Powering my Arduino with a 9V external supply, which allows the onboard regulators to function, the Arduino's 5V output was sufficiently clean.
Based on the supplies used in testing, ripple of more than about 10 mV is problematic. A truly clean supply will show 0.000 VAC. You can check how clean a power supply is by checking it with an oscilloscope or volt meter, set to the AC Volts (or, if provided, the AC millivolts) range. One exhibited as much as 30 mV ripple on the supply output, an as a result, the the Sound Detector was rather sensitive and unstable. In testing with various supplies, a significant degree of variability was discovered - some supplies are less noisy than others. Therefore, the Sound Detector may require more careful power supply configuration than many circuits. The next circuit in the chain is a high-gain amplifier, so any noise on the supply will then be amplified. Since the capsule is effectively a voltage divider sitting across the power rails, it will transcribe any noise on the supply lines onto the capsule output. The Sound Detector is an analog circuit, and as such, it's more sensitive to noise on the power supply than most digital circuits. Both of these factors need to be accounted for when deploying the Sound Detector. Also, the JFET is rather sensitive to noise on the power supply. Since capacitors are sensitive to loading, it's internally buffered with a JFET ( junction field-effect transistor).ĭue to the mechanical and electronic tolerances involved, some capsules are more sensitive than others. The diaphragm moves in response to sound, and the capacitance changes as the plates get closer together or farther apart, causing the divider to change. That capacitor forms a voltage divider with the external bias resistor. Inside the capsule is the diaphragm, which is actually one plate of a small capacitor. These capsules have a couple of quirks that we need to understand in order to apply them successfully. The heart of the Sound Detector is the electret microphone capsule - without it, we couldn't convert acoustic energy into electrical energy. Configuration Care and Feeding Of The Capsule
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