FIRE SIREN USES FLASHER

A low-drain circuit powered by a 1.5-V cell utilizes the National LM3909 flasher IC to simulate a fire-alarm siren. Pressing a button generates a rapidly increasing wail, with the tone decreasing in frequency once the button is released. The sound produced by the loudspeaker mimics that of a motor-driven siren, and the volume is sufficient for a child's pedal car.

The circuit design employs the LM3909 integrated circuit, which is specifically designed for low-power applications. The IC operates by generating a series of pulses that can be used to drive a loudspeaker. In this configuration, the output frequency of the LM3909 is modulated by the pressing of a button, which initiates the sound production.

When the button is pressed, the circuit enters an active state, causing the output to produce a rapidly rising tone. This is achieved through a combination of timing resistors and capacitors that dictate the frequency and duration of the pulse signal generated by the LM3909. As the button is released, the frequency gradually decreases, simulating the natural decay of a siren sound.

The loudspeaker is connected to the output of the LM3909, which amplifies the generated audio signal. The choice of a low-drain design allows for extended battery life, making it suitable for portable applications such as toys or alarm systems. The circuit can be further enhanced with additional components such as a volume control potentiometer or a filter to adjust the sound quality, depending on specific requirements.

Overall, this circuit represents an effective application of the LM3909 flasher IC in creating audible alerts in a compact and energy-efficient manner, making it ideal for use in child-friendly environments.Low-drain circuit operating from 1. 5-V cell uses National LM3909 flasher IC to simulate fire-alarm siren. Pressing button produces rapidly rising wail, with tone coasting down in frequency after button is released. Sound from loudspeaker resembles that of motor-driven siren. Volume is adequate for child`s pedal car. -P. Lefferts, Power-Miser Flashe r IC Has Many Novel Applications, EDN Magazine, March 20, 1976, p 59-66. 🔗 External reference