Call Bell With Welcome Indication

Here is a simple call bell circuit  that displays a welcome message when somebody presses  the call bell switch momentarily. the  alphanumeric display can be fitted  near the call bell switch. the circuit is built around two  555 ICs (IC1 and IC2), seven KLA511  common-anode alphanumeric displays  (DIS1 through DIS7) and a few discrete  components. For easy understanding,  the eentire circuit can be divided into  two sections: controller and display.  the controller section is built around  IC1 and IC2, while the display section  is built around alphanumeric displays  (DIS1 through DIS7). As shown in the circuit, both IC1  and IC2 are wired as monostable  multivibrators having time periods  of around 5 seconds and 2 minutes,  respectively. You can change the  time period of IC1 by changing the  values of resistor R12 and capacitor  C3. Similarly, the time period of IC2  can be changed by changing the values of resistor R2 and capacitor C1.  Alphanumeric displays DIS1 through  DIS7 are wired such that they show  ‘WELCOME’ when the output of IC2  goes high.
The circuit is powered by a 6V battery. Else, you can use the 6V, 300mA power adaptor that is readily available  in the market. the 6V battery or power  adaptor provides regulated 6V required to operate the circuit. A 6V DC  socket is used in the circuit to connect the output of the adaptor if you don’t use the battery.
Working of the circuit is simple.  First, power-on the circuit using switch  S2. LED1 glows to indicate presence of power supply in the circuit. Now if you press call bell switch S1  momentarily, it triggers
both the timers (IC1 and  IC2) simultaneously. IC1  produces a high output  at its pin 3 for about
five seconds. transistor  t2 conducts and piezobuzzer PZ1 sounds for about five seconds  indicating that there is  somebody at the door.  At the same time, IC2  too produces a high out- put at its pin 3 for about  two minutes. transistor  t1 conducts to enable  the alphanumeric displays. the word ‘WEL-COME’ is displayed for about two minutes  as DIS1 through DIS7  ground via transistor T1.  If switch S1 is  pressed again within  these two minutes, piezobuzzer PZ1 again  sounds for five seconds  and the display continues to show ‘WELCOME’.
Assemble the complete circuit on a general-purpose PCB and  house in a small cabinet  with call bell switch S1  and LED1 mounted on  the front panel. At the  rear side of the cabinet,  connect a DC socket for  the adaptor. Install the  complete unit (along  with the display) at the  entrance of your house.  Connect the 6V battery or 6V adaptor for powering the circuit. Configure switch  2 (used to enable/disable the call bell)  in a switch board at a suitable location  inside your house. If you don’t use a battery, connect the power adaptor
to the DC socket on the rear of the  cabinet. Close switch S2 only when  you want to activate the circuit with battery. Otherwise, keep it open when  the 6V adaptor is in use.
ßE note. 1. To avoid any shorting during rain, waterproof the entire circuit assembly including alphanumeric displays (installed at the entrance) by  covering it properly.
2.  the complete kit for this circuit is available with ßE associates kits’n’spares.

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