2. REVISIÓN BIBLIOGRÁFICA
2.3. PRODUCCIÓN FAMILIAR
2.3.2. Ciclo de vida familiar; género y la toma de decisiones
A.U. AHMED
The circuit becomes operational only when switch Sl is in position 3. Precisely at the alarm set time, a mo- mentary high state of alarm output trig- gers IC1, which is wired as a monostable multivibrator. IC1’s output pulse is used to set the internal ‘sleep counter’ of the clock IC by providing necessary high state to the ‘sleep dis- play input’ and ‘fast set input’ simulta- neously. The pulse length, and hence the sleep counter setting, is adjustable by potentiometer VR2.
The resulting high sleep output is used to drive the relay through tran- sistors T2 and T3. Sleep display input
is also provided with the necessary high state to display the countdown process. At the end of the duration, IC2, triggered by the negative going pulse edge, triggers the tone genera- tor IC 555 for approximately one minute. However, an alarm reset push- button switch is also provided. Manual on and off switches are provided to facilitate manual operation. With switch Sl in position 1, the clock func- tions as usual.
To calibrate VR1 and VR2, keep switch Sl in position 2. In this mode, the circuit can be test-operated with- out disturbing the relay output. Now,
W
ith the addition of the circuit described here, your digital clock, built around IC MM5387, can be used to automatically switch on an electrical appliance at the alarm set time. It can also be used to switch it off after a certain time duration, ad- justable between 1 and 59 minutes. The circuit also features display of the countdown (in minutes) to the comple- tion of the process, which is an- nounced by a self-resetting audible alarm. So, it can prove very useful for the automatic operation of a vari- ety of electrical appliances, such as heater, geyser, TV, VCR, etc.One set of contacts is used for indica- tion and another for heater supply. When relay is de-energised, the red LED indicates that there is no water inside the container.
The circuit can be built on a small general-purpose PCB, housed in a small metal box, fixed very close to the equip- ment.
keep VR2 at its zero-resistance position. Adjust VR1 and press the manual on switch to get the sleep counter setting displayed. Then press the manual off switch briefly to try again. Achieve the required maximum setting of 59 minutes by trial and er-
ror. Similarly, keeping VR2 at its maxi- mum-resistance position, adjust VR4 for a setting of one minute. VR2’s dial may be marked accordingly. However, while setting the timer for real operation, it is advisable to cross- check VR2 dial-setting by operating
manual on/off switches in the test mode.
The relay output can drive low- power loads like TV and VCR directly. However, the optional circuit to drive loads with higher power rating is also given.
S
uppose you are in the bathroom or enjoying a TV program while your telephone is ringing. Someone is call- ing you on your phone. This is a very irritating situation. Perhaps you lift the telephone handset off the cradle and put it on the table to avoid this kind of situation. But there is a chance you may forget to place the handset back on the cradle. This simple circuit solves this problem.Connect this gadget to your tele- phone line. Press a switch whenever you want to disconnect your line. The telephone will get reconnected after a preset time, set by switch S1. Any- body trying to call you during this period will get a busy tone in his tele- phone.
The basic idea of this circuit is that it puts a resistive load equal to that of
your telephone set in the telephone line when you press switch Sl. The load gets disconnected after a preset time. The load forces the telephone exchange to think that the line is busy. So, any- body trying to get your number will receive a busy tone. The time period can be adjusted according to one’s choice.
The heart of the circuit is a 555 IC, which is wired in one-shot monostable on-timer configuration. On pressing switch S3, the IC gets power through the switch. At the same time, a nega- tive-going pulse is applied to the trig- ger pin of 555 through another part of switch S3. So, the timer starts work- ing, making the output pin high. As a result, relay RL1 energises.
On energising relay RL1, the cir- cuit gets its power through one of its
contact points. So, releasing switch S3 will not disconnect circuit from the sup- ply. Another contact point of the relay is used to apply a resistive load on the telephone line. A bridge rectifier is used to avoid the problem of polarity. The LED should glow, indicating that the silencer is working. The value of Rl may be changed to suit different tele- phone lines.
The time interval is set by switch S1 to 5, 10, 20 or 40 minutes. After this time, the line will be normal. Switch S2 is used to reset the circuit. After the time interval set, the circuit will get disconnected from the supply, causing no power consumption. A 9V battery may be used to power the circuit.
The circuit can be housed in a small box. Use miniature relay to save space. Transistor Tl needs a good heatsink.