Fire Alarm Circuit using IC 555

This fire alarm circuit created based on thermistor and a timer circuit 555. The IC1 (NE555 Timer IC) is configured as an oscillator operating at an audio frequency. The transistors T1 and T2 IC1 unit. The output (pin 3) of IC1 is at the basis of the transistor pairs T3 (SL100), which drives the speaker to generate the alarm sound. NE555 frequency depends on the values ​​of resistors R5 and R6 and C2 capability.

When thermistor is heated, it gives a low resistance path to the positive voltage to the base of transistor T1 through diode D1 and resistor R2. Capacitor C1 charges to the positive supply voltage and increases the time for which the alarm is activated. The higher the value of C1, the higher the positive bias applied to the base of the transistor T1 (BC548). As the collector of T1 is coupled to the base of transistor T2, the transistor T2 provides a positive voltage to pin 4 (reset) of IC1 (NE555).

Resistance R4 is selected remains inactive NE555 s0 that in the absence of positive voltage. Diode D1 stops discharging the capacitor C1 when the thermistor is related to the positive supply voltage is cooled out and provides a path of high resistance. It also inhibits the bias of the transistor T1.

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IC 555 based on water Activated Alarm

This water activated alarm circuit uses a NE555 timer wired as an astable oscillator and powered by the emitter current of transistor BC109C. In dry conditions, the transistor having no bias current and be completely off. As the probe gets wet, a small current flowing between the base and the emitter and the transistor turns on. A higher current flow in the collector circuit allows the IC NE555 osillator sound.

Probe / contacts may use a nonreactive metal. Contacts gold plated or silver age relay can be used, however, a cheaper alternative is the thread of alternate strips of copper a piece of veroboard. These will eventually oxidize over but as very little current flowing in the base circuit, the higher the impedance caused by oxidation is not important. No base resistor is necessary as the transistor is in emitter follower, current limit is the impedance at the emitter (the oscillator circuit)

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Refrigerator Door Alarm Circuit Using LDR

Refrigerator Door Alarm Circuit Using LDR

The alarm circuit closed in a small box in the refrigerator is placed near the lamp. With the camera inside the fridge is in the dark, the LDR R2 has a high resistance to both clamping IC1 by holding 12-pin high. When a ray of light enters through the opening, or fridge lamp lights, the LDR resistance decreases, the pin 12 goes low, IC1 starts counting and, after a preset delay (20 seconds in this case) piezoelectric alarm beeps for 20 seconds. then stops during the same period of time and the cycle repeats until you close the refrigerator door. D2 connected to pin 6 of IC1 allows the piezo sounder beeping 3 times per second.

Note:

• Delay time can be varied changing C1 and/or R3 values.
• Quiescent current drawing is negligible, so SW1 can be omitted.
• Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.
• Do not put this device in the freezer.

List Component:

R1    : 10K
r2    : LDR any type
R3,R4 : 100K
C1    : 10nF
C2    : 100µF/25V
D1,D2 : 1N4148
IC1   : 4060 14 stage ripple counter and oscillator IC
Q1    : BC337
BZ1   : Piezo sounder (incorporating 3KHz oscillator)
SW1   : SPST slide Switch
B1    : 3V Battery

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Phone Alarm Dialer using MT8880 and PIC 16F84A

Phone Alarm Dialer using MT8880 and PIC 16F84A

Just angle this Anxiety Buzz Dialer up to article you would like to monitor, for example, a aerial baptize alarm, low temperature alarm, aback window, barn door, etc. Back the arrangement is activated it will anxiety a cardinal of programmed numbers to let you apperceive the anxiety has been activated. This would be abundant to get alerts of anxiety altitude from your home back you are at work.

The ambit uses a MT8880 DTMF dialer dent and a PIC 16F84A microcontroller. After putting calm this little device, you charge access programming-mode to apprentice some buzz numbers which this bore will anxiety afterwards audition an ascribe on it’s sensor pin.

After programming aloof accumulation ability to the device. Afterwards acute the button “Pokreni dojavu alarma” it will alpha to punch (tone or pulse, depending on the jumper setup). Back the buzz anxiety is auspiciously established, the alleged affair should columnist batter key “#” to stop the accessory from calling addition cardinal or again.

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