Project 16 (Moderate): Ultrasonic Alarm System (Version 1)

This is my favorite project yet. I've created a motion detector that scans the room and if it detects any object within 25cm, the speaker will go nuts.

As for the alarm, a piezo buzzer is not very loud. so I went to a local electronics store and bought new speakers + an audio amplifier. An audio amplifier pretty much converts small inputs and outputs something much bigger. The arduino digital pin can only output 5 volts and any more would damage the board. In order to make the speaker louder, I need more voltage. That's where the audio amplifier comes in.












At first, the arduino board was suppling all the power but I noticed that the LCD display was flickering.
Due to the high power requirements, I need an external power source. A 9 volt battery will be powering the audio amplifier, which means the speaker will be even louder than before. 4 AA batteries(about 5 volts) will power the servo motor. The arduino will only be powering the LCD display and the ultrasonic sensor. With this setup, the LCD display is no longer flickering!

Features:
- an ultrasonic sensor, mounted onto a servo motor will scan for nearby objects(can detect objects up to 3 meters away!)
- the distance will be displayed on a LCD display
- once the alarm is triggered, "INTRUDER ALERT!!" will be displayed on the LCD

Parts:
- 1x ultrasonic sensor
- 1x servo motor
- 1x RGB LCD display (16 X 2)
- 1x 8 ohm speaker (0.25 watt)
- 1x 10k potentiometer
- 1x lm386
- 1x 220uf capacitor
- 1x 9v battery and a battery holder (to power the audio amplifier)



Scanner Limits

The ultrasonic sensor has a range from 2cm to 3 meters. Also, I noticed that the sensor has issues detecting corners. This is because the sound waves emitted from the sensor will bounce off the surface at an angle. Instead of going directly back to the sensor, it will then bounce off another surface, and then back. Thus it will take a lot longer for the sensor to read the sound. The longer it takes to read the sounds, the farther the distance is. Also, any object that can absorb sound(ex. sponges) will disrupt the readings.