Friday, September 19, 2014
Fire alarm circuit
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.
Notes.
- 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 schema 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.
Thursday, September 18, 2014
Simple Fire Alarm
Here is a simple circuit which can be used as a Fire Alarm. 3 Volt is enough to operate. There is not much to the circuit. The IC UM66 is connected to its supply and its output fed to a transistor for amplification.
Circuit diagram :
Simple Fire Alarm Circuit Diagram
UM66 is a complete miniature tone generator with a ROM of 64 notes, oscillator and a preamplifier. For amplification we have used a NPN transistor which is BC548. Here BC548 makes a common emitter circuit. For limiting the base current we have used a resistance of 220 Ohms so that transistor will not get damaged even if IC is wrong connected.
For heat sensor we have used tube light starter in place of manual switch. In a starter there is a metal plate and a pin with small gap. When starter gets heated then metal plate of starter expands and get in contact with the pin and circuit is completed and we get audio from speaker. For fast sensing we can use starter without its glass body by carefully breaking glass cover.
Friday, August 22, 2014
Heat Sensor Fire Detector Pyroelectric
These sensors form of Lithium Tantalate pyroelectric parallel opposed dual element high gain detector with integrated analog signal processing. These sensors can detect heat changes from -40 to +70 degrees Celsius without change siginfikan of noise and sensitivity.