Correctly adjusting the Soundlazer

Now that people have starting playing with their Soundlazers, I wanted to take a minute to explain how to properly adjust the oscillator and PWM modulator.

First, you will obviously need access to the Soundlazer board and also an Oscilloscope.

Switch in middle position, no audio cable attached, power on.

  1. Attach the oscilloscope ground (-) to the GND test point on the Soundlazer board
  2. Attach the signal lead of the oscilloscope to the PWM test point on the Soundlazer Board
  3. Adjust the PWM trimpot (R20) so that the PWM shifts at 180 degrees as shown in the photo (equal positive and negative square waves)
  4. Adjust the Freq (R21) trimpot for 39.4 -39.6 kHz output signal.  This frequency was chosen to have the best output with least distortion.  Feel free to experiment with other frequencies and you may want to offset the PWM slightly to see what happens.*
* Some people have noticed a low volume tone produced by the ultrasonic array.  This is a result of the ultrasonic transducers “ringing” when they are in perfect tune.  The resulting tone is simply a subharmonic frequency of the 40KHz signal (20kHz, 10kHz, 5kHz, 2.5kHz, etc).  To eliminate this tone, simply adjust the Freq (R21) trimpot to a slightly higher or lower frequency.  The tone will disappear but the transducers may not oscillate at the optimal frequency.   You will need to experiment with this adjustment to find the best spot for your application.


The current Sigma Studio program has three settings on the switch:

Left) Audio Beam Off

Middle) Normal Audio Output (leave here for most cases)

Right) Test Tone

For those of you who have purchased a Sigma Studio Developers Kit, feel free to change the software to make the switch do different things.  One Soundlazer firmware upgrade that I haven’t had the time to make would be an audio signal detector that shuts all ultrasonic audio off if no voice/music is present.  This is a great way to conserver power and your ears!

If you look at the schematic, you will see that the switch and the ultrasonic oscilator are wired directly into the DSP which gives you the ability to customize the Soundlazer in many ways.

As usual, have fun experimenting and let me know what you come up with.