Distributed Network Data

Chapter 4. Finishing the Breadboard

Now that our sensor platform both measures the current environmental conditions and looks out for motion, let’s add our final sensor and finish building our prototype.

The Sensor

The next sensor we’ll add is one to detect changes in ambient noise levels.

Electret Microphone

We’re going to use the electret microphone breakout board from Adafruit Industries (see Figure 4-1). The board comes with a capsule microphone and supporting hardware including, an op-amp and a potentiometer to allow you to adjust the gain.

Electret microphones are small, omnidirectional microphones commonly used in cell phones and laptops. They can have an extremely wide frequency response; the one we’re using has a 20Hz to 20kHz frequency response. They are small, very cheap to produce, and quite sensitive. Unfortunately, they also have some drawbacks, including a very uneven frequency response, high noise floor, and high levels of distortion. Despite that, they’re a good choice if fidelity isn’t an overriding issue for your application.

Since the electret microphone only produces a few milli-volts peak-to-peak, it needs to be coupled with an op-amp before it can be used. The Adafruit breakout board uses a Maxim MAX4466 for this purpose.

Figure 4-1. The Adafruit Electret Microphone Amplifier back with potentiometer (left) and front with the transducer (right)

Wiring the Breadboard ...