear others’ conversation, which is not desirable. To overcome these problems, the circuit given here proves beneficial, as the ring is heard only in the desired extension, say, extension number
‘1’.
For making use of this facility, the calling subscriber is required to ini-tially dial the normal phone number of the called subscriber. When the call is established, no ring-back tone is heard by the calling party. The call-ing subscriber has then to press the asterik (*) button on the telephone to activate the tone mode (if the phone normally works in dial mode) and dial
extension number, say, ‘1’, within 10 sec-onds. (In case the calling subscriber fails to dial the required extension number within 10 seconds, the line will be discon-nected automatically.) Also, if the dialed extension phone is not lifted within 10 seconds, the ring-back tone will cease.
The ring signal on the main phone line is detected by opto-coupler MCT-2E (IC1), which in turn activates the 10-second ‘on timer’, formed by IC2 (555), and energises relay RL10 (6V, 100-ohm, 2 C/O). One of the ‘N/O’ contacts of the relay has been used to connect +6V rail to the processing circuitry and the other has been used to provide 220-ohm loop re-sistance to de-energise the ringer relay in telephone exchange, to cut off the ring.
When the caller dials the extension number (say, ‘1’) in tone mode, tone
re-ceiver CM8870 (IC3) outputs code ‘0001’, which is fed to the 4-bit BCD-to-10 line decimal decoder IC4 (CD4028). The output of IC4 at its output pin 14 (Q1) goes high and switches on the SCR (TH-1) and associated relay RL1.
Relay RL1, in turn, connects, via its N/O contacts, the 50Hz extension ring signal, derived from the 230V AC mains, to the line of telephone ‘1’. This ring signal is available to tele-phone ‘1’ only, because half of the signal is blocked by diode D1 and DIAC1 (which do not conduct below 35 volts).
As soon as phone ‘1’ is lifted, the ring current in-creases and voltage drop across R28 (220-ohm, 1/2W resistor) increases and oper-ates opto-coupler IC5 (MCT-2E). This in turn resets timer IC2 causing:
(a) interruption of the power supply for processing circuitry as well as the ring signal relays RL1 through RL9, and
(b) removal of loop re-sistance R16, via the second contact of relay RL10.
As a result, the telephone line voltage shoots up to 48V, DIAC1 and diode D1 con-nected in series with phone 1 conduct within a few mil-liseconds, and phone 1 comes into operation. The telephone exchange does not interpret this as break in off-hook condition, since some delay margin is set at exchange.
When phone ‘1’ is busy, the other eight phones will not work, since line voltage will again drop to 10V and the other diacs will not conduct. Thus conver-sation secrecy will be maintained.
The other extensions also work in a similar manner when another extension number is dialed and its corresponding relay energises to extend the 50Hz ring to another extension.
The 24V, 50Hz ring signal derived from transformer X1 is sufficient for working with phones of Beetel and ITI make, but for Pretel and some other makes, it may be necessary to increase the ring voltage to about 30 volts or even higher.
TAble I
Appliance LDR2 LDR3 LDR4 LDR5 no.
1 - * * *
2 * - * *
3 - - * *
4 * * - *
5 - * - *
6 * - - *
7 - - - *
8 * * *
-9 - * *
-10 * - *
-11 - - *
-12 * * -
-13 - * -
-14 * - -
-15 - - -
-- Blocked hole corresponding to selected binary address.
* Punched holes corresponding to LDR posi-tion on card
priyank mudgal
ElEctronic card lock SyStEm
T
his circuit of electronic card lock system is much simpler and cheaper than other similar circuits that have appeared in earlier issues of EFY.The circuit is configured around an addressable 1 of 16 demultiplexer CD4514B (IC1). Any number in binary form, when available at input pins 2,
3, 21, and 22 (address pins A0 through A3), makes corresponding output go logic high, thus turning on the appliance through relay contacts. Up to 15 appli-ances can be switched on/off (one at a time). Output Q0 (pin 11) can be used for visual indication, to show that circuit is active.
A 40W bulb illuminates LDR1
t o L D R 5 constantly.
This pulls down bases of transis-t o r s T 1 through T5 to ground.
LDR1 en-sures that card is prop-erly inserted into the card slot.
When the card is correctly inserted, it covers the hole/open-ing for LDR1 and thus blocks the light from falling on LDR1. As a
result, transistor T1 conducts and ex-tends positive supply to the collectors of transistors T2 through T5. Then, depend-ing upon the holes blocked/punched in the inserted card, any combination of emitters of transistors T2 through T5 turns logic ‘high’ (transistors’ output corresponding to blocked LDRs only goes
‘high’). These outputs connected to address input pins A0 through A3 of IC1
switch on the corresponding appliance (one out of 15).
The card used should be of opaque plastic. It should be able to withstand some heat from the bulb, even though the appliance remains ‘on’ only for the period for which the card is in the slot.
The card has a triangular notch that shows correct orientation/direction of insertion of card and prevents false op-eration. LDRs can be placed in a line, or randomly, to increase security.
The order in which holes should be punched for each appliance is given in Table I. Two illustrations, one each for card-2 and card-5, are shown in the ac-companying figures. An elevation and plan/top view of the gadget is also shown in the figures.
dr. alika khare