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DIY Ambulance Siren

The urgent wail of an ambulance siren is an unmistakable sound, signaling a nearby emergency. Whether you have a professional need for a siren, or simply want to construct one, you can assemble your own ambulance or police siren. This procedure will imitate the sound at an adjustable high and low frequency, and can be mounted on a vehicle or stationary object depending on your preference. It's also ideal for kids who want to enhance one of their toys. Note that "uF" stands for "microfarad."

Things You'll Need

.01 or .02 uF disc capacitor
47 uF electrolytic capacitor
2 47K resistors
1 1.5K resistor
1 PNP power transistor
1 NPN transistor
1 PC board
Soldering gun
Speaker
9 volt battery
Pushbutton switch

Instructions

- 1
  Place the PC board on a flat surface and prepare the soldering gun. Install the 47 uF capacitor, making sure to line up the polarity markings.
- 2
  Install one of the 47 K resistors next to the capacitor. Then install the disc capacitor.
- 3
  Install the other 47K capacitor along with the PNP power transistor. The metal side of the power transistor must be face-up for the siren to work. Then solder the NPN transistor. Make sure all the solderings are intact before proceeding.
- 4
  Connect the speaker to two points on the PC board. Connect the pushbutton to the other two points. A doorbell works well as a pushbutton, but any two wires will suffice. Make sure one pushbutton wire is connected to the negative point and the other to the positive point. Press the power button; the device should produce an ambulance-like wail.
- 5
  Mount the siren in a box or enclosure for an extra touch. Old coffee or juice cans serve well as enclosures.

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