Police Siren
Abstract
The purpose of this project was to design and create an operational police siren that uses two timers and an 8 ohm speaker. A potentiometer would then be added to adjust the pitch of the siren. Utilizing the design program DipTrace, I was able to design a circuit 3x3 inch circuit board with two LM555 timers and a potentiometer to adjust the oscillation frequency of the second timer. After installing all components using lead-free solder and using a 12V power source supplied by an IME 156 project, the project became operational and the potentiometer was able to change the pitch.
Project Description
The main components in creating the Police Siren are two LM155 timers, a potentiometer, and an 8 Ohm Piezo buzzer. One timer is used to control the frequency (time between high and low points of the siren wave) and the other is used to control the tone (actual sound given off by buzzer). The potentiometer is then used to adjust the second timer to alter the pitch of the buzzer.When the push button is depressed (enters a closed position), the circuit will be powered ON and Timer U1 will start to oscillate at a frequency of .8 Hz through the connection of 10k and 82k Ohm resistor as well as a 10uF Electrolytic Capacitor.This output frequency from pin 3 (output pin) of Timer U1 is fed into pin 5 (control pin) of Timer U2 where the frequency becomes adjusted by a 10K Ohm resistor. The tone generated can be varied by changing the values of potentiometer VR1 (turning the potentiometer CCW lowers the tone and turning it CW increases the tone). The output of Timer U2 is used to drive a power transistor Q1 which in turn powers the 8 ohm buzzer. Diode D2 is used to prevent the damage of transistor Q1 from an EMF generated by the speaker during the ON/OFF driving of the speaker.
Conclusion
I was able to successfully create a police Siren that used a 12V power source supplied by an IME156-created Power Source. By turning the potentiometer, the tone output by the 8Ohm buzzer was successfully changed. In making the board, I had 3 surface mount pieces that I had to add to the board. Because of their size (and recommendation from Dr. Pan) I was able to use standard lead-solder and soldering iron rather than having to use solder paste and a reflow oven.
Downloads
- Schematic (JPEG)
- Project Report (PDF)