Alarm triggers on after a 13 second delay and stays on for 1-1 Vfe minutes. Then it resets automatically It can also be turned off and reset by opening and reclosing SI.
Automotive Burglar Alarm Circuit Diagram:
Power Resumption Alarm and Low-Voltage Protector
The circuit described here protects your electrical appliances like AC motors from damage due to low voltage at power-on. It remains standby without giving power to the load after power resumes. The load can be switched on only manually. This prevents damage to the device if it is 'on' when power resumes.
unregulated power supply is derived from a 12V-0-12V, 300mA step-down transformer and rectifying diodes D2 and D3. The rectified DC is made ripple-free using capacitor C3. An audio/video indicator (piezobuzzer and LED3) is provided along with the power supply for power resumption.
When power is switched on, capacitor C4 charges through the piezobuzzer and LED3, making both of them active. The piezobuzzer beeps and LED3 glows for a few seconds. When capacitor C4 is fully charged, the cathode of the LED becomes high inhibiting further flow of current through the buzzer.
When the power is off, capacitor C4 discharges through resistor R9.
The circuit uses IC CA3140 (IC1) as a voltage comparator to detect voltage changes in the unregulated power supply due to AC mains. Mains voltage changes in the primary as also the secondary winding of the transformer, which is sensed by IC1 to energise/de-energise the relay. Zener diode ZD1 provides a reference voltage of 3V to make transistor T1 conduct. Preset VR1 adjusts the breakdown point of ZD1.
Fig. 1: Power supply circuit with resume indicator
When the voltage level is normal, zener diode ZD1 breaks down and transistor T1 is forward-biased. Capacitor C1 provides time delay of a few seconds to avoid any fluctuation affecting the device during power-on. When transistor T1 conducts, the inverting input (pin 2) of IC1 goes low. However, IC1 does not give a high output as its power supply depends on the conduction of SCR1 (BT169). So manual operation is necessary to energise the relay.
When push-to-on swish S1 is pressed, SCR1 fires to provide voltage to IC1 at its pin 7. As the voltage level at the non-inverting input (pin 3) of IC1 is half of the supply voltage, its output becomes high and the relay (RL1) energises. LED2 glows to indicate the high output of IC1 and activation of relay.
When the line voltage goes below 180V, the secondary voltage of the transformer also drops, say, below 12 volts, ZD1 cease to conduct and the collector of T1 becomes high. This high voltage at the inverting input (pin 2) of IC1 makes its output low. The relay de-energises to stop power to the device.
Fig. 2: Low-voltage Protector Circuit Diagram
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Use a 12V PCB-mounted relay. Provide holes for LEDs and switch S1 on the front side of the case. Connect AC power voltage to the motor (load) through the common and normally-open (N/O) contacts of the relay. After assembly and checking the circuit, switch on the circuit and wait for a few minutes. LED1 will gradually become bright due to the charging of capacitor C1. Press S1 to energise the relay. Adjust VR1 so as to make LED1 fully on. This will allow easy latching of the relay
Source Link: www.w3circuits.com
unregulated power supply is derived from a 12V-0-12V, 300mA step-down transformer and rectifying diodes D2 and D3. The rectified DC is made ripple-free using capacitor C3. An audio/video indicator (piezobuzzer and LED3) is provided along with the power supply for power resumption.
When power is switched on, capacitor C4 charges through the piezobuzzer and LED3, making both of them active. The piezobuzzer beeps and LED3 glows for a few seconds. When capacitor C4 is fully charged, the cathode of the LED becomes high inhibiting further flow of current through the buzzer.
When the power is off, capacitor C4 discharges through resistor R9.
The circuit uses IC CA3140 (IC1) as a voltage comparator to detect voltage changes in the unregulated power supply due to AC mains. Mains voltage changes in the primary as also the secondary winding of the transformer, which is sensed by IC1 to energise/de-energise the relay. Zener diode ZD1 provides a reference voltage of 3V to make transistor T1 conduct. Preset VR1 adjusts the breakdown point of ZD1.
Fig. 1: Power supply circuit with resume indicator
When the voltage level is normal, zener diode ZD1 breaks down and transistor T1 is forward-biased. Capacitor C1 provides time delay of a few seconds to avoid any fluctuation affecting the device during power-on. When transistor T1 conducts, the inverting input (pin 2) of IC1 goes low. However, IC1 does not give a high output as its power supply depends on the conduction of SCR1 (BT169). So manual operation is necessary to energise the relay.
When push-to-on swish S1 is pressed, SCR1 fires to provide voltage to IC1 at its pin 7. As the voltage level at the non-inverting input (pin 3) of IC1 is half of the supply voltage, its output becomes high and the relay (RL1) energises. LED2 glows to indicate the high output of IC1 and activation of relay.
When the line voltage goes below 180V, the secondary voltage of the transformer also drops, say, below 12 volts, ZD1 cease to conduct and the collector of T1 becomes high. This high voltage at the inverting input (pin 2) of IC1 makes its output low. The relay de-energises to stop power to the device.
Fig. 2: Low-voltage Protector Circuit Diagram
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Use a 12V PCB-mounted relay. Provide holes for LEDs and switch S1 on the front side of the case. Connect AC power voltage to the motor (load) through the common and normally-open (N/O) contacts of the relay. After assembly and checking the circuit, switch on the circuit and wait for a few minutes. LED1 will gradually become bright due to the charging of capacitor C1. Press S1 to energise the relay. Adjust VR1 so as to make LED1 fully on. This will allow easy latching of the relay
Source Link: www.w3circuits.com
Auto Alarm Schematic
SI is external key switch. The alarm allows a 0- to 45-s delay after SI is operated before the circuit is armed. During this period, LED1 lights green. After this delay, LED1 lights red, which indicates that the circuit is armed.
Auto Alarm Circuit Schematic
Then, sensors S2 through S4 -(NO) or S5 through S6 (NO) pull pin 2 of U2 low, which activates K1 and sounds the alarm. The alarm sounds for a duration determined by R4 and C2. After this time, K1 releases and the circuit is again ready. Manual reset is via the key switch, SI.
Source Link: www.w3circuits.com
Digital Alarm Clock Using PIC
This project describes a digital clock with alarm function. It uses a PIC16F877 microcontroller to generate an accurate 1 sec delay with Timer0 using Roman’s zero error method. The time is displayed in large size font on a 4×20 character LCD that uses HD44780 display driver. You can synchronize the time with your computer time through a serial port.
Digital Alarm Clock Using PIC Circuit Diagram
The required power is provided through a 9 V wall adapter which is used to obtain a regulated +5 V power supply using a LM7805 IC. The microcontroller runs with a 20 MHz external clock. The backlight of LCD is driven by a PWM output from the microcontroller so that the back light intensity can be varied. The full software written in JAL is available to download. Source Code.
Source Link: www.w3circuits.com
Digital Alarm Clock Using PIC Circuit Diagram
The required power is provided through a 9 V wall adapter which is used to obtain a regulated +5 V power supply using a LM7805 IC. The microcontroller runs with a 20 MHz external clock. The backlight of LCD is driven by a PWM output from the microcontroller so that the back light intensity can be varied. The full software written in JAL is available to download. Source Code.
Source Link: www.w3circuits.com
Heat Detector Alarm Using the UM3561
A very simple heat detector alarm electronic project can be designed using the UM3561 sound generator circuit and some other common electronic parts . This heat detector electronic circuit project uses a complementary pair comprising npn and pnp transistor to detect heat . Collector of T1 transistor is connected to the base of the T2 transistor , while the collector of T2 transistor is connected to RL1 relay . T3 and T4 transistors connected in darlington configuration are used to amplify the audio signal from the UM3561 ic .
Heat Detector Alarm Circuit diagram
When the temperature close to the T1 transistor is hot , the resistance to the emitter –collector goes low and it starts conducting . In same time T2 transistor conducts , because its base is connected to the collector of T1 transistor and the RL1 relay energized and switches on the siren which produce a fire engine alarm sound . This electronic circuit project must be powered from a 6 volts DC power supply , but the UM3561 IC is powered using a 3 volt zener diode , because the alarm sound require a 3 volts dc power supply . The relay used in this project must be a 6 volt / 100 ohms relay and the speaker must have a 8 ohms load and 1 watt power .
Source Link: www.w3circuits.com
Heat Detector Alarm Circuit diagram
When the temperature close to the T1 transistor is hot , the resistance to the emitter –collector goes low and it starts conducting . In same time T2 transistor conducts , because its base is connected to the collector of T1 transistor and the RL1 relay energized and switches on the siren which produce a fire engine alarm sound . This electronic circuit project must be powered from a 6 volts DC power supply , but the UM3561 IC is powered using a 3 volt zener diode , because the alarm sound require a 3 volts dc power supply . The relay used in this project must be a 6 volt / 100 ohms relay and the speaker must have a 8 ohms load and 1 watt power .
Source Link: www.w3circuits.com
How to Create a Alarm Using 4-Buttons
To open the lock, buttons S1, S2, S3, and S4 must be pressed in this order. They must be pressed for more than 0.7 seconds and less than 1.3 seconds.
Alarm Using 4-Buttons Circuit Diagram
Reset button S5 and disable button S6 are also included with the other buttons and if the disable button is pressed, the circuit will not accept any code for 60 seconds. Each of the 3v3 zeners can be replaced with two red LEDs and this will show how you are progressing through the code. Make sure the LEDs are not visible to other users.
Source Link: www.w3circuits.com
Alarm Using 4-Buttons Circuit Diagram
Reset button S5 and disable button S6 are also included with the other buttons and if the disable button is pressed, the circuit will not accept any code for 60 seconds. Each of the 3v3 zeners can be replaced with two red LEDs and this will show how you are progressing through the code. Make sure the LEDs are not visible to other users.
Source Link: www.w3circuits.com
Simple Siren with Four Transistors
How make a Simple Siren with Four Transistors. This circuit requires only small 6V power from the speaker to generate sound two tones.
Simple Siren with Four Transistors Circuit Diagram
The circuit is more than simple. The first two transistors (left) are responsible for forming a flip-flop. This means that the 10K resistor will have a pulsed signal. The 4.7μF capacitor is charged and discharged in this signal are almost pulsating. Applied this to the oscillator (formed by the other two transistors) we obtain the desired sound output. The speaker can be any 8 ohm 1 watt the type used in portable radios
Source Link: www.w3circuits.com
Simple Siren with Four Transistors Circuit Diagram
The circuit is more than simple. The first two transistors (left) are responsible for forming a flip-flop. This means that the 10K resistor will have a pulsed signal. The 4.7μF capacitor is charged and discharged in this signal are almost pulsating. Applied this to the oscillator (formed by the other two transistors) we obtain the desired sound output. The speaker can be any 8 ohm 1 watt the type used in portable radios
Source Link: www.w3circuits.com
Low-Cost Door KnocK Alarm With Timer
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-purpose PCB and enclose in a suitable case. Fix the piezo element at the door and place the speaker in a central room inside the house using long wires. The circuit works off 5-12V DC. The music time can be adjusted through VR1 by changing the R-C time constant of the timer.
Source Link: www.w3circuits.com
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-purpose PCB and enclose in a suitable case. Fix the piezo element at the door and place the speaker in a central room inside the house using long wires. The circuit works off 5-12V DC. The music time can be adjusted through VR1 by changing the R-C time constant of the timer.
Source Link: www.w3circuits.com
Auto Turn-Off Alarm With 8-Minute Delay
Here is a very simple auto turn-off alarm with 8-minute delay circuit. 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 Diagram:
IC1 pulses counter IC2. After 8192 clocks, IC2 output (pin 3) goes high, cuts off Q2, and completes the cycle.
Source Link: www.w3circuits.com
Auto Turn-Off Alarm With 8-Minute Delay Circuit Diagram:
Source Link: www.w3circuits.com
Sensitive Optical Burglar Alarm using with 555 timer IC
This is a very simple and low-cost ELECTRONIC CIRCUIT PROJECT of sensitive optical burglar alarm circuit diagram. This sensitive optical burglar alarm uses two 555 timer ICs (IC1 and IC2). Both the ICs are wired as astable multivibrators. The first astable multivibrator built around IC1 produces low frequencies, while the second astable multivibrator built around IC2 produces audio frequencies.
Sensitive Optical Burglar Alarm Diagram:
General-purpose Darlington photo-transistor T1 is used as the light sensor. To increase the sensitivity of the circuit, NPN transistor T2 is used.
Place phototransistor T1 where light falls on it continuously. Phototransistor T1 receives light to provide base voltage to transistor T2. As a result, transistor T2 conduct to keep reset pin 4 of IC1 at low level. This disables the first multivibrator (IC1) and hence the second multivibrator (IC2) also remains reset so the alarm (LS1) does not sound.
When light falling on Darlington phototransistor T1 is obstructed, transistor T2 stops conducting and reset pin 4 of IC1 goes high. This enables the first multivibrator (IC1) and hence also the second multivibrator (IC2). As a result, a beep tone is heard from speaker LS1. The beep rate can be varied by using preset VR1, while the output frequency of IC2 can be varied by using another preset VR2.
This circuit works off a simple 6V-12V DC power supply.
PARTS LIST:
Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)
R1, R5 = 1 KΩ
R2 = 100 KΩ
R3 = 4.7 KΩ
R4 = 10 KΩ
VR1 = 1 MΩ
VR2 = 100 KΩ
Capacitors
C1 = 1 µF/16V
C2 = 0.01 µF
C3 = 0.047 µF
C4 = 0.01 µF
C5 = 47 µF/25V
Semiconductors
IC1, IC2 = NE555
Source Link: www.w3circuits.com
Doorbell Control Porch Light Using Timer IC (NE555)
This doorbell control porch light using timer ic (ne555),can be used in doorbell in order to get indication of porch light with door alarm if any one rings the door bell.
Doorbell Control Porch Light Circuit Diagram:
The circuit of doorbell control porch light is build around timer IC NE555 (IC2) and is here used as astable multivibrator. The output at pin 3 goes high of IC1 when trigger is given to pin 2 from power supply. Here transistor T1 is used as relay driver transistor which energized relay when output from pin 3 of IC1 is high. After relay energized AC current flow via N/O terminal and switch on the porch light.
Triac1 with Diac1 hear is used for switch in order to glow porch light during night and switch it off at day with the help of preset VR1 and LDR1.
Note:- Here the power source of 230V AC is replaced by 110V with replacing transformer having primary 110V and secondary 12V. Rest of the circuit of door bell controll porch light is same.
PARTS LIST:
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 1 MΩ
R2 = 10 KΩ
R3 = 470 Ω
VR1 = 100 KΩ
Capacitors
C1 = 1000 µF/25V
C2 = 22 µF/25V
Semiconductors
IC1 = NE555 (Timer IC)
T1 = BC548
DIAC1 = DB-3
TRIAC1 = BT136
D1, D2 = 1N4001
Miscellaneous
SW1 PUSH-TO-ON DPST (Double Pole Single Switch) Switch
B1 = Porch Light Bulb 100W
X1 = 230V AC primary to secondary 0-12V, 250MA secondary transformer
RL1¬ = 12V, 200 Ω 1C/O relay
Source Link: www.w3circuits.com
Doorbell Control Porch Light Circuit Diagram:
The circuit of doorbell control porch light is build around timer IC NE555 (IC2) and is here used as astable multivibrator. The output at pin 3 goes high of IC1 when trigger is given to pin 2 from power supply. Here transistor T1 is used as relay driver transistor which energized relay when output from pin 3 of IC1 is high. After relay energized AC current flow via N/O terminal and switch on the porch light.
Triac1 with Diac1 hear is used for switch in order to glow porch light during night and switch it off at day with the help of preset VR1 and LDR1.
Note:- Here the power source of 230V AC is replaced by 110V with replacing transformer having primary 110V and secondary 12V. Rest of the circuit of door bell controll porch light is same.
PARTS LIST:
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 1 MΩ
R2 = 10 KΩ
R3 = 470 Ω
VR1 = 100 KΩ
Capacitors
C1 = 1000 µF/25V
C2 = 22 µF/25V
Semiconductors
IC1 = NE555 (Timer IC)
T1 = BC548
DIAC1 = DB-3
TRIAC1 = BT136
D1, D2 = 1N4001
Miscellaneous
SW1 PUSH-TO-ON DPST (Double Pole Single Switch) Switch
B1 = Porch Light Bulb 100W
X1 = 230V AC primary to secondary 0-12V, 250MA secondary transformer
RL1¬ = 12V, 200 Ω 1C/O relay
Source Link: www.w3circuits.com
Power Supply Failure Alarm
Most of the
power supply failure indicator circuits need a separate power-supply for them-selves.
But the alarm circuit presented here needs no additional supply source. It
employs an electrolytic capacitor to store adequate charge, to feed
power to the alarm circuit which sounds an alarm for a reasonable duration when
the mains supply fails. During the presence of mains power supply, the
rectified mains voltage is stepped down to a required low level.
Power Supply Failure Alarm Circuit Diagram:
A
zener is used to limit the filtered voltage to 15-volt level. Mains presence is
indicated by an LED. The low-level DC is used for charging capacitor C3 and
reverse biasing switching transistor T1. Thus, transistor T1 remains cut-off as
long as the mains supply is present. As soon as the mains power fails, the
charge stored in the capacitor acts as a power-supply source for transistor T1.
Since, in the absence of mains supply, the base of transistor is pulled ‘low’
via resistor R8, it conducts and sounds the buzzer (alarm) to give a warning of
the power-failure.
With the value of C3 as shown, a good-quality buzzer would sound for about a minute. By increasing or decreasing the value of capacitor C3, this time can be altered to serve one’s need. Assembly is quite easy. The values of the components are not critical. If the alarm circuit is powered from any external DC power-supply source, the mains supply section up to points ‘P’ and ‘M’can be omitted from the circuit.
Following points may be noted:
With the value of C3 as shown, a good-quality buzzer would sound for about a minute. By increasing or decreasing the value of capacitor C3, this time can be altered to serve one’s need. Assembly is quite easy. The values of the components are not critical. If the alarm circuit is powered from any external DC power-supply source, the mains supply section up to points ‘P’ and ‘M’can be omitted from the circuit.
Following points may be noted:
At a higher DC voltage level,
transistor T1 (BC558) may pass some collector-to-emitter leakage current,
causing a continuous murmuring sound from the buzzer. In that case,
replace it with some low-gain transistor.
Piezo buzzer must be a continuous tone
version, with built-in oscillator. To save space, one may use five
small-sized 1000µF capacitors (in parallel) in place of bulky high-value
capacitor C3.
Source Link: www.w3circuits.com
Simple and Low-cost Gated Alarm
This Electronic Circuit Project build easy, simple and low-cost this circuit project of gated alarm. The circuit shown here employs just four components and a piezo sounder and is unlikely to be out-done for simplicity. While it does not offer the most powerful output, it is likely to be adequate for many applications.
Gated Alarm Circuit Diagram:
A dual CMOS timer IC type 7556 is used for the purpose, with each of its two halves being wired as a simple astable oscillator (a standard 556 IC will not work in this circuit, nor will two standard 555’s). Note that the CMOS7556 is supplied by many different manufacturers, each using their own type code prefix and suffix. The relevant Texas Instruments product, for instance, will be marked ‘TLC556CN’.
The circuit configuration used here is seldom seen, due probably to the inability of this oscillator to be more than lightly loaded without disturbing the timing. However, it is particularly useful for high impedance logic inputs, since it provides a simple means of obtaining a square wave with 1:1 mark-space ratio, which the ‘orthodox’ configuration does not so easily provide.
IC1.A is a slow oscillator which is enabled when reset pin 4 is taken High, and inhibited when it is taken Low. Out-put pin 5 of IC1.A pulses audio oscillator IC1.B, which is similarly enabled when reset pin 10 is taken High, and inhibited when it is taken Low.
In order to simplify oscillator IC1.B, piezo sounder X1 doubles as both timing capacitor and sounder. This is possible because a passive piezo sounder typically has a capacitance of a few tens of nanofarads, although this may vary greatly. As the capacitor-sounder charges and discharges, so a tone is emitted. The value of resistor R2 needs to be selected so as to find the resonant frequency of the piezo sounder, and with this its maximum volume.
The circuit will operate off any sup-ply voltage between 2 V and 18 V. A satisfactory output will be obtained at relatively high supply voltages, but do not exceed 18 V.
Source Link: www.w3circuits.com
Gated Alarm Circuit Diagram:
A dual CMOS timer IC type 7556 is used for the purpose, with each of its two halves being wired as a simple astable oscillator (a standard 556 IC will not work in this circuit, nor will two standard 555’s). Note that the CMOS7556 is supplied by many different manufacturers, each using their own type code prefix and suffix. The relevant Texas Instruments product, for instance, will be marked ‘TLC556CN’.
The circuit configuration used here is seldom seen, due probably to the inability of this oscillator to be more than lightly loaded without disturbing the timing. However, it is particularly useful for high impedance logic inputs, since it provides a simple means of obtaining a square wave with 1:1 mark-space ratio, which the ‘orthodox’ configuration does not so easily provide.
IC1.A is a slow oscillator which is enabled when reset pin 4 is taken High, and inhibited when it is taken Low. Out-put pin 5 of IC1.A pulses audio oscillator IC1.B, which is similarly enabled when reset pin 10 is taken High, and inhibited when it is taken Low.
In order to simplify oscillator IC1.B, piezo sounder X1 doubles as both timing capacitor and sounder. This is possible because a passive piezo sounder typically has a capacitance of a few tens of nanofarads, although this may vary greatly. As the capacitor-sounder charges and discharges, so a tone is emitted. The value of resistor R2 needs to be selected so as to find the resonant frequency of the piezo sounder, and with this its maximum volume.
The circuit will operate off any sup-ply voltage between 2 V and 18 V. A satisfactory output will be obtained at relatively high supply voltages, but do not exceed 18 V.
Source Link: www.w3circuits.com
Theft Preventer Alarm using NE 555
Here is simple alarm circuit project of Theft Preventer Alarm using NE 555 circuit. This circuit utilising a 555 timer IC can be used as an alarm system to prevent the theft of your luggage,burglars breaking into your house etc. The alarms goes ON when a thin wire, usually as thin as a hair is broken.
Theft Preventer Alarm Circuit Diagram:
The circuit is straightforward. It uses a 555 IC wired as an astable multivibrator to produce a tone of frequency of about 1kHz which gives out a shrill noise to scare away the burglar.
The wire used to set off the alarm can be made of a thin copper wire like SWG 36 or higher.
You can even use single strands of copper form a power cable.
The circuit operates on a wide range of voltages from 5V to 15V.
The speaker and the circuit could be housed inside a tin can with holes drilled on the speaker side for the sound to come out.
Source Link: www.w3circuits.com
Theft Preventer Alarm Circuit Diagram:
The circuit is straightforward. It uses a 555 IC wired as an astable multivibrator to produce a tone of frequency of about 1kHz which gives out a shrill noise to scare away the burglar.
The wire used to set off the alarm can be made of a thin copper wire like SWG 36 or higher.
You can even use single strands of copper form a power cable.
The circuit operates on a wide range of voltages from 5V to 15V.
The speaker and the circuit could be housed inside a tin can with holes drilled on the speaker side for the sound to come out.
Source Link: www.w3circuits.com
Electronic Project of Fire Alarm with LDR Sensor
This is a Electronic Alarm Circuit Project of Fire Alarm with LDR Sensor. The fire alarm circuit which use LDR to sense the smoke from the fire, so it can be used to detect any dark smoke.With the onset of summer season, possibilities of fire accidents go up. These fire accidents could be prevented if timely alarms are available. The circuit given right here alerts the user against these fire accidents. The circuit needs to be put in fire-prone locations for example a kitchen.
Fire Alarm with LDR Sensor Circuit Diagram:
Every person is aware that when everything catches fire, smoke is produced. When this smoke passes between a bulb and an LDR, the amount of light falling on the LDR reduces. This causes the resistance of LDR to raise and the voltage at pin 2 of IC 555 comes below 1/3 Vcc. thus triggering IC 555 that is utilized right here in bistable mode. As a result the voltage of pin 3 goes high. This high voltage (about 9V) completes the supply to the COB (chip-on-board).
Various COBs are available in the market to produce various sounds. Even so, one may choose a COB which produces sound for example ‘aag lag gai hai’. The signal produced by COB is amplified by an audio amplifier. In this circuit, the audio power amplifier is wired close to IC2 TDA 2002.
The sensitivity of the circuit is dependent upon the distance between bulb and LDR as well as setting of preset VR1. Thus by putting the bulb and the LDR at proper distances, one may vary preset VR1 to have optimum sensitivity.
Reset switch S1 is provided in the circuit to switch off the alarm soon after the fire has been found by the user.
Source Link:www.w3circuits.com
Fire Alarm with LDR Sensor Circuit Diagram:
Every person is aware that when everything catches fire, smoke is produced. When this smoke passes between a bulb and an LDR, the amount of light falling on the LDR reduces. This causes the resistance of LDR to raise and the voltage at pin 2 of IC 555 comes below 1/3 Vcc. thus triggering IC 555 that is utilized right here in bistable mode. As a result the voltage of pin 3 goes high. This high voltage (about 9V) completes the supply to the COB (chip-on-board).
Various COBs are available in the market to produce various sounds. Even so, one may choose a COB which produces sound for example ‘aag lag gai hai’. The signal produced by COB is amplified by an audio amplifier. In this circuit, the audio power amplifier is wired close to IC2 TDA 2002.
The sensitivity of the circuit is dependent upon the distance between bulb and LDR as well as setting of preset VR1. Thus by putting the bulb and the LDR at proper distances, one may vary preset VR1 to have optimum sensitivity.
Reset switch S1 is provided in the circuit to switch off the alarm soon after the fire has been found by the user.
Source Link:www.w3circuits.com
Piezo Alarm Using 555 Timer
This is a very simple Electronic Alarm Circuit Project of piezo alarm circuit, which will generate a sound around 110dB can be designed using this diagram. This Piezo alarm siren circuit project use two piezo sounders with high efficiency and can be powered from a wide input voltage , between 5 and 15 volts .
This circuit is very easy to build , maybe you will have a little trouble with the T1 and T2 autotransformers . Both autotransformers used in this project are the same type and require between pin 1and 2 1500 turns of 44 SWG wire and 220 turns between 2 an 3 using 40 SWgG wire.
Piezo Alarm Using 555 Timer Circuit Diagram:
In this circuit the IC1:B closest to the piezo elements is set to oscillate around their resonant frequency. The frequency is then varied via input pin 11 from the other 555, IC1:A. This modulating input is a low frequency oscillation. However, instead of using the square wave output from the first 555, the step function is converted to a triangular wave by the RC network R3 & C3 . The result of this is a frequency swept output which ensures that the output frequency definitely passes through the resonant frequency of the piezo elements sometime during each modulation cycle.
Source Link: www.w3circuits.com
This circuit is very easy to build , maybe you will have a little trouble with the T1 and T2 autotransformers . Both autotransformers used in this project are the same type and require between pin 1and 2 1500 turns of 44 SWG wire and 220 turns between 2 an 3 using 40 SWgG wire.
Piezo Alarm Using 555 Timer Circuit Diagram:
In this circuit the IC1:B closest to the piezo elements is set to oscillate around their resonant frequency. The frequency is then varied via input pin 11 from the other 555, IC1:A. This modulating input is a low frequency oscillation. However, instead of using the square wave output from the first 555, the step function is converted to a triangular wave by the RC network R3 & C3 . The result of this is a frequency swept output which ensures that the output frequency definitely passes through the resonant frequency of the piezo elements sometime during each modulation cycle.
Source Link: www.w3circuits.com
Electronic Alarm Project of Piezo with 555 Timer
This is a very simple Electronic Circuit Project of piezo alarm circuit. Piezo alarm which will generate a sound around 110dB can be designed using this diagram. This Piezo alarm siren circuit diagram use some common components like 555 timer ic, you can use two 555 timer circuits or one 556 circuit.
Electronic Alarm Project of Piezo with 555 Timer Circuit Diagram:
This Piezo alarm siren circuit project use two piezo sounders with high efficiency and can be powered from a wide input voltage, between 5 and 15 volts. This circuit is very easy to build, maybe you will have a little trouble with the T1 and T2 auto-transformers. Both auto-transformers used in this project are the same type and require between pin 1and 2 1500 turns of 44 SWG wire and 220 turns between 2 an 3 using 40 SWG wire.
In this circuit the IC1:B closest to the piezo elements is set to oscillate around their resonant frequency. The frequency is then varied via input pin 11 from the other 555, IC1:A. This modulating input is a low frequency oscillation. However, instead of using the square wave output from the first 555, the step function is converted to a triangular wave by the RC network R3 & C3. The result of this is a frequency swept output which ensures that the output frequency definitely passes through the resonant frequency of the piezo elements sometime during each modulation cycle.
Source Link: www.w3circuits.com
Fire Alarm With Thermistor
Small and simple unit, Can be used for Home-Security purpose. In this fire alarm circuit, a Thermistor works as the heat sensor. When temperature increases, its resistance decreases, and vice versa. At normal temperature, the resistance of the Thermistor (TH1) is approximately 10 kilo-ohms, which reduces to a few ohms as the temperature increases beyond 100 C. The circuit uses readily available components and can be easily constructed on any general-purpose PCB.
Fire Alarm Using Thermistor Circuit diagram:
Circuit Operation:
Timer IC NE555 (IC1) is wired as an astable multivibrator oscillating in audio frequency band. Switching transistors Q1 and Q2 drive multivibrator IC1. The output of IC1 is connected to NPN transistor Q3, which drives the loudspeaker (SPKR) to generate sound. The frequency of IC1 depends on the values of resistors R6, R7 and capacitor C2. When Thermistor TH1 becomes hot, it provides a low-resistance path to extend positive voltage to the base of transistor Q1 via diode D2 and resistor R3. Capacitor C1 charges up to the positive voltage and increases the ‘on’ time of alarm.
The higher the value of capacitor C1, the higher the forward voltage applied to the base of transistor Q1. Since the collector of transistor Q1 is connected to the base of transistor Q2, transistor Q2 provides positive voltage to reset pin 4 of IC1. R5 is used such that IC1 remains inactive in the absence of positive voltage. D2 stops discharging of capacitor C1 when the Thermistor connected to the positive supply cools down and provides a high-resistance (10k) path.
It also stops the conduction of Q1. To prevent the Thermistor from melting, wrap it up in mica tape. The circuit works off a 6V-12V regulated power supply. D1 is used to indicate that power to the circuit is switched on.Link
Parts:
R1 470R
R2 470R
R3 33K
R4 560R
R5 470R
R6 47K
R7 2.2K
R8 470R
C1 10uF-16V
C2 0.04uF-63V
C3 0.01uF-63V
Q1 BC548
Q2 BC558
Q3 SL100B
D1 Red Led
D2 1N4001
IC1 NE555
SPKR 1W-8R
TH1 Thermistor-10K
Source Link: www.w3circuits.com
Fire Alarm Using Thermistor Circuit diagram:
Circuit Operation:
Timer IC NE555 (IC1) is wired as an astable multivibrator oscillating in audio frequency band. Switching transistors Q1 and Q2 drive multivibrator IC1. The output of IC1 is connected to NPN transistor Q3, which drives the loudspeaker (SPKR) to generate sound. The frequency of IC1 depends on the values of resistors R6, R7 and capacitor C2. When Thermistor TH1 becomes hot, it provides a low-resistance path to extend positive voltage to the base of transistor Q1 via diode D2 and resistor R3. Capacitor C1 charges up to the positive voltage and increases the ‘on’ time of alarm.
The higher the value of capacitor C1, the higher the forward voltage applied to the base of transistor Q1. Since the collector of transistor Q1 is connected to the base of transistor Q2, transistor Q2 provides positive voltage to reset pin 4 of IC1. R5 is used such that IC1 remains inactive in the absence of positive voltage. D2 stops discharging of capacitor C1 when the Thermistor connected to the positive supply cools down and provides a high-resistance (10k) path.
It also stops the conduction of Q1. To prevent the Thermistor from melting, wrap it up in mica tape. The circuit works off a 6V-12V regulated power supply. D1 is used to indicate that power to the circuit is switched on.Link
Parts:
R1 470R
R2 470R
R3 33K
R4 560R
R5 470R
R6 47K
R7 2.2K
R8 470R
C1 10uF-16V
C2 0.04uF-63V
C3 0.01uF-63V
Q1 BC548
Q2 BC558
Q3 SL100B
D1 Red Led
D2 1N4001
IC1 NE555
SPKR 1W-8R
TH1 Thermistor-10K
Source Link: www.w3circuits.com
Car Alarm Sound Booster
Here is a Simple Electronic circuit Project For car alarms, emphasis should be put on hearing the audible alert and identifying it as belonging to your ‘wheels’.Unfortunately, modern car alarm systems seem to have more or less the same alarm sound especially if they are from the same brand. Also, to comply with legal noise restrictions, the alarm sound is not always loud enough to be heard if the car is parked down the road.
The circuit shown here is designed to help boost the alarm sound by also activating the car’s horn(s) when the alarm goes off.Internally the car alarm system often provides a signal that activates the (optional) engine immobilizer and/or volume (ultrasound) sensors. This signal usually goes Low upon system triggering and high again when the alarm system is deactivated.
Car Alarm Sound Booster Circuit Diagram :
The alarm activation signal is fed to the circuit through D1. When in idle state, T1’s gate is High and consequently the FET conducts, keeping power FET T2 firmly switched of f. When the system gets an active low signal, T1 switches of f allowing timing capacitor C2 to charge via R2. About 15 seconds later, when the voltage across C2 is high enough, T2 starts to conduct and relay RE1 is energized. This, in turn, provides the required path for the ‘lights flashing’ signal to energize RE2 and feed battery power to the car’s horn(s).
When the alarm system is turned off the activation signal returns to High. T1 starts to con-duct and rapidly discharges C2 via R3. T2 is then cut off and RE1 is de-energized. Diode D2 suppresses back EMF from RE1.The circuit draws less than 2 mA when idling. When activated the circuit’s current consumption is virtually that of the RE1 coil.RE1 is any simple SPST or SPDT relay, capable of switching about 0.5 A (at 12 V). The coil rating is for 12 VDC and a current requirement as low as you can find. Fuse F1 should be a slow blow type and rated about twice RE1’s coil current.
The BS170 in position T2 can sink a continuous current of about 0.5 A. However, a value of 1.2 A pulsed is specified by Fairchild for their devices. To keep the FET’s d-s current due to C2 discharging within safe limits, R2 may be increased, C2 decreased and R3 increased, all proportionally.
A factor of 2 will keep the FET out of harm’s way with maybe a slight change in the 15-second delay and the sensitivity of the circuit.C1 is used as a smoothing capacitor and F2 should be rated in accordance with the horn(s) maximum current draw.
Caution.The installation and use of this circuit may be subject to legal restrictions in your country, state or area.
Source Link: www.w3circuits.com
The circuit shown here is designed to help boost the alarm sound by also activating the car’s horn(s) when the alarm goes off.Internally the car alarm system often provides a signal that activates the (optional) engine immobilizer and/or volume (ultrasound) sensors. This signal usually goes Low upon system triggering and high again when the alarm system is deactivated.
Car Alarm Sound Booster Circuit Diagram :
The alarm activation signal is fed to the circuit through D1. When in idle state, T1’s gate is High and consequently the FET conducts, keeping power FET T2 firmly switched of f. When the system gets an active low signal, T1 switches of f allowing timing capacitor C2 to charge via R2. About 15 seconds later, when the voltage across C2 is high enough, T2 starts to conduct and relay RE1 is energized. This, in turn, provides the required path for the ‘lights flashing’ signal to energize RE2 and feed battery power to the car’s horn(s).
When the alarm system is turned off the activation signal returns to High. T1 starts to con-duct and rapidly discharges C2 via R3. T2 is then cut off and RE1 is de-energized. Diode D2 suppresses back EMF from RE1.The circuit draws less than 2 mA when idling. When activated the circuit’s current consumption is virtually that of the RE1 coil.RE1 is any simple SPST or SPDT relay, capable of switching about 0.5 A (at 12 V). The coil rating is for 12 VDC and a current requirement as low as you can find. Fuse F1 should be a slow blow type and rated about twice RE1’s coil current.
The BS170 in position T2 can sink a continuous current of about 0.5 A. However, a value of 1.2 A pulsed is specified by Fairchild for their devices. To keep the FET’s d-s current due to C2 discharging within safe limits, R2 may be increased, C2 decreased and R3 increased, all proportionally.
A factor of 2 will keep the FET out of harm’s way with maybe a slight change in the 15-second delay and the sensitivity of the circuit.C1 is used as a smoothing capacitor and F2 should be rated in accordance with the horn(s) maximum current draw.
Caution.The installation and use of this circuit may be subject to legal restrictions in your country, state or area.
Source Link: www.w3circuits.com
Low-cost Flashing Signal Alarm with LEDs
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 generated.
Source link: www.w3circuits.com
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 generated.
Source link: www.w3circuits.com
