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Project Tutorial:    "Electronic House"

 by Ranjith K H

 

            This is a 'do-it-yourself' tutorial of "Automated house". Author explains some methods to make handling of home equipments easy and secure. Auto alarm, scheduled tasking, remote operated equipments, touch alarms and water level controller.


Abstract
: To develop security system for houses and to save electric  power. 

Scope : This project proposes the development of security system for form houses and residential houses. 

In an extremely mechanized word such as today’s it is necessary to make our life better, convertible and economical. This is the purpose for which the Electronic house is developed.

              Electronic house consists of six major units. They are

  1. Remote operated gate control
  2. Automatic gate light, call bell system
  3. Auto adjustable timer unit
  4. Remote operated electrical equipments
  5. Touch sensitive burglar alarm for internal security
  6. Water level indicator and controller in a tank

Click here to view photographs of demo model.  

Remote operated gate control

             This unit is responsible for opening and closing the gates at the pressing of a button on remote transmitter. 

Automatic gate light, call bell system

              During day time, this unit generates a musical alarm, when anyone entering the compound of the house. During night time, at the entry of any person through the gate, the compound lights are switched ON together with musical bell.

 Auto adjustable timer unit

              This unit can be used to operate an electrical equipment for a fixed period of time. The circuit can be used for street lightning, billboard illumination and water supply to the garden where pump can be set to switch ON at one time and switch OFF at another tome.

 Remote operated electrical equipments

               This unit replaces the conventional switchboards. Fans, lights and other equipments can be operated and controlled using remote controlled unit.

 Touch sensitive burglar alarm for internal security

                This simple circuit when connected to a metal locker or cupboard generates an alarm when touched by an undesired entity.

 Water level indicator and controller

                This indicates the water level in the water tank at four steps F, H, L, E, i.e., Full, Half, Low, Empty. When the tank is empty the unit automatically switches ON the water pump and switches OFF when the water level reaches to full.

              This multipurpose electronic house has been successful in gaining public attention. It has won many prizes at state and district level competition.

 Prizes :

  •  First place in model display competition in CORONA-2004 a state level inter collegiate and cultural fest held on January 14th and 15th of 2004 at Sri Bhuvanendra College, Karkala.

  •   First place in the intercollegiate model display competition during ELECTROFEST-2004 held on 16th and 17th January 2004 at Mangalore University.

  •   First in model display competition in IMPRINTS-2003 held on 27th and 28th of November 2003 at St Aloysius College, Mangalore.

 Conclusion :

            This electronic circuit explained above is only a model, and incorporated in a cardboard model house. These circuits can be incorporated, and realized in a large scale.  

Adjustable timer unit 

            There is a variety of outdoor light controllers available. Some switch lights ON at the fall of dusk and OFF at the break of dawn. Others switch lights ON at the end of dusk and OFF after few hours. But for domestic use, where we require light in the early morning also, these do not serve the purpose. The circuit described here solves this problem.

 It offers the following features:

  1. It switches ON lights at about 6.00 PM and switches OFF at about 11.00 PM. Again it switches ON lights at about 4.30 AM and switches OFF about 6.00 AM. We can change this time by changing simple components.
  2. There are separate ON and OFF switches for easy operation of the system.
  3. It use LED indicators to detect deferent conditions of the circuit.
  4. Preset control to set the trigger time.

 The circuit comprises five sections.

  

 

    1. Triggering

            This section is used to trigger the circuit at the fall of dusk. It is configured around IC 1, which is working in the monostable mode. A variable voltage is fed to trigger pin 2 of IC 1 via LDR and VR 1. In the monostable mode of operation, the output of IC 1 stays high as long as its trigger input stays bellow 1/3 Vcc.

         At night, the resistance of LDR is high, so the voltage at pin 2 is at a low level and hence the output of IC 1 goes high at night. The output condition of IC 1 can be detected from LED 1. the output of IC 1 gives power supply to the next stage.

2.    Resetting

            The next section is used to reset two 4017 decade counter ICs used in the counter section. This is also based on a 555 timer [IC 2]. Its trigger pin 2 is connected to capacitor C3 and resistor R4. In the absence of supply, there is no voltage across capacitor is bellow 1/3 Vcc and its output goes to a high state. The voltage across capacitor C3 increases, so that the voltage at pin 2 crosses 1/3 Vcc. The time period for which the output stays in the high state depends upon resistor R5 and capacitor C4 and is given by the relationship 1.1*R5*C4.

            The output of IC 2 is given to the reset pin 15 of decade counter IC 3 and IC 4. These ICs are reset when IC 2 is triggered, and as long as the output of IC 3 is in the high state, the counters sty in the reset position. 

     3. Oscillator

            This section is used to produce a square wave output. It is based on IC 5 an NE 555. Its output frequency depends upon resistors R6 and R7 and capacitor C5 and is calculated by the equation

                                            1.443/( (R7+2R6)C5)

The output frequency is fed to the counter section. 

     4. Counting

            The counter section is used to count the output frequency from the oscillating section. It uses two CMOS CD4017 ICs. The frequency from oscillating section, IC 5, is fed to the input pin of IC 3. IC 3 works as frequency divider and its output is fed to the input pin of IC 4.

            The four outputs of IC 4 are combined by using diodes D1 through D4. This combined output is given to the last section. If any of the output is high, then the load is ON state. The condition of this combined output is detected by LED 2.

      5. Output 

            The output section is used to switch the relay ON and OFF. It is based on BEL 187 transistor. The relay is connected at the collector of transistor. Diode D5 is connected to protect transistor. The output from the counting section is fed to the base of transistor through resistor R3. If the output from counting section is high, it biases the transistor and thus the relay is activated.

 Working:

            At the fall of dusk, the resistance of LDR increases, so a large voltage is dropped across it, resulting in a decrease in the voltage at pin2.

            When the voltage at pin 2 drops below 1/3 Vcc, IC 1 is triggered and stays in the high state still morning. Since the output of IC 1 is high, the next three states get power supply.

            When C3 is fully charged, IC 2 is triggered and reset pins of IC 3 and IC 4 both get a positive value. Therefore, the first outputs of both ICs are high. This condition changes when the voltage across capacitor C4 crosses 2/3 Vcc, because then the output of IC 2 goes to a low  state and the reset pins of IC 3 and IC 4 get a negative pulse each. In this condition IC 3 gets ready to accept pulses from the oscillating section and its outputs are changed.

            For each set of ten pulses from IC 5 the outputs of IC 4 are changed one by one. The output time period of oscillating section is about 540.5 seconds, i.e. about nine minutes. Since IC 3 divides the output frequency from IC 5. IC 4 gets a time period 9*10=90 minutes, i.e. one and half hours. So, the outputs of IC 4 are changed every one and half hour’s duration.

            When the controller is switched ON, the output Q0 at pin 3 of IC 4 is high and it turns on the load for first one and a half hour. Then, the next output Q1 at pin 2 is high, which switches ON the load for the second one and a half hour. Next, output Q2 at pin 4 goes high, which switches ON the load for the same period again.

            When the output Q3 at pin 7 is high it switches of the relay as pin 7 has no connection. Then, the output of IC 6 changes to Q4, Q5, Q6 for each one and a half hour, and when it reaches Q7(i.e. pin 6) the load is again switched on. After one and a half hour, the output is changed to Q8 (pin 9). Since pin 9 of IC 6 has no connection, it again switches OFF the relay.

            At the break of dawn, the resistance of LDR decreases, and the trigger pin of IC 1 gets a positive voltage greater than ½ Vcc, so that its output goes low which, in turn cuts off power supply to the next three stages.

 Automatic gate light, Call bell system

             This circuit may used to automatically switch ON a light at the entrance gate to premises, at night, by sensing the presence of a person. In addition, it sounds a musical bell to signify the presence of a person. The lamp is switched ON only for a short interval to save electricity.

            This circuit has two stages: a transmitting unit and a sensing unit. This transmitting unit consisting of a point bulb and lens to focus the light. The transmitting unit emits a beam of light. This beam falls on LDR1. LDR1 offers a very low resistance. Voltage at pin 2 of IC 1 and IC 2 is more than 1/3 Vcc, so that its output goes low.

            When any person tries to enter the gate, the light beam falling on the LDR1 is momentarily interrupted. As a result IC 1, configured as monostable flip-flop, gets a trigger pulse at its trigger input 2. Its out goes high for a predetermined time period. The period can be adjusted by varying the value of resister R1 or capacitor C1 as T=1.1*R1*C1 sec.

            Output pulse from IC 1 forward biases the transistor T1. As a result the musical bell is switched ON. The musical bell is built around IC 2(UM 66). The output from IC 2 is amplified by transistor T2 to drive an 8-ohm, 500mW-load speaker. IC 2 is also gets trigger pulse at its trigger input when IC 1 gets trigger at its trigger input because trigger input pin 2 of IC 1 and IC 2 are shorted. Therefore its out goes high for a predetermined time period. The period can be adjusted by varying the value of resister R2 or capacitor C2 as T=1.1*R2*C2 sec. Output pulse from IC 2 forward biases transistor T3 and relay R1 is energized, but the bulb is switched ON only at night.

            An LDR based circuit is used to switch ON the bulb at night only. The bulb is switched ON when relay R1 and R2 are energized. Relay R1 and R2 are connected in series with bulbs to the power supply. Two relays are like two switches of the bulb.

             During day time LDR offers a very low resistance, and thus the voltage pin 2 of IC 4 is more than 1/3 Vcc, so that its output goes low and the relay R2 is de-energized. These results in opening of power supply contact to the bulbs and thus switching OFF the bulbs. During the night time the dark resistance of LDR is very high, and thus the voltage at pin 2 of IC 4 is less than 1/3 Vcc, so that its output goes low and the relay RL 2 is de-energized. These results in shorting of power supply contact to the bulbs and thus switches ON the bulbs.

 

Water level indicator and controller

                Generally overhead tanks are filled with water by operating a pump. We have no control over the level to which it may be filled. It may cause overflow or water level may remain too low when we switch OFF the pump motor. Manual operation of the motor pump starter is thus not advisable. Present circuit may be added to the existing manual starter of the pump motor so that it may be operated automatically.

            Four sensor probes made up of brass or stainless steel stiff wires or rods may be hung firmly in the tank. This indicates the water level in the water tank at four steps F, H, L, E i.e., Full, Half, Low, Empty. When there is no water in the water tank the circuit automatically switches ON the pump and switches OFF when the water level comes to Full.

            Probes marked E and L are hung with their bottoms near the bottom level of the tank at which we wish to start the pump. The probe F is hung with its bottom end in between those probes E and F. It is used for indication of the middle level.

            Sensor H, L, F are connected with resistors R1, R2, and R3, where as probe E is directly connected to ground. Resistors R1, R2, R3 are connected to 12V supply through resistors R4, R5 and R6 respectively. 

Working:  

            When the water level in the tank is below probes E and L, output of gate N9 is logic low and output of gate N12 is latched to logic high level. Simultaneously output of gate N11 goes logic low and is inverted by inverter. Now the output of gate N10 becomes logical high, and thus the transistor is forward biased to ON state and the relay is energized. These results in shorting of power supply contact to the pump and thus switching ON the pump motor.

            As the water starts filling in the tank and ultimately touches probe F, the output of gate N11 goes high and is inverted by inverter. Now the output of gate N10 becomes logical low, and thus the transistor is reverse biased to OFF state and the relay is de-energized. These results in opening of power supply contact to the pump and thus switching OFF the pump motor.

            Water level states are displayed using IC 5 and IC 6 in conjunction with 7-segment display. The display indicates F for Full, H for Half, L for Low and E for Empty level condition. 

 Remote control unit

             This unit replaces the conventional switch boards. Fans, light and other equipments can be operated and controlled using remote control unit. Also, this unit can be used for opening and closing the gates at the pressing of a button on the remote control.

            This circuit has two stages: a transmitting unit and a receiver unit. The transmitting unit consisting of an infrared LED and its associated circuitry. The receiving unit consists of a sensor and its associated circuitry. The IR LED emit infrared light switch is put on in the transmitting unit. To generate IR signal 555 IC based astable multivibrator is used. Infrared LED is driven through transistor BC 177.

            In receiver section, the first part is a sensor, which detects IR pulses transmitted by IR-LED. When any key on the remote control handset is depressed, the output of IR sensor momentarily transits through low state. As a result the monostable is triggered and a short pulse is applied to the clock input (pin 14) of IC 7493, which is a counter IC. Thus Q1 output (pin1 &12) of IC 7493 becomes high and transistor T2 is forward biased to ON state and the relay is energized. These results in shorting of power supply contact to the bulbs or any equipments and thus switching ON the bulbs or any equipments.

 

 Touch sensitive burglar alarm for internal security

               This simple circuit when connected to a metal locker or cupboard generates an alarm when touched by an undesired entity.

            The transistor gets saturated by just touching its base. Here is a simple, low cast touch switch with alarm based on this idea. The 50 Hz hum present in our body is the key to this circuit. BC 549 transistor has been chosen for this circuit. The circuit is basically a burglar alarm with timer. Timer circuit is a monostable multivibrator. Initially voltage at pin 2 of IC 1 is low.

            If the sensor, which is the base of the transistor T1 is touched by the finger (even the slightest, touch will do) transistor T1 is saturated. Now the voltage at pin 2 of IC 1 is greater than 1/3 Vcc. As a result IC 1 gets a trigger pulse at its trigger input pin 2. Therefore its out goes high for a predetermined time period. The period can be adjusted by varying the value of resistor R1 or capacitor C1 as T=1.1*R1*C1 sec.

            The siren circuit is build around IC 2 (UM 3561). Since the output of IC 1 is high, the IC 2 gets power supply. The output from IC 2 is amplified by transistor to drive an 8-ohm, 500mw load-speaker.

 

 

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