Saturday, June 29, 2013

Automatic Programmable School Bell Timer Circuit

The post explains a very simple 10 stage long duration programmable timer circuit which can be used as a school bell timer circuit. All the 10 stages can be individually programmed from zero to 5 hours. The circuit can be modified in many different ways to suit other specific related applications.


Normally in most of the schools even today the period bells are rung manually by the concerned staff or the peon. Although the job is quite traditional and is carried out without much difficulty and reasonably accurately, the concerned person has to be always on a stand by position for implementing the actions.

However with the help of a simple electronic circuit the above implementations could be made fully automatic, eliminating human intervention, thus saving a lot of inconvenience and time.

The functioning of the proposed automatic school bell period timer circuit may be understood with the following points:

At the first glance the circuit might look quite complex, but seeing it closely shows that actually it's very simple, just a repetition of identical stages for the required number of times.

We'll try to understand the top left stage and that will clarify the entire circuit within no time.

The circuit is based on the timer/oscillator chip 4060. It's wired in its usual timer/counter mode with the help of the resistors and capacitors fixed over its pin#9, 10,11. Rx determines the time period for which the IC counts until its pin#3 becomes high.

The value of this resistor may be determined through trial and error for acquiring the required time intervals for all the relevant subsequent stages.

The design is repeated for all the stages.

However the top left stage being the first power switch ON stage is rigged with additional components.

When the push button P is pressed, the SCR latches, grounding pin#12 of the IC.

This initiates the counting procedure within the IC. After the predetermined time lapses, pin#3 of the IC goes high and also the stage gets latched via the diode connected to pin#11.

With pin#3 high, the associated transistor pulls pin12 of the next stage to ground, which in turn initiates the  counting of the second stage.

The procedure is repeated exactly the same way for the second stage also, and consequently all the corresponding stages get activated serially one after the other as per the set time for the individual stages.

When the the time period for the last stage is elapsed (bottom left), the transistor at pin#3 momentarily grounds the anode of the SCR via the 1uF capacitor switching off the SCR and the entire circuit. The situation resets the whole circuit to its original state, until the push button is pressed the next morning for initiating yet another cycle.

The second circuit shows the driver stage which is responsible for ringing the AC bell in response to the triggering of each subsequent stages in the given order.

The diode ends are connected to pin#12 of the different stages. The moment these pins are pulled to ground by the BC547 transistors, sends a momentary biasing to the BC557 transistor which in turn activates the connected relay and the load for a brief period of time depending upon the values of the transistor base resistor and the capacitor (chosen arbitrarily here)







11 comments:

  1. Hi SM , I want a circuit which sounds the door bell when somebody opens the front metal gate of the house . Also I require a door bell which works at 12 V . As I supply these circuits with solar powered 12 V batteries .

    ReplyDelete
    Replies
    1. You can do it by simply adding a door switch with the front gate and wiring the switch with the bell and the 12V supply.

      switches which are used in car doors can be used for this application.

      Delete
    2. I want to do it using Transistors and ICs . Please provide a circuit

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    3. Hi SM , I found this circuit which is exactly what I need ,

      http://8085projects.info/automatic-door-bell-with-infrared-transceiver.html

      there has been no information about IC2 and IC3 in that circuit . Can you tell which generally available ICs can be used for these two and what should be used for receiver part i.e Photo diode or photo transistor ??

      Finally can I power the circuit using 12 V Battery ?? Help me , Thank you

      Delete
    4. IC2 = MPC1373 its given in the article.

      no idea about IC3, may be a UM66 can be used but differently not as shown in the diagram.

      Delete
    5. NTE1714S is an equivalent for IC MPC1373

      http://www.weisd.com/store2/NTE1714S.pdf

      Both of these ICs are not available at local store . Can you please suggest a generally available IC for this IC . It looks like an op-amp in the diagram . Can I use 741 IC for that ?? Please post a similar circuit using generally available ICs and UM66 for my needs ..

      I really need your help SM as some kids sneak into my house's front gate and destroy plants in the small garden in front of my house and also it notifies if any guest visits the house . It is neccesary for me . Hope you will help .


      Thank you

      Delete
  2. hello sir Swagatam Majumdar. I have a question ... you have a hall light timer circuit when a person passes automatic ON y automatic OFF with variable timer. thank you very much.

    miguel

    ReplyDelete
    Replies
    1. hello miguel,

      you may refer to the circuits explained in the following article, it may be modified as per your requirement:

      http://homemadecircuitsandschematics.blogspot.in/2012/09/pir-controlled-led-driver-circuit.html

      Delete
  3. can please upload a mini project based on process control timer

    ReplyDelete

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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.