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    This simple Door Chime protects the door and gives a loud Alarm tone when there is an attempt of theft. The circuit is too simple and battery operated.

    A Normally Closed (NC) reed switch and magnet is used to trigger the circuit. Alarm generator is the popular ROM IC UM 3561. This 8 pin IC has an inbuilt oscillator to generate 4 siren tones like, Ambulance siren, Police siren, Fire brigade siren and Gun sound. The different tones can be selected using its pin 6 connected to VCC, Ground or not connected. Frequency of oscillation is determined by the 220K resistor connected to the pins 7 and 8 of the IC.UM 3561 is the low power IC and its maximum voltage rating is 3 volts. So Zener diode ZD is used to give 3 volts supply to IC. Medium power NPN transistor T1 amplifies the output pulses from IC1 to a loud siren.

    Tiny Door Guard Circuit

    Magnet can be a small sized one that is to be fixed in the door using double sided adhesive tape. Fix the circuit board in the door frame. Fix Reed switch in the door frame, very close to the door. So that, when the door is closed, the magnet will pull the contacts of the reed switch to break supply to the IC. When the door opens, contacts of the reed switch make contact and IC gets power to give alarm.

    attentionThe author D Mohankumar is not an active member anymore. Please take into consideration that the presented information might not be correct.
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    17 Responses to "Tiny Door Guard with Alarm"

    1. excellent

    2. Respected sir,
      In your ckt BD139 is shown like a darlington transistor pair.Is it right?I am an ITI student;please.

      • D.Mohankumar says: on October 9, 2010 at 6:11 pm

        Dear Arjun

        BD 139 is a Medium power NPN transistor. Mistake in the description is corrected. Thanks for pointing out the error

    3. Thanks for a nice easy door alarm. I was wondering how to replace the magnetic switch with a refective opto isolator devise to make this into a “interupte the light beam to alarm” divice. The 9v battery would last forever. I need some thing to keep track of my mom when she comes out of her bedroom. I am taking care of her as she has Alzheimers disease.
      They make several IR devices on the market real cheap but having spent 20 years of my life as a electronic equipment repair tech and done some of my own designs I thought it would be funner to build my own or maybe use a modified version of yours?

      Thanks , Darcy Roberts, Central Oregon, USA

    4. I was wondering if it is possible to add a LED to to the circuit……..thanks 😀

      • D.Mohankumar says: on November 20, 2010 at 3:36 am

        you can add an LED with a resistor in series with the lower side of the reed switch. When the door opens, reed switch make contact and LED lights along with alarm.

    5. sir, i would like to ask if there is a possible replacement for um3561.

    6. brilliant…..

    7. TO : Mr.Mohankumar

    8. I was constructed your circuit but it sounds very low.please help to increase the intensity of siren sound.please inform as fast as possible.thank you

    9. I got a circit about door alarm

    10. I am looking mobile repeller can I get a ckt

    11. Hey sir…please do me a favor on my question. There is one sentence that make me confuse = “When the door opens, contacts of the reed switch make contact and IC gets power to give alarm.” Is it mean that anytime the door open then the alarm will ring ? This does not make sense if the owner open the door and the alarm also ring right ? Please help me to release my confuse :)

    12. is there any other way to replace the switch?

    13. Thanks for another knowledge inpartation, sir i love to build ur cicuit after you. Pleased sir i can’t understand how place this device the way you said. Pleased sir, kindly help me illustrate your explanations. Thanks.

    14. how to make a circuit on breadboard ???

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