Electronics Door-Knock or Vibration Alarm

This is a simple circuit that activates an alarm when there is a knock on the door or there are any vibrations due to movement of heavy goods or furniture. The circuit uses readily available components.
 
Circuit and working :-

The circuit is built around quad-opamp LM324 (IC1), which is configured in amplifier mode. It uses the piezoelectric element of a piezo buzzer as the input sensor, two transistors BC547 (T1 through T2), a piezo buzzer and some other components for the alarm circuit. Fig. 1 shows the circuit diagram of the door-knock alarm.The reference voltage at pin 3 of IC1 is set by trimming potmeter VR1. The piezoelectric element plate is fixed at the centre of the door using cello tape. Apply a small quantity of adhesive on the edges between the plates. Wires from the piezo element are connected at CON2. These generate an input pulse when vibrations are caused by knocking on the door. The pulse is amplified by op-amp A1 of IC1. Remaining three op-amps of quad IC LM324 are not used here.
The output of A1 of LM324 from pin 1 is further amplified by transistors T1 and T2 to drive the piezo buzzer or relay. Because of the presence of high-value capacitor C5, the buzzer remains active for a few seconds. The circuit is powered by 9V/12V power supply. Sensitivity of the circuit can be adjusted by 1M potmeter VR1.
In place of piezo buzzer PZ1, you can use 9V/12V single-changeover relay connected to an amplifier for louder sounds.


Comments

Post a Comment

Popular posts from this blog

Turning on an LED with your Raspberry Pi's GPIO Pins

Image
One of the biggest selling points of the Raspberry Pi is its GPIO, or General Purpose Input/Output ports.  They are the little pins sticking out of the circuit board and allow you to plug various devices into your Pi.  With a little programming, you can then control them or detect what they are doing. In this tutorial I am going to show you how to light an LED.  In addition to your Raspberry Pi running Raspbian, what you will need is: A Breadboard An LED A 330 ohm resistor Two Male-Female jumper wires You can get all these, and more, in the £5 CamJam EduKit from The Pi Hut, which teaches you more about LEDs, buzzers and switches, and includes all the hardware and eight well-written worksheets about using the GPIO pins on your Pi. The Breadboard The breadboard is a way of connecting electronic components to each other without having to solder them together. They are often used to test a circuit design before creating a Printed Circu...
Read more

Simple SMPS

Image
circuit and working Fig shows the circuit of a simple 12V, 1A SMPS. The circuit is built around a low-power offline switcher TNY266 (IC1), photo-transistor photo-coupler EL817 (IC2), a flyback transformer (X1) and some other easily-available components. Low-power offline switcher (TNY266). The SMPS here has been designed using a TNY266 chip, which is affectionately called the ‘555’ of SMPS. This device has a 700V power MOSFET, an oscillator, a high-voltage switched current source, a current limiting and thermal shutdown circuitry integrated onto a monolithic device. The start-up and operating power is derived directly from the voltage on the drain (pin 5), eliminating the need for a bias winding and associated circuitry. In addition, the device incorporates auto-restart, line under-voltage sense, and frequency jittering. The drain-source breakdown voltage of the MOSFET in TNY266 is important. During the ‘off’ period, the MOSFET sees rectified 317V DC approximately. Addit...
Read more

Efficient LED Blinking for Embedded Systems

Image
 Efficient LED Blinking for Embedded Systems:- Smart hardware design can simplify the embedded software and make it more reliable. Designers use blinking LED signals to indicate different status and for inbuilt testability. Making an LED array blink requires an individual software loop for each LED or an individual timer and specific software to serve it. This can be an issue in a system that uses low-level MCUs which provide limited resources. The circuit presented here solves this problem by adding a simple hardware comprising low-cost inverters with Schmitt trigger for blinking as many LEDs as required. Circuit and working Fig shows the circuit for efficient LED blinking for embedded systems. It uses different arrangements to make five different LEDs (LED1 through LED5) blink at individual rates. The circuit is built around 74HC14 (IC1) containing six inverters with Schmitt triggers at the inputs. The frequency of blinking is usually selected in the 0.2-20...
Read more