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The circuit has been designed to provide an alarm with the use of a buzzer when sensing high temperature by using a thermistor. Thermistor – one type of resistor used as temperature-sensing element which demonstrates a large change in resistance proportional to a small change in temperature because of the composition of its semiconductor material. BC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment. The temperature can be regulated by the design of this circuit and it can provide a warning scheme in the case of excessive increase in the temperature. The control of the temperature starts from the thermistor TH1 which contains a negative factor. Since this component has resistance proportional to the temperature that it detects, the resistance can be modified wherein a 10K ohm resistance is produced ate 25° C while 1K ohm resistance will be produced at 94° C. to define a specific value of temperature, a trimmer...

The alarm may be used for a variety of applications, such as frost monitor, room temperature monitor, and so on. In the quiescent state, the circuit draws a current of only a few microamperes, so that, in theory at least, a 9 V dry battery (PP3, 6AM6, MN1604, 6LR61) should last for up to ten years. Such a tiny current is not possible when ICs are used, and the circuit is therefore a discrete design. Every four seconds a measuring bridge, which actuates a Schmitt trigger, is switched on for 150 ms by a clock generator. In that period of 150 ms, the resistance of an NTC thermistor, R11, is compared with that of a fixed resistor. If the former is less than the latter, the alarm is set off. When the circuit is switched on, capacitor C1 is not charged and transistors T1–T3 are off. After switch-on, C1 is charged gradually via R1, R7, and R8, until the base voltage of T1 exceeds the threshold bias. Transistor T1 then comes on and causes T2 and T3 to conduct also. Thereupon, C1 is charged v...

Touch Alarm circuit is widely used for security, which is installed on the door. The advantages of this alarm is because the cost is cheap and difficult to detect by burglars / intruders. The following is an example of a touch of alarm circuit which is designed by Tony Van Roon.   Components List : R1 = 100K R2 = 56K R3 = 10M R4 = 220K P1 = 100K D1 = 1N4004 T1 = 2N3904, or equivalent U1 = 555 Timer* C1 = 47μF/16V** C2 = 33μF/16V** Re1 = Relay*** Notes: *The 555 can be a LM, NE, or MC(cmos) type, they’re all pin-compatible. **C1/C2′s operating voltage should be elevated to 25V if you decide to go with a 12V energy source. Rule of thumb: the operating voltage of capacitors are at least double the supplied voltage, in other words, if the powersource is 9Volt, your capacitor(s) is a minimum of 18V. Transistor T1 could be any approximate substitute. *** Use any suitable relay for the project and if you are not tight on area, use any size. I’ve develop this specific circui...

This circuit disables an alarm clock on Saturdays and Sundays when people like to sleep in but enables normal operation on Mondays to Fridays so that people rise in time for work or school. The core of the circuit is a 4017 decade counter which acts as the day counter and it is used in conjunction with a desk clock which acts the alarm and a watch module with alarm function which provides one clock pulse very day to the 4017. In operation, the watch module feeds a day pulse via transistor Q3 to the clock input of IC1. This has seven outputs connected via day switches (S1-S7) and diodes D3-D9 to Q1 which disables the alarm signal to the speaker via transistor Q2. LEDs1-7 indicate the actual day (if you forget!). Circuit diagram: Alarm Clock With Day Selector Circuit Diagram To set the system, set the desk clock for the correct time and for the desired alarm time (eg, 6’o’clock). The watch module is set to the correct time and its alarm set to midnight. The day counter, IC1, is set to ...

This is the Cheap and Simple Gate Alarm Circuit Diagram. A cheap and simple gate alarm made from a single CMOS Integrated Circuit.    Cheap and Simple Gate Alarm Circuit Diagram Circuit Notes Figure 1 represents a cheap and simple Gate Alarm, that is intended to run off a small universal AC-DC power supply. IC1a is a fast oscillator, and IC1b a slow oscillator, which are combined through IC1c to emit a high pip-pip-pip warning sound when a gate (or window, etc.) is opened. The circuit is intended not so much to sound like a siren or warning device, but rather to give the impression: "You have been noticed." R1 and D1 may be omitted, and the value of R2 perhaps reduced, to make the Gate Alarm sound more like a warning device. VR1 adjusts the frequency of the sound emitted. IC1d is a timer which causes the Gate Alarm to emit some 20 to 30 further pips after the gate has been closed again, before it falls silent, as if to say: "I'm more clever than a simple on-off devic...

This circuit uses a NE555 timer and CD4020B. When +12 Vdc is applied to the circuit, the output of IC2 is set low via C2, which turns on the relay, and IC1, a pulse generator. Auto Turn-Off Alarm With 8-Minute Delay Circuit Schematic IC1 pulses counter IC2. After 8192 clocks, IC2 output (pin 3) goes high, cuts off Q2, and completes the cycle.

This is a Simple Auto Turn-Off Alarm With 8-Minute Delay Circuit Project. This circuit uses a NE555 timer and CD4020B. When +12 Vdc is applied to the circuit, the output of IC2 is set low via C2, which turns on the relay, and IC1, a pulse generator. IC1 pulses counter IC2. After 8192 clocks, IC2 output (pin 3) goes high, cuts off Q2, and completes the cycle. Simple Auto Turn-Off Alarm With 8-Minute Delay Circuit Diagram

ADVANCED TOUCH SENSITIVE BURGLAR ALARM CIRCUIT Now i am going to introduce you Touch sensitive security alarm. I hope as the name itself gives you a clear view about the circuit and its function. The circuit alarms whenever an unauthorised person trying to access your costlier materials. This circuit is portable, cheap, and effective. Keep the touch plate on your metal knob, door knob, gate...... Where you want to restrict the misuse. Note:- The Touch plate should be conducting. Other useful links:- Touch sensitive switch Working of NE555 as astable multivibrator

This is a simple circuit of low-cost door knock alarm with timer. This is low-cost circuit uses the piezoelectric element of a piezobuzzer as the input sensor. The piezoelectric element plate is fixed at the centre of the door wing by using a cello tape. Apply a small quantity of adhesive at the edges between the plate and the door. Extend wires about 1-1.5 metres from the piezoelectric to the circuit. IC NE555 (IC1) is configured in monostable mode. Low-Cost Door KnocK Alarm With Timer Circuit Diagram: When it gets an input pulse its output goes high for a period set by VR1, resistor R5 and capacitor C3. IC UM66 (IC2) is used as a melody generator. When the door is knocked at, the piezo plate generates an input pulse, which is amplified by transistor T1. The amplified signal triggers the timer IC NE555 and its output pin 3 goes high to enable the melody generator. Music is heard from the speaker LS1. After the set time period, the melody sound stops. Assemble the circuit on a general-...

SIMPLE LASER BURGLAR ALARM CIRCUIT It is an advanced, simple, efficient and low cost circuit. You can use this circuit on Home, office, locker or anywhere for Security purpose. As the name suggests, the circuit is based on Laser. We all know about the features of Laser, Long Range, pointed beam, Low power consumption and so on. The Transmitter section of this circuit is a LASER. Circuit Diagram of Laser Burglar Alarm Components Used In Laser Burglar alarm circuit IC TLO71 T1 L14F1 (Photo Transistor) T2 BC 548 R1 1KΩ R2 4.7KΩ R3 4.7KΩ R4 100Ω C1 470μF C2 1000μF LED Buzzer 9V Battery Working of Laser Intruder/Burglar Alarm Circuit. This circuit alarms whenever someone cross the Laser beam transmitted from a LASER. The output of IC TL071 goes high whenever their is no Light(Laser) Ray. This output voltage is further amplified by means of a NPN transistor Q2, which will drive the buzzer and generates an alarm. How to Setup Laser Burglar Alarm? As i mentioned above, you can use an ordinary...

Burglar alarm circuit or Theft alarm circuits are available in several forms. The above circuit was one of that kind using timer IC 555 as the main component. The circuit is very easy to construct and the cost of this circuit is also very less. So we can implement this circuit by our own and install this circuit in our home so that you can improve your knowledge and it also adds protection to your home. Using IC 555 Burglar Alarm Circuit Diagram The working of this circuit is very easy to understand.In the above circuit IC 555 was used as a Astable multivibrator.The Astable multivibrator puts out a continuous stream of rectangular pulses having a specified frequency. Thus by using the Astable multivibrator we can produce continuous frequency which was given as input to the speaker which makes an alarm sound in case of any disturbance in its trip wire. Pin diagram of IC 555 was given below for your better understanding. Now we can see how we can change the Astable Multivibrator to a ala...

Here is a Low-cost Electronic Circuit Project of Flashing Signal Alarm with LEDs Circuit. Flash signals for the AO-543 modules are derived form the fast- and slow flash outputs. The fast flash signal is generated by a oscillator circuit.A LED  flashing briefly once every 5 seconds to imitate the indicator of a real alarm is the function of this dummy alarm project with the use of a 7555 timer IC.This circuit is useful if you need a low-energy flashing alarm. Low-cost Flashing Signal Alarm with LEDs Circuit Diagram: The 200 to 400-dc supply should have enough internal resistance to charge the 0.5 capacitor between flashes, about 2 or 3 time constants, which means about 500 kQ to 1 for a 1-s rate.Use lower values for higher rates.The Signalalarmfunction shall cause the system to generate a SIGALRM signal for the process after the number of realtime seconds specified bysecondshave elapsed. Processor scheduling delays may prevent the process from handling the signal as soon as it is ge...

A timed Bell/Siren Cut-Off. It’s designed to be used with the usual types of normally-closed input devices such as – magnetic reed contacts – micro switches – foil tape – and PIRs.

Simple Anti Bag Snatching Alarm Circuit Diagram . The heart of this entire circuit anti bag snatching alarm is operational amplifier IC CA3140 (IC 1 ), configured as a comparator. The two inputs (inverting and non – inverting) is given to pin no 3 and 2 of operational amplifier respectively and output is obtained from pin no 6. Here IC 2 (timer IC NE555) is used as monostable multivibrator. The timing component of anti bag snatching alarm is R 5 , VR 1 , and capacitor C 2 with the given value in this circuit diagram lets the time of timer is about 1 minute. For audio section, IC 3 is used as alarm tone generator with an inbuilt oscillator. Finally the output is obtained from pin no 3 of IC 3 and amplified by transistor T 1 in order to get desire level and lastly fed to loudspeaker for output. Simple Anti Bag Snatching Alarm Circuit Diagram PARTS LIST Resistors (all ¼-watt, ± 5% Carbon) R 1 , R 2 , R 3 = 100 KΩ R 4 , R 6 = 10 KΩ R 5 = 10 MΩ R 7 = 330 Ω R 8 = 220 KΩ R ...

This electronic circuit is a very nice and simple alarm circuit that is based on the 555 timer integrated circuit. This alarm circuit can be used with many types of sensors like : light or temperature sensors. As you can see below some types of sensors that can be connected at this type of alarm circuit ( darkness , light , cold and heat sensor ). If the sensor detects that the temperature or light is outside of the desired range the alarm will be activated .By turning the  potentiometer from the base of Q1  you will modify the sensibility of the sensor . When the alarm is activated the Q2 transistor acts as an audio amplifier and speaker driver for the 16 ohms speaker . This alarm circuit require a 12 volts DC power supply circuit .

This electronic circuit is a very nice and simple alarm circuit that is based on the 555 timer integrated circuit. This alarm circuit can be used with many types of sensors like : light or temperature sensors. As you can see below some types of sensors that can be connected at this type of alarm circuit ( darkness , light , cold and heat sensor ). If the sensor detects that the temperature or light is outside of the desired range the alarm will be activated .By turning the  potentiometer from the base of Q1  you will modify the sensibility of the sensor . When the alarm is activated the Q2 transistor acts as an audio amplifier and speaker driver for the 16 ohms speaker . Dual Sensor 555 Timer Alarm Circuit Diagram This alarm circuit require a 12 volts DC power supply circuit .