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Description:
Smoke detectors are generally used in advanced alarm systems. Most of this professional devices use gas-detectors, ionization rooms or radioactive elements as sensors. In this circuit we are not using any of this complicated components. Instead of these, we are using two LDRs and one LED.
LM1801 special-purpose IC ,which is designed especially for smoke detectors, provides us building this circuit by using the minimum number of components. It includes one internal zener supply, two reference voltage outputs, one voltage comparator, fixing diodes and one 500mA output transistor.
Circuit is connected to the mains directly. D1 rectifies the alternating source and R7 reduces it to the level that the circuit can operate with. C2 capacitor stabilizes the voltage and zener inside the IC regulates it
Two identical LDRs are connected in bridge type so this connection prevents the circuit from temperature changes and ageing effects...
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Description:
Ultrasonic Burglar Alarm: Transmitter
and receiver parts of the circuit are connected each other by using a
triple cable. System operates with 20V supply and 10V effective output
voltage drives the ultrasonic transducer at its highest value.
Transmitter circuit gives the maximum gain at 40kHz.
Ultrasonic
transducers in the circuit must be placed vis-à-vis and when a barrier
passes between them it must block the connection without affected from
reflections.
Transmitter is continuously operating and generating
40kHz ultrasonic oscillations. Receiver is designed to operate only when
no ultrasonic signal reaches it and it produces an output signal. You
can connect an alarm system with a relay to the output of the receiver.
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Description:
Ultrasonic
oscillations which are generated by unmodulated ultrasonic transmitters
commonly for remote control are usually affected from other ultrasonic
sources in the media and that's why we are giving a 500Hz modulated
ultrasonic transmitter circuit here.
Voltage supply of the
circuit is 9 Volts and any change of the value will change the
frequency also. You can omit this difference by connecting a resistor
between A and B nodes. You can find the value of the resistor by using
this formula:
R = (Vsupply - 7V) / O.6 Kohm where Vsupply is the new supply voltage value.
The
multivibrator generates 500Hz modulation frequency. To avoid the
frequency differences , tolerance of the circuit should not exceed %5.
If the circuit components changed, then the frequency can be determined by using the formula below,
f = (1.44 x 1000) / (C2 x R3 x C3 x R2)
If C1 and C3 are nanofarads then R2 and R3 will be magaohms.
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