siren alarm circuit diagram usng lm358

Posted on Feb 4, 2014

When the switch is pressed C3 charges up through R4 with a time constant of 0. 47 seconds and when the switch is released C3 begins a slower discharge through R7 and R3 with a time constant of about 5 seconds. The op amp 358 used in this project is set up as a voltage controlled oscillator. When the output of the oscillator (pin 7) switches low the

siren alarm circuit diagram usng lm358
Click here to download the full size of the above Circuit.

re is a charge remaining in C1 which holds pin 5 below the switching point. Current through R7 is proportional to the control voltage on C3. This current discharges C1 causing the voltage on pin 5 to rise towards the switching point at a rate proportional to the voltage on C3. When the switching point is reached pin 7 switches high and initially pulls pin 6 high via C1. This causes the op amp to temporarily turn on hard. But C3 quickly recharges through D2 causing the voltage on pin 5 to fall below the switching point and causing the op amp to switch off again. The positive pulse output from the op amp puts a fixed amount of charge into C2 slightly raising the potential of pin 6. This causes the potential on pin 6 to rise and assist the sharp switch off of the op amp. Also R5 & C2 delay the rise on pin 6 long enough to get a good output pulse.

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    4 Watt audio Amplifier
    Digital oscillator
    Relay Output Proximity Sensor
    Long distance infrared transmitter circuit diagram
    in circuit transistor checker
    Protection Circuit For Electrical Appliances From Power Supply Variations PCB
    Power Amplifier OCL 100w With MJ802 MJ4502
    DIY Infrared Remote Extender Unit
    Precision frequency counter
    AP500 and its application circuit ab