How To Make An LRAD With Arduino

The LRAD sound is part of a crowd control system also known as the Long Range Acoustic Device. It is used by law enforcement and government agencies worldwide as an alternative to lethal force. In the previous articles, we discussed exactly how the LRAD system works and even took one apart to see what was inside.

In this article, we will begin looking at ways in which we can create our own non-lethal sound canon and explore the possibilities for uses. These types of devices are perfect for home security, vagrancy issues, and anywhere this very disturbing sound can move people away from harm.

Analysis in our previous article of the audio output from the Long Range Acoustic Device shows that the sound frequencies are within the mid-ranges of normal hearing levels between 2200Hz and 3200Hz. We also see that the sweep is a positive direction in a few millisecond bursts.

Parts Needed For LRAD Sound Generator

Recreating this sound should be easy with some off the shelf Arduino parts. We will need the following components:

  1. Arduino Uno or any other Arduino compatible board.
  2. Audio Amplifier (Adafruit #2130 or similar)
  3. 8 Ohm speaker or horn (MOTOROLA KSN1001A will work best)
  4. USB Cable
  5. Jumper Wires.


If you don’t want to wait for the Adafruit 2130 shield, any audio amplifier will work. If you do use a home stereo or similar, be very careful to protect your ears because the sound created by this design is very loud and could cause ear damage at close proximity. You can connect the ground and pin five through a 10uf capacitor to the audio input of any audio amplifier.

Actual recorded LRAD sound (adjust the volume to the minimum before playing)

The easiest way to reproduce the LRAD warning tone is to generate it using the Arduino tone library. A few simple lines should do the trick. Plug your Arduino into your computer’s USB and upload this simple code.

As soon as you compile and upload this code to your Arduino, a square wave on pin#5 should start pulsing. Using square waves via the PWM signal on Arduino is a common way to reproduce simple sounds. There is nothing very complex about the LRAD sound since it is basically generating a single tone at any moment in time. The signal is just changing frequencies at a relatively slow rate so we should be able to reproduce the sound without any complex coding.

void setup ()
{
}

void loop(){
 int x = 7; /* loop step count */
 int i;

/* LRAD frequence warning tone frequency is 2.2kHz to 3.2kHz*/

/* Postive Sweep */ 
   for (i = 2200; i <= 3200; i=i+x) {
   tone(5, i); 
   delay(1);} 

}

I played around with the timing and think this is the best reproduction of the LRAD sound using a simple Arduino microcontroller. It is very likely that the actual LRAD units produce these sounds in the exact same way although the code and timing may be slightly different.


About the Arduino Code

First, Setup the Arduino

void setup ()
{
}

Set integers and step count for loop (This controls the sweep time)

void loop(){
int x = 7; /* loop step count */
int i;

Start the tone value at 2200 Hz and count up to 3200 Hz in steps of 7 Hz

for (i = 2200; i <= 3200; i=i+x) {
tone(5, i); (generates tone on pin 5 based on the current value of “i”

I chose an odd value of 7 for the step because that number seemed to fit the actual timing of the original sound as close as possible.

A very small delay before starting over

delay(1);}

End Arduino code.


If you are using the Adafruit 2130 with an Arduino Uno, you can install the header pins on the bottom side and line the rightmost pins up with VIN and GND. You will still need to jumper the second ground to the negative terminal of the audio input labeled “A-” along with Arduino Pin #5 to “A+”

Do not worry about the A0 and A1 pins getting shorted. These are set as input pins and will have no real electrical connection unless you accidentally write some extra code to switch them to outputs by mistake. Wiring the board this way is easiest and completely safe.

The wiring for the LRAD sound generator

In this article, we are only focusing on the warning tone itself. There is much more technology inside an LRAD than just the tone generator. The magnetic coils, horns, and audio amplifiers are all specifically designed to project high-pressure soundwaves in one direction. In order to recreate the entire system, we will need to explore the many unique properties found within this Long Range Acoustic device.

Unless we want to transmit voice along with the warning tones, the Motorola KSN1001A horn tweeters are a great choice. Although they are not really designed for mid-range frequencies like the ones we are generating, they do offer directionality along with high power capability.

We could assemble around a dozen of these horn tweeters into a circular frame and use any high power home or car audio amplifier to drive them. With this type of setup, we could get well over 110dB of sound pressure output and maybe even match the loudness of the original LRAD. If we were planning to transmit voice, we will need lower frequency response speaker arrays and more complex horn designs.

Uses For Our LRAD Sound Generator

While we are limited to only sending a high power warning tone with our design, there still are many uses for this type of device.

  • Alarm systems
  • Crowd Control
  • Vagrancy deterrent
  • Bird chaser
  • Dog bark trainer

Now keep in mind that while these types of devices are very directional in nature, they still produce a significant amount of noise off to the sides. This is true with all actual LRAD models and our DIY LRAD sound generator. LRADs do not use ultrasonic audio as the misinformation on the internet claims, they are nothing more than well designed directional bullhorns with standard audio drivers as components.