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18 Jun 2014

This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered. The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1.

The NPN transistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its reset pin becomes high. When the Laser / IR beam breaks, current through the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.

A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.

555 Photodiode alarm - [Link]

2 Jun 2014

IMG_3538_1600x1200_851-600x372

Markus Gritsch build another bedside table alarm clock, the schematic and source code is available here:

recently some vintage bubble displays popped up at various places [1][2], so I felt the urge to build another bedside table alarm clock, this time a really tiny one, roughly the size of an AAA battery.

Bubble display alarm clock - [Link]

21 Apr 2014

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hertzgamma @ instructables.com writes:

This instructables will show you how to make an alarm system that will beep a buzzer if you leave the fridge door opened for a long time to remind to you to close the door. All new fridges on the market have this option built in, but some may want to upgrade their old fridges.

Fridge Door Detector Alarm - [Link]

27 Mar 2014

We are always vulnerable to thieves but we don’t know when will they strike. When they do, it will be too late for us to notice that our property was already taken. This project helps alert the owner if a thief is picking a lock. It can be used on doors, luggage or anything else with a lock.

The concept is simple, if the lock is opened without our consent, an alarm will be turned on indicating an intruder. This circuit is based on a NAND gates configuration that will turn the switching side on or off.

In this project we used the HEF4011B, a quad 2-input NAND gate. The outputs are fully buffered for the highest noise immunity and pattern insensitivity to output impedance. The configuration of the IC HEF4011B produces a HIGH output if the input is HIGH. Based on the figure, when the wire loop is closed, the IC HEF4011B will have a LOW input, and when the wire loop is triggered, the IC HEF4011B will have a HIGH input which will make its output also HIGH. The HIGH output of the IC HEF4011B will then be inputted to the base of the BC547 transistor allowing the current to flow on the relay switching the indicator or the buzzer ON.

Components:

  • HEF4011B quad 2-input NAND gate
  • BC547 transistor
  • 1N4007 diode
  • 1kΩ resistor
  • 4.7kΩ resistor
  • 0.1µF capacitor
  • Relay
  • 5V dc power source

Anti-theft Security Alarm Circuit – [Link]


8 Dec 2013

Application:

An IR detector that sounds a buzzer when an IR beam is broken, meaning the IR signal is lost.  A pulsed IR signal generator is necessary, but not included in this post.  This project would be ideal for doorwaLM311ys or hallways to alert when someone enters or exits an area.

Description:

The IR sensor responds to pulsed IR, not ambient or continuous IR.  This means that another transmitter project is necessary in order to complete this one!  Note though that some forms of lighting like fluorescent lighting may interfere with the sensor.  For convenience,  the the buzzer is internally driven so that a only Vdc is needed to make a sound.  In this case, the IR sensor senses 38kHz pulsed infrared light.

Pin 3 of the IR sensor is actually low (0V) while receiving a signal.  When the sensor is blocked from receiving the IR signal, the sensor outputs a high signal to the comparator, which then allows current through the LED/Buzzer circuit, and alerting you that the beam is broken. In the Scheme-It drawing the LM311 IC is a grouping of three components, in a functional block diagram style, to show how it functions in the circuit beyond what the pinouts would show normally.

IR Beam Breaker Alarm Circuit - [Link]

17 Jul 2013

BZB_1

T.K. Hareendran writes:

All items stored in a deep freezer will thaw out if, for some reason, the temperature inside the freezer rises to the thaw point. However, a freezer monitor alarm can warn you of the rising temperature before the thaw point is reached.

This simple circuit is powered by regulated 9V and built around a few discrete components that are readily available in the market. Current consumption of the circuit is only a few milliamperes in idle state. So you can also use a 9V 6F22/PP3 type compact battery for powering the circuit.

Freezer Monitor Alarm - [Link]

12 Jul 2013

Markus Gritsch shows off his Dot-Matrix MSP430 alarm clock. [via]

Dot-Matrix MSP430 alarm clock - [Link]

11 Jul 2013

At the heart of this circuit is a precision integrated temperature sensor, LM35 (IC1), which provides an accurate linear and directly proportional output in mV, from 0 to +155 degrees C.  Designed to draw a minimal current of its own, the LM35 has very low self heating in still air. Here the output of the LM35 is applied to the non-inverting input of a comparator wired around a CA3130 opamp (IC2). A voltage divider network R3-P1 sets the threshold voltage, at the inverting input of the opamp. The threshold voltage determines the adjustable temperature trip level at which the circuit is activated.

When the measured temperature exceeds the user-defined level, the comparator pulls its output High to approx. 2.2 V causing transistor T1 to be forward biased instantly. T2 is also switched on, supplying the oscillator circuit around IC3 with sufficient voltage to start working. The 555 set up in astable mode directly drives active piezoelectric buzzer Bz1 to raise a loud alert. Components R7, R8 and C4 determine the on/off rhythm of the buzzer.

Overheat Detector Alarm - [Link]

20 Jun 2013

0909_01

Boris Landoni writes:

It’s small but packed with features. The GSM alarm we present today, sports a PIR motion sensor, can be battery operated and it’s capable to communicate via GSM. It can transmit alarm conditions and receive commands from remote. It’s also capable to indicate problems such as is insufficient voltage supply or tampering.

It’s not so conventional for antitheft system: to integrate a movement sensor, a PIR motion sensor and a temperature probe in a single appliance: all this accompanied by an SMS sending GSM / GPRS module. This circuit was born as a very versatile, ready to use, built-in alarm system: no installation is required, you can just drop it and it’s ready to work. It’s not by chance that is designed to be battery operated: it also features a battery state control to check the power.

GSM Multifuction Alarm with SIM900 - [Link]

9 May 2012

mattwilliamson/arduino-sms-alarm.

An Arduino based burglar alarm that sends an SMS when motion is detected. It will send an SMS to you every 30 minutes while motion is detected (configurable).

Arduino burglar alarm sends SMS - [Link]



 
 
 

 

 

 

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