It’s most likely that you’ll find the detector to be too sensitive. In testing the board for this writeup, noisy air
conditioning and music in the next office were enough to set it off. To make the board less sensitive, you can lower
the preamplifier gain by populating R17 in parallel with R3.
R3 Value
R17 Value
Arithmetic Gain
Gain (dB)
100K
-
100
40
100K
100K
50
33
100K
47K
32
30
100K
22K
18
25
100K
10K
9
19
100K
4.7K
4
13
100K
2.2K
2
6
Raising The Gain
If you want to make the sound detector more sensitive, so that it will be activated by quieter sounds, you can
remove R3, and populate R17.
R17 Value
Arithmetic Gain
Gain (dB)
100K
100
40
220K
220
46
470K
470
53
1Meg
1000
60
Lights Out
In some applications, the onboard LED may be distracting or undesirable. To disable it, simply use a solder sucker
or wick to remove the solder blob from the jumper near the LED.
Physical Considerations
The electret capsule on the Sound Detector is also sensitive to mechanical vibration and wind noise.
The Sound Detector will pick up handling noise. Mounting it with a resilient material can help absorb vibration –
placing it on a piece of open-cell foam helped reject vibration conducted through the testing workbench. Other
resilient mounting strategies would include suspending it using rubber bands, or building shock absorbers using #4
machine screws and heat-shrink tubing.
Wind noise is caused when blasts of air enter the capsule. Examples would be a windy day, or the sharp
exhalation that often accompanies syllables such “p,” “b” and “t.” The capsule come with a thin fabric covering, but
it may not be enough to prevent stronger blasts. You can craft a more robust windscreen with open-cell foam or
