Skema Rangkaian|Electronic Schematic Circuit Diagram » Alarm

NE555 Electronic Buzzer Schematic

Mon, 25 Jan 2010 01:34:55 +0000

NE555 Electronic Buzzer Schematic

This accessible cyberbanking buzzer ambit congenital based on timer works for accepting the frequency. The IC timer NE 555 acclimated as astable multivibrator operating at about 1kHz and produces a complete back switched on. The complete abundance can be adapted by capricious the 10K resistor. You may change the 10K resistor with capricious resistor.

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Fire Alarm Circuit Using LDR

Mon, 07 Sep 2009 21:20:55 +0000

Fire Alarm Circuit Using LDR

Here is a simple fire alarm circuit based on a LDR and lamp pair for sensing the fire.The alarm works by sensing the smoke produced during fire.The circuit produces an audible alarm when the fire breaks out with smoke.

When there is no smoke the light from the bulb will be directly falling on the LDR.The LDR resistance will be low and so the voltage across it (below .6V).The transistor will be OFF and nothing happens.When there is sufficient smoke to mask the light from falling on LDR, the LDR resistance increases and so do the voltage across it.Now the transistor will switch to ON.This gives power to the IC1 and it outputs 5V.This powers the tone generator IC UM66 (IC2) to play a music.This music will be amplified by IC3 (TDA 2002) to drive the speaker.

The diode D1 and D2 in combination drops 1.4 V to give the rated voltage (3.5V ) to UM66 .UM 66 cannot withstand more than 4V.
* The speaker can be a 8Ω tweeter.
* POT R4 can be used to adjust the sensitivity of the alarm.
* POT R3 can be used for varying the volume of the alarm.
* Any general purpose NPN transistor(like BC548,BC148,2N222) can be used for Q1.
* The circuit can be powered from a 9V battery or a 9V DC power supply.
* Instead of bulb you can use a bright LED with a 1K resistor series to it.

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Skema Rangkaian Alaram Kebakaran

Mon, 07 Sep 2009 21:18:36 +0000

Many fire alarm circuits are presented here,but this time a new circuit using a thermistor and a timer to do the trick. The circuit is as simple and straight forward so that , it can be easily implemented.The thermistor offers a low resistance at high temperature and high resistance at low temperature. This phenomenon is employed here for sensing the fire.

The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output(pin 3) of IC1 is couples to base of transistor T3(SL100), which drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2.When thermistor becomes hot, it gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2. Capacitor C1 charges up to the positive supply voltage and increases the the time for which the alarm is ON. The larger the value of C1, the larger the positive bias applied to the base of 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). Resistor R4 is selected s0 that NE555 keeps inactive in the absence of the positive voltage. Diode D1 stops discharging of capacitor C1 when the thermistor is in connection with the positive supply voltage cools out and provides a high resistance path. It also inhibits the forward biasing of transistor T1.

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